ASTM E1998-11(2018)

Standard Guide for Assessing Depressurization-Induced Backdrafting and Spillage from Vented Combustion Appliances

SIGNIFICANCE AND USE
5.1 Although a number of different methods have been used to assess backdrafting and spillage (see NFPA 54, CAN/CGSB-51.71, and 1-4)6 a single well-accepted method is not yet available. At this point, different methods can yield different results. In addition, advantages and drawbacks of different methods have not been evaluated or described.  
5.2 To provide a consistent basis for selection of methods, this guide summarizes different methods available to assess backdrafting and spillage. Advantages and limitations of each method are addressed.  
5.3 One or more of the methods described in this guide should be performed when backdrafting or spillage from vented combustion appliances is suspected to be the cause of a potential problem such as elevated carbon monoxide (CO) levels or excessive moisture.  
5.4 The following are examples of specific conditions under which such methods could be performed:  
5.4.1 When debris or soot is evident at the draft hood, indicating that backdrafting may have occurred in the past,  
5.4.2 When a new or replacement combustion appliance is added to a residence,  
5.4.3 When a new or replacement exhaust device or system, such as a downdraft range exhaust fan, a fireplace, or a fan-powered radon mitigation system, is added,  
5.4.4 When a residence is being remodeled or otherwise altered to increase energy efficiency, as with various types of weatherization programs, and  
5.4.5 When a CO alarm device has alarmed and a combustion appliance is one of the suspected causes of the alarm.  
5.5 Depending on the nature of the test(s) conducted and the test results, certain preventive or remedial actions may need to be taken. The following are examples:  
5.5.1 If any of the short-term tests indicates a potential for backdrafting, and particularly if more than one test indicates such potential, then the appliance and venting system should be further tested by a qualified technician, or remedial actions could be taken in accordance w...
SCOPE
1.1 This guide describes and compares different methods for assessing the potential for, or existence of, depressurization-induced backdrafting and spillage from vented residential combustion appliances.  
1.2 Assessment of depressurization-induced backdrafting and spillage is conducted under either induced depressurization or natural conditions.  
1.3 Residential vented combustion appliances addressed in this guide include hot water heaters and furnace. The guide also is applicable to boilers.  
1.4 The methods given in this guide are applicable to Category I (draft-hood- and induced-fan-equipped) furnaces. The guide does not apply to Category III (power-vent-equipped) or Category IV (direct-vent) furnaces.  
1.5 The methods in this guide are not intended to identify backdrafting or spillage due to vent blockage or heat-exchanger leakage.  
1.6 This guide is not intended to provide a basis for determining compliance with code requirements on appliance and venting installation, but does include a visual assessment of the installation. This assessment may indicate the need for a thorough inspection by a qualified technician.  
1.7 Users of the methods in this guide should be familiar with combustion appliance operation and with making house-tightness measurements using a blower door. Some methods described in this guide require familiarity with differential-pressure measurements and use of computer-based data-logging equipment.  
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.9 This guide does not purport to address all safety concerns, if any, associated with its use. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and to determine the applicability of regulatory limitations prior to use. Carbon monoxide (CO) exposure or flame roll-out may occur when performing certain proc...

General Information

• Status: Published
• Publication Date: 30-Jun-2018
• ICS: 91.140.65 - Water heating equipment
• Technical Committee: E06 - Performance of Buildings
• Drafting Committee: E06.41 - Air Leakage and Ventilation Performance

Relations

• Replaces: ASTM E1998-11 - Standard Guide for Assessing Depressurization-Induced Backdrafting and Spillage from Vented Combustion Appliances
• Effective Date: 01-Jul-2018
• Refers: ASTM D1356-20a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Sep-2020
• Refers: ASTM D1356-20 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Mar-2020
• Refers: ASTM E779-19 - Standard Test Method for Determining Air Leakage Rate by Fan Pressurization
• Effective Date: 01-Jan-2019
• Refers: ASTM E779-10(2018) - Standard Test Method for Determining Air Leakage Rate by Fan Pressurization
• Effective Date: 15-Jul-2018
• Refers: ASTM D1356-15a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Oct-2015
• Refers: ASTM D1356-15 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Jul-2015
• Refers: ASTM E631-15 - Standard Terminology of Building Constructions
• Effective Date: 01-Mar-2015
• Refers: ASTM D1356-14b - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Dec-2014
• Refers: ASTM E631-14 - Standard Terminology of Building Constructions
• Effective Date: 01-Nov-2014
• Refers: ASTM D1356-14a - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-May-2014
• Refers: ASTM D1356-14 - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 15-Jan-2014
• Refers: ASTM D1356-05(2010) - Standard Terminology Relating to Sampling and Analysis of Atmospheres
• Effective Date: 01-Apr-2010
• Refers: ASTM E779-10 - Standard Test Method for Determining Air Leakage Rate by Fan Pressurization
• Effective Date: 15-Jan-2010
• Refers: ASTM E631-06 - Standard Terminology of Building Constructions
• Effective Date: 01-Jun-2006

Overview

ASTM E1998-11(2018): Standard Guide for Assessing Depressurization-Induced Backdrafting and Spillage from Vented Combustion Appliances provides guidance on selecting and applying methods used to evaluate the potential for, or actual occurrence of, backdrafting and spillage in residential combustion appliances. Backdrafting and spillage can lead to dangerous indoor air quality issues such as elevated carbon monoxide (CO) and moisture levels. This ASTM guide compares various assessment approaches, details their advantages and limitations, and encourages consistent application to improve safety and indoor air quality.

Key Topics

• Backdrafting and Spillage Risks: The guide highlights conditions where depressurization within a residence can cause combustion products to enter living spaces, rather than venting outdoors as intended.
• Assessment Methods: Various techniques are summarized, including both quick, short-term tests under induced depressurization and longer-term monitoring under natural conditions.
• Applicability: The guide specifically addresses Category I combustion appliances, such as draft-hood-equipped furnaces, boilers, and water heaters, and does not apply to power-vented or direct-vent models.
• Visual and Instrumental Checks: Recommendations are provided for initial visual inspections (e.g., soot or debris at draft hoods) and the use of diagnostic instruments for pressure and combustion gas measurement.
• When to Test: Scenarios such as evidence of soot, the installation of new appliances, addition of exhaust devices, or home weatherization activities are identified as key triggers for assessment.
• Safety Precautions: The guide stresses the importance of technician safety, including CO monitoring during testing and referral to qualified professionals when findings indicate hazards or appliance malfunctions.

Applications

Practical uses of ASTM E1998-11(2018) include:

• Indoor Air Quality Investigations: When CO alarms are triggered, or if moisture or soot is discovered, this guide helps determine if backdrafting and spillage may be the cause.
• Pre-Purchase or Home Inspection: Assessing vented combustion appliances before purchasing a property or after renovations ensures safe indoor air quality.
• Post-Modification Testing: Any time new combustion appliances, fireplaces, or exhaust fans are installed, or after energy efficiency improvements are made, these methods help verify proper venting under normal and induced conditions.
• Preventive Maintenance: Contractors and technicians can use the guide to check for potential problems during routine service calls or before weatherization to ensure appliances operate safely under varying pressure conditions in the home.
• Remediation Planning: The guide supports decisions on corrective measures, such as increasing makeup air, improving venting systems, or replacing problematic appliances if tests indicate unacceptable backdrafting or spillage.

Related Standards

ASTM E1998-11(2018) references and complements several key industry standards and codes related to vented combustion appliances and indoor air quality:

• NFPA 54: National Fuel Gas Code - Establishes safety requirements for fuel gas piping and appliances.
• CAN/CGSB-51.71: The Spillage Test - Canadian standard for evaluating pressure-induced spillage risk.
• ANSI Z21.47 - Gas-fired central furnace safety requirements.
• ASTM E779: Test Method for Determining Air Leakage Rate by Fan Pressurization - Relevant for those conducting blower door tests as part of house depressurization assessments.

These documents, together with ASTM E1998, provide a comprehensive foundation for ensuring the safety and performance of vented residential combustion equipment through standardized assessment and consistent, repeatable field methods.

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Keywords: ASTM E1998, depressurization, backdrafting, spillage, vented combustion appliances, carbon monoxide, indoor air quality, residential safety, standard guide, appliance inspection, NFPA 54, CAN/CGSB-51.71, HVAC testing, blower door, energy efficiency, remedial actions.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1998 − 11 (Reapproved 2018)
Standard Guide for
Assessing Depressurization-Induced Backdrafting and
Spillage from Vented Combustion Appliances
This standard is issued under the fixed designation E1998; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.9 This guide does not purport to address all safety
concerns, if any, associated with its use. It is the responsibility
1.1 Thisguidedescribesandcomparesdifferentmethodsfor
of the user to establish appropriate safety, health, and envi-
assessing the potential for, or existence of, depressurization-
ronmental practices and to determine the applicability of
induced backdrafting and spillage from vented residential
regulatory limitations prior to use. Carbon monoxide (CO)
combustion appliances.
exposure or flame roll-out may occur when performing certain
1.2 Assessment of depressurization-induced backdrafting
procedures given in this guide. See Section 7, for precautions
andspillageisconductedundereitherinduceddepressurization
that must be taken in conducting such procedures.
or natural conditions.
1.10 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.3 Residential vented combustion appliances addressed in
thisguideincludehotwaterheatersandfurnace.Theguidealso ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
is applicable to boilers.
mendations issued by the World Trade Organization Technical
1.4 The methods given in this guide are applicable to
Barriers to Trade (TBT) Committee.
Category I (draft-hood- and induced-fan-equipped) furnaces.
The guide does not apply to Category III (power-vent-
2. Referenced Documents
equipped) or Category IV (direct-vent) furnaces.
2.1 ASTM Standards:
1.5 The methods in this guide are not intended to identify
D1356 Terminology Relating to Sampling and Analysis of
backdrafting or spillage due to vent blockage or heat-
Atmospheres
exchanger leakage.
E631 Terminology of Building Constructions
1.6 This guide is not intended to provide a basis for E779 TestMethodforDeterminingAirLeakageRatebyFan
Pressurization
determining compliance with code requirements on appliance
and venting installation, but does include a visual assessment 2.2 CAN/CGSB Standard:
CAN/CGSB51.71 TheSpillageTest—MethodtoDetermine
of the installation. This assessment may indicate the need for a
thorough inspection by a qualified technician. the Potential for Pressure-Induced Spillage from Vented,
Fuel-Fired;SpaceHeatingAppliances;WaterHeaters,and
1.7 Users of the methods in this guide should be familiar
Fireplaces
with combustion appliance operation and with making house-
2.3 ANSI Standard:
tightness measurements using a blower door. Some methods
ANSI Z21.47 Gas-fired Central Furnace
described in this guide require familiarity with differential-
2.4 NFPA Standard:
pressure measurements and use of computer-based data-
NFPA 54 National Fuel Gas Code
logging equipment.
1.8 The values stated in SI units are to be regarded as
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
standard. No other units of measurement are included in this
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
standard.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Available from Canadian General Standards Board (CGSB), 11 Laurier St.,
This guide is under the jurisdiction of ASTM Committee E06 on Performance Phase III, Place du Portage, Gatineau, Quebec K1A0S5, Canada, http://www.tpsgc-
of Buildings and is the direct responsibility of Subcommittee E06.41 on Air pwgsc.gc.ca/ongc-cgsb.
Leakage and Ventilation Performance. Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
Current edition approved July 1, 2018. Published July 2018. Originally approved 4th Floor, New York, NY 10036, http://www.ansi.org.
in 1999. Last previous edition approved in 2011 as E1998 – 11. DOI: 10.1520/ Available from National Fire Protection Association (NFPA), 1 Batterymarch
E1998-11R18. Park, Quincy, MA 02169-7471, http://www.nfpa.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1998 − 11 (2018)
3. Terminology system fans, and vented combustion appliances (boilers,
fireplaces, furnaces, or water heaters). Thus, the existence and
3.1 Definitions:
extent of house depressurization at a specific location varies
3.1.1 For definitions of general terms related to building
over time, depending on outdoor conditions and the operation
construction used in this specification, refer to Terminology
of indoor appliances.
E631,andforgeneraltermsrelatedtosamplingandanalysisof
3.2.12 induced conditions, n—conditions for house depres-
atmospheres, refer to Terminology D1356.
surization created with the use of exhaust fans or blower door.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 air leakage, n—the movement or flow of air through
3.2.13 induced draft (ID) fan, n—a fan used in a venting
the building envelope which is driven by a pressure differential
system that removes flue gases under non-positive static vent
across the envelope.
pressure.
3.2.13.1 Discussion—An appliance with an ID fan is a
3.2.2 air leakage rate, n—the volume of air movement per
Category I appliance, as its venting system is under non-
unit time across the building envelope.
positive static vent pressure.
3.2.3 airtightness, n—the degree to which the building
3.2.14 intermittent pressure differential, n—the incremental
envelope resists flow of air.
house depressurization due to fans that are operated
3.2.4 blower door, n—a fan pressurization device incorpo-
intermittently, such as clothes dryer, kitchen exhaust or bath-
rating a controllable fan and instruments for airflow measure-
room fan.
ment and building pressure difference measurement that
3.2.15 natural conditions, n—outdoortemperatureandwind
mounts securely in a door or other opening.
conditions that create house depressurization.
3.2.5 Category 1 appliance, n—an appliance that operates
3.2.16 pressure differential, n—pressure difference across
with non-positive static pressure and with a vent gas tempera-
the building envelope, expressed in pascals (inches of water or
ture that avoids excessive condensate production in the vent
pound-force per square foot or inches of mercury).
(see NFPA 54).
3.2.17 vented combustion appliance, n—includes fossil-
3.2.6 Category III appliance, n—an appliance that operates
fuel-fired furnace, boiler or water heater vented to outside.
with a positive vent pressure and with a vent gas temperature
3.2.17.1 Discussion—The term vented combustion appli-
that avoids excessive condensate production in the vent (see
ances in this standard excludes fireplaces and gas logs vented
NFPA 54).
to outside. Also, it does not include appliances such as gas
3.2.7 Category IV appliance, n—an appliance that operates
ranges or unvented space heaters.
with a positive vent pressure and with a vent gas temperature
that may cause excessive condensate production in the vent
4. Summary of Guide
(see NFPA 54).
4.1 This guide summarizes different methods for assessing
3.2.8 combustion system spillage, n—entry of combustion
backdrafting and spillage from vented combustion appliances.
products into a building from dilution air inlets, vent connector
For each method the equipment needed, test procedures, data
joints, induced draft fan case opening, combustion air inlets, or
reporting, results and interpretation, and technician and test
otherlocationsinthecombustionorventingsystemofavented
time required are presented. Advantages and uncertainties of
combustion appliance (boiler, fireplace, furnace, or water
each method are discussed.
heater), caused by backdrafting, vent blockage, or leaks in the
4.2 Assessment of depressurization-induced backdrafting
venting system.
andspillageisconductedundereitherinduceddepressurization
3.2.9 continuous pressure differential, n—the incremental
or natural conditions. Depressurization is induced in a resi-
house depressurization due to fans that can be operated
dence by deliberately operating exhaust fans or a blower-door
continuously, such as furnace blower or supply/exhaust venti-
fan. Assessments conducted under induced conditions can
lator.
indicate only the potential for backdrafting and spillage.
3.2.10 downdrafting, n—the reversal of the ordinary (up-
Assessments under natural conditions can indicate actual
ward)directionofairflowinachimneyorfluewhennovented backdrafting and spillage events. Assessments under either
combustion appliances are operating (as opposed to
induced or natural conditions may not be valid for weather,
backdrafting, which occurs when vented combustion appli- house tightness, or operational conditions beyond those en-
ances are operating).
countered during the period of measurements.
3.2.11 house depressurization, n—the situation, pertaining 4.3 The guide includes four types of short term tests
to a specific location in a house, whereby the static pressure at
conducted under induced conditions: (1) house depressuriza-
that location is lower than the static pressure in the immediate
tion test with preset criteria; (2) downdrafting test; (3) appli-
vicinity outside the house.
ancebackdraftingtest;and(4)coldventestablishmentpressure
3.2.11.1 Discussion—The pressure difference between in- (CVEP) test.Acontinuous backdraft test to identify backdraft-
doors and outdoors is affected by building tightness (including ingeventsundernaturalconditions,whichinvolvescontinuous
the distribution of leakage sites across the building envelope), monitoring of vent differential pressures, is also described. For
indoor-outdoor temperature difference, local winds, and the identification of spillage events or consequences thereof under
operation of indoor appliances such as exhaust fans, forced-air natural conditions, a continuous spillage test that involves
E1998 − 11 (2018)
continuous monitoring of spillage-zone temperatures and in- 5.5.3 Possible remedial actions include the following:
doorairqualityisdescribed.Becausetheyareconductedunder
5.5.3.1 Ataminimum,aCOalarmdevicecouldbeinstalled
a variety of naturally occurring conditions, the continuous
in the house.
methods can provide more definitive results for conditions
5.5.3.2 Limiting the use of devices or systems that increase
under which tests are conducted. However, the continuous
house depressurization, such as fireplaces and high-volume
methods also can be more time-consuming and resource-
exhaust fans. Proper sealing of any air leakage sites, especially
intensive to apply.
at the top floor ceiling level, can also reduce house depressur-
ization at the lower levels of the house.
4.4 A purpose of the guide is to encourage the use of
consistent procedures for any selected method.
5.5.3.3 Partially opening a window in the furnace or appli-
ance room, if available. Keeping the door nearest the appliance
5. Significance and Use
room open at all times or putting louvers in the door.
5.1 Although a number of different methods have been used 5.5.3.4 Providing increased makeup air for the appliance
toassessbackdraftingandspillage(seeNFPA54,CAN/CGSB- (for example, by providing a small duct or opening to the
51.71, and 1-4) a single well-accepted method is not yet outdoors near the appliance).
available. At this point, different methods can yield different
5.5.4 If remedial actions are not successful, then consider-
results. In addition, advantages and drawbacks of different
ationcanbegiventocorrectingorreplacingtheventingsystem
methods have not been evaluated or described.
or, if necessary, replacing the spilling appliance with one that
can better tolerate house depressurization.
5.2 To provide a consistent basis for selection of methods,
this guide summarizes different methods available to assess
5.6 The understanding related to backdrafting and spillage
backdrafting and spillage. Advantages and limitations of each
phenomena is evolving. Comprehensive research using a
method are addressed.
single, reliable method is needed to better understand the
5.3 One or more of the methods described in this guide frequency, duration, and severity of depressurization-induced
should be performed when backdrafting or spillage from spillage in a broad cross section of homes (5). In the absence
vented combustion appliances is suspected to be the cause of a of a single well-accepted method for assessing the potential for
potential problem such as elevated carbon monoxide (CO) or occurrence of backdrafting or spillage, alternative methods
levels or excessive moisture. are presented in this guide. The guide is intended to foster
consistent application of these methods in future field work or
5.4 The following are examples of specific conditions under
research. The resultant data will enable informed decisions on
which such methods could be performed:
relative strengths and weaknesses of the different methods and
5.4.1 When debris or soot is evident at the draft hood,
provides a basis for any refinements that may be appropriate.
indicating that backdrafting may have occurred in the past,
Continuedeffortsalongtheselineswillenablethedevelopment
5.4.2 When a new or replacement combustion appliance is
of specifications for a single method that is acceptable to all
added to a residence,
concerned.
5.4.3 When a new or replacement exhaust device or system,
such as a downdraft range exhaust fan, a fireplace, or a
6. Principles and Methods
fan-powered radon mitigation system, is added,
5.4.4 When a residence is being remodeled or otherwise
6.1 Background—Residences can be depressurized due to
altered to increase energy efficiency, as with various types of
operationofexhaustequipmentandimbalancedairdistribution
weatherization programs, and
systems, as well as local weather. The extent of house
5.4.5 When a CO alarm device has alarmed and a combus-
depressurization depends on the capacity of the exhaust
tion appliance is one of the suspected causes of the alarm.
equipment, the degree of imbalance in the air distribution
system, and the airtightness of the building envelope. Outdoor
5.5 Dependingonthenatureofthetest(s)conductedandthe
temperatures also can affect the depressurization of the house.
test results, certain preventive or remedial actions may need to
For example, the natural depressurization of a house would be
be taken. The following are examples:
a few to several pascals greater under winter conditions in the
5.5.1 If any of the short-term tests indicates a potential for
northern parts of the country than during summer.The changes
backdrafting, and particularly if more than one test indicates
in depressurization of the house due to outdoor conditions
suchpotential,thentheapplianceandventingsystemshouldbe
(temperature and wind) often can be greater than changes
further tested by a qualified technician, or remedial actions
caused by exhaust appliances. Downdrafting, which can result
could be taken in accordance with 5.5.3.
from house depressurization, is the reversal of the ordinary
5.5.2 If continuous monitoring indicates that backdrafting is
(upward) direction of air flow in a chimney or flue when no
occurring, and particularly if it indicates that spillage is
vented combustion appliances are operating. Backdrafting
occurringthatimpactsindoorairquality(forexample,elevated
generally occurs when an appliance starts up against a down-
CO concentrations or excessive moisture in the house), then
drafting chimney and cannot establish draft. Vented combus-
remedial action is indicated.
tion appliances equipped with draft hoods or diverters or
induced-draft fans depend on hot flue gases to create a thermal
buoyancy that exhausts combustion products through a chim-
The boldface numbers in parentheses refer to a list of references at the end of
this standard. ney. When the natural or induced draft or thermal buoyancy
E1998 − 11 (2018)
cannot overcome backdrafting, there will be spillage of com- assessedbymeasuringairqualityintheareawherecombustion
bustion products including carbon dioxide (CO ), carbon appliances are located.
monoxide (CO), nitrogen oxides (NO ) and water vapor into
x
6.4 Methods—The available methods for assessing back-
indoor spaces.
drafting and spillage can be divided into two major groups:
6.2 Principles of Vent Operation and Backdrafting—Asche- those conducted under induced depressurization and those
matic of one typical installation of a water heater and furnace conducted under natural conditions. Methods used under in-
connected to a common B-vent (chimney) through vent con- duced conditions can provide an indication of the potential for
nectors is shown in Fig. 1.There can be a number of variations backdrafting. The tests conducted under induced conditions
to this example, including vent connectors that are connected require less testing time than those under natural conditions
to a masonry chimney, or separate venting systems for each and, thus, are termed short-term tests. Ideally, short-term tests
appliance. Draft-hood or induced-draft combustion appliances should be repeated under different weather conditions. Meth-
depend on the thermal buoyancy of hot flue gases related near ods used under natural conditions detect actual backdrafting
the chimney. In the case of backdrafting, or reversal of the and spillage events but require continuous monitoring over a
ordinary vent flow, hot flue gases tend to follow the path with period typically one week or longer. The period of continuous
the smallest pressure or least resistance. For draft-hood- monitoring, ideally, should be long enough to cover a range of
equipped appliances, the path of least resistance is the draft weather conditions. Relationships between the results of short-
hood or diverter. For induced-draft furnaces, this path could be term tests under induced conditions and continuous monitoring
either at the draft hood of the other appliance (for example, undernaturalconditionshavebeeninvestigated (6, 7, 8)butare
water heater) that is connected to the common vent, or around not yet qualified or established.
leakage points in the vent system, especially at connections.
6.5 The methods included in this guide are grouped under
6.3 Principles of Assessment—Since the upward flow in the two categories: induced conditions and natural conditions.
chimney or venting system depends on pressure differentials 6.5.1 Induced Conditions include house depressurization
created by the buoyancy of hot flue gases, measurement of the testwithpresetcriteria,downdraftingtest,appliancebackdraft-
static pressure in the vent system (relative to that in the room ing test, and cold vent establishment pressure (CVEP) test.
where the appliance is located) is one basic measurement 6.5.1.1 The following general rules apply in conducting
parameter to indicate backdrafting. Spillage of the flue gases tests under induced conditions: (1) when such tests are
around the draft hood or diverter can be observed visually or initiated, the temperature of the common vent should be close
inferred from a temperature sensor. (The visual test, which to the temperature of the mechanical room, so that the test
provides a reliable indication of backdrafting, can be accom- approximates a cold vent condition; and (2) testing of a water
plished by using a smoke pencil or a small flame created by a heater should precede furnace or boiler testing, as the water
cigarettelightertoindicatetheflowdirectionofthefluegases.) heater has a lower heat output and will require a correspond-
Quantitative assessment of the impact of spillage at the draft ingly shorter time to cool the common vent following its
hood or diverter cannot be accomplished without special operation.
equipment, because of the temperature and moisture content of 6.5.2 Natural Conditions include continuous backdrafting
flue gases. However, the consequences of spillage can be
test, and Continuous spillage test.
6.6 Observations and tests for assessing hazards, given in
Section7,shouldbefollowedpriortoconductingthetests.The
tests for assessing backdrafting and spillage are summarized,
beginning in Section 8, in terms of equipment needed, the
condition of the house for testing, test procedures, technician
time needed, test duration, and test outputs and their interpre-
tation.
7. Hazards and Assessment
7.1 Amajor hazard in conducting the tests described in this
guide is CO exposure. Flame roll-out and associated fire
potential is another potential hazard (9). Hazards associated
with blower-door testing must also be considered. Hazards
associated with blower-door testing are noted in Test Method
E779; precautions and tests for other hazards are given below.
7.2 Carbon Monoxide Exposure—In some situations, appli-
ances may generate CO due to backdrafting. It is imperative
that flue CO levels be measured prior to conducting any tests
and that continuous CO monitoring be conducted in the
mechanical room or the appliance area (test space) while these
tests are occurring. The procedures for flue CO measurements
FIG. 1 Schematic of Combined Water Heater and Furnace Venting
System are given below.
E1998 − 11 (2018)
7.2.1 Flue CO Measurements Prior to Conducting Tests— 7.2.2.2 As an additional margin of safety, technicians are to
For flue CO measurements, use a combustion analyzer that is observe the CO levels in the mechanical room during these
capable of measuring flue CO levels on an air-free basis. All tests and note any time when the ambient concentration
exhaust devices in the house, including fireplaces or wood- exceeds 100 ppm for 15 min. Testing is to be terminated in
burning stoves, should be off during the testing period. such instances. It is unlikely that the ambient concentration
will exceed 100 ppm when the flue-gas concentration is below
7.2.1.1 Place the sampling probe for the combustion ana-
400 ppm.
lyzer under the water heater draft hood and down into the
7.2.2.3 Should the CO alarm activate, any test in progress
throat of the heat exchanger as far as possible. Ensure that the
should be terminated and the house temporarily evacuated and
probe’s thermocouple (if present) is not in contact with metal.
ventilated.
RecordflueCOlevelsatleastonceperminwhentheappliance
is fired.
7.3 Visual Assessment:
7.2.1.2 Turndownthefurnacethermostat.Turnonthewater 7.3.1 Verifythatthereisnofuelorotherflammablematerial
stored in the mechanical room or area and that no combustible
heater by turning its thermostat to the highest setting. Open a
hotwaterfaucettoensurethatthewaterheatercontinuestofire materialisstoredwithin2ftoftheappliances(furnaceorwater
heater) to be tested.
during the test.
7.3.2 Make a visual assessment for scorch marks on the
7.2.1.3 Wait until 5 min have elapsed since the appliance
outside of the water heater near the burner to see if flame-
was started. Using a match or a smoke pencil, check for draft
rollout may have happened previously. If there is evidence of
atthewaterheaterdrafthood(lackofdraftindicateslikelihood
scorching (such as at the base of the water heater), then further
of a blocked vent).
testing should be postponed until a qualified technician has
7.2.1.4 Remove the sampling probe, shut off the faucet and
tested the appliance.
return the water heater thermostat to its original setting.
7.3.3 During forced backdrafting conditions flame roll-out
7.2.1.5 If the furnace has an induced draft (ID) fan, drill a
may occur, even if there is no evidence of prior occurrences,
sampling hole just above the furnace collar and insert the
becauserelativelyhighdepressurizationconditionsareinduced
sampling probe through this hole. Otherwise, place the sam-
with a blower door under this method. Should flame roll-out
pling probe under the furnace draft hood and into the heat
occur, the test should be discontinued.
exchanger if possible. Record flue CO levels at least once per
7.3.4 A qualified technician should visually inspect the
min when the appliance is fired.
venting system to determine that there is no blockage or
7.2.1.6 Turn on the furnace and set the thermostat suffi-
restriction, leakage, corrosion, or other deficiencies that could
ciently high that it will continue to fire for at least 5 min.
cause an unsafe condition, check for proper size and horizontal
7.2.1.7 Wait until 5 min have elapsed, and conduct a match
pitch, and ensure compliance with local codes.
or smoke pencil test as in 7.2.1.3.
8. House Depressurization Test With Preset Criteria (see
7.2.1.8 Remove the sampling probe and return the thermo-
NFPA 54, CAN/CGSB-51.71, and Refs. 1-4)
stat to its original setting. If a sampling hole was drilled, insert
8.1 Summary of Procedure—Details of this procedure are
a plug or screw to close it.
given in CAN/CGSB-51.71. In summary, the test is conducted
7.2.1.9 If the CO value for the water heater or furnace flue
under closed-house conditions (exterior doors, windows, fire-
gases exceeds 400 ppm (air-free basis as described in ANSI-
placeorwoodstovedampers,orboth,closed).Interiordoorson
Z21.47), or there is evidence of a blocked vent, then further
perimeterroomsthatdonotcontainexhaustdevicesareclosed.
testing should be postponed until a qualified technician has
The water and furnace remain off throughout the test. Follow-
visited the house to resolve any such apparent problems.
ing baseline measurements of the indoor-outdoor pressure
7.2.2 CO Monitoring During the Tests—Several levels of
difference with all continuous and intermittent house fans off,
protection against excessive CO exposure due to induced
the incremental house depressurization due to continuous fans
backdrafting of combustion appliances, based on existing
(furnace blower, combined supply and exhaust ventilator,
standards or guidelines for CO concentrations in flue gases and
continuousairexhaustorsupplysystems)andintermittentfans
in ambient air, should be considered. Occupational Safety and
(clothes dryer, kitchen exhaust, bathroom fans, fireplace simu-
Health Administration (OSHA) guidelines for CO exposure
lator) is measured. The continuous pressure differential and
limit concentrations to 200 ppm for short-term (15 min)
intermittent pressure differential are then compared with preset
exposure and 50 ppm for 8-hour-average exposure. The sensor
criteria to determine pass or fail status.
for CO monitoring in the test space should have a visual
8.2 Equipment Needed—A differential pressure measuring
readout that will alert technicians to unusual concentrations in
device, outdoor pressure tube, outdoor pressure averaging
the breathing zone of their activity. Additionally, a CO alarm
system, and a wood-fire simulator, are needed.
device is to be installed in the living area of the house during
8.3 House Conditions—Set the house conditions according
these tests.
to Table 1.
7.2.2.1 If the CO level in the flue gas exceeds 400 ppm
(air-free basis as described in ANSI-Z21.47) during the visual 8.4 Procedures:
inspection or during backdrafting or CVEP tests, then the 8.4.1 Set Up Differential Pressure Measurement—Connect
affected test is to be terminated. The responsible appliance indoor and outdoor ports to a differential-pressure measure-
shouldbeinspectedortestedortunedbyaqualifiedtechnician. mentdevice.Theportforindoorsshouldbein,orconnectedby
E1998 − 11 (2018)
TABLE 1 Initial House Conditions for House Depressurization
8.4.7 Record Continuous Pressure Differential—Record the
A
Test
maximum pressure differential created by continuous ventila-
House Feature Configuration
tion systems; this differential, after subtracting the baseline
Windows Close
depressurization value obtained in 8.4.2, is termed the continu-
Exterior doors Close
ous pressure differential.
Basement door Close
Doors on an enclosed furnace room Close
8.4.8 Turn on Exhaust Fans—This includes clothes dryer, if
Interior doors on perimeter rooms not Close
itexhauststotheoutdoors;kitchenexhaust,ifitexhauststothe
containing exhaust devices
outdoors or in attics; and other intermittent exhaust fans rated
Chimney with manual damper Close
Chimney without manual damper Leave as is
at more than 75 L/s (159 CFM).
Make-up air supply with manual damper Close
8.4.9 Simulate a Fire in an Open Fireplace—Open chimney
Make-up air supply without damper Leave as is
damper. Open air combustion air supply to the fireplace. Place
Woodstove or fireplace No fire: close doors and air
control dampers
a wood-fire simulator (camping stove, typically 9.5 J/h or
Fuel-fired appliances (furnace, boiler, Turn down thermostats
10 000 Btu/h) in the fireplace. Temporarily open a nearby door
water heater, gas fireplace, pellet stove)
Floor drains Fill with water or window to the outdoors. Light the simulator and adjust to a
Exhaust and supply fans Off
highrateofburn.Allowatleast5minforthechimneytowarm
Ventilating and air moving devices Off
up. Tightly close the door or window to the outdoors.
Clothes dryer Off
Attic hatch Close
8.4.10 Record Intermittent Pressure Differential—Read and
Crawl space vents Close
record the maximum pressure differential due to exhaust fans
Broken windows and other short term openings Tape over
and fire simulators, in combination with continuous ventilation
Sub-slab ventilation fans or subfloor ventilation Turn off
systems for soil gas control
systems: this differential, after subtracting the baseline value
A
See NFPA 54. obtained in 8.4.2, is termed the intermittent pressure differen-
tial.
8.5 Data Reporting:
8.5.1 Record measured depressurization levels in pascals
tubing to, the room containing the appliance(s) to be tested.
(Pa) caused by any forced-air circulating fans and combined
The port for outdoors should be connected by tubing to one or
supply and exhaust ventilators.
more outdoor sites. It is preferable to have outdoor sites on
8.5.2 Record continuous and intermittent pressure differen-
each side of the house that are connected to the outdoor port
tials.
through a common manifold. To minimize the effect of local
windsontheoutdoorpressuremeasurement,andtoavoidsnow
8.6 Results and Interpretations:
or rain accumulation, or both, each outdoor hose should be
8.6.1 House depressurization limits specified in CAN/
placed in an open-ended housing that faces downward. The
CGSB-51.71 are 5 Pa continuous and intermittent for open
housing should be attached to a vertical stake or stand near a
combustion appliances (buoyancy systems with draft hoods or
cornerformedbytheexteriorwallandtheground(astagnation
relief-air openings, and 5 Pa continuous and 10 Pa intermittent
region), near the midpoint of the wall.
for closed combustion appliances (systems consisting of a
8.4.2 Determine Baseline Depressurization—Determine the
single appliance on a flue that has no draft hood or relief air).
value of the indoor-outdoor pressure differential with all
8.6.2 Compare the maximum pressure differentials (con-
continuous and intermittent house fans off, in accordance with
tinuous and intermittent) with depressurization limits for each
the house conditions established in 8.3 (see Table 1). Pressure
vented, fuel-burning appliance in the dwelling.
differences may be quite variable, especially under windy
8.6.3 Thismethodprovidesresultsinapassorfailform.For
conditions; thus, an average of several values should be used.
example, if the intermittent pressure limit is 5 Pa (this limit
8.4.3 Turn on Furnace Blower—Operate the blower at
varies with appliance fuel and venting configuration) and the
maximumspeedifitcanbeswitchedonindependentlyofother
measured intermittent pressure differential is 6 Pa
exhausts. The house depressurization level in the appliance
depressurization, then the house fails the test and is considered
room, relative to outdoors, should be assessed with the door to
to be spillage-prone.
the appliance room (if any) both open and closed. The door
8.6.4 The method provides pass or fail results without
position that results in the highest level of house depressuriza-
operation of any vented combustion appliances: thus, their
tion should be used for the remainder of the test. If the furnace
ability to tolerate, or overcome, the house depressurization
blowerdoesnotincreasethehousedepressurization,turnitoff.
induced during the test is not assessed.
8.4.4 Turn on Combined Supply and Exhaust Ventilators—
8.6.5 The pass or fail criteria may not be appropriate for all
Operate each of these devices at its highest setting and check
types of homes, appliances, venting systems, and climates.
if house depressurization increases. If it does, leave the device
8.6.6 Resultsofthistestforaparticularhomemayvarywith
running; otherwise, turn it off.
weather conditions (temperature and windspeed). The exact
8.4.5 Turn on Continuous Air Exhaust Systems—Turn on
nature of relationship between test results and weather condi-
such devices intended for continuous use, such as subslab
tions is not fully understood at present.
ventilation systems.
8.4.6 Turn on Continuous Air Supply Systems—Operate any 8.7 Technician and Test Time—About 30 to 40 min of
of these devices intended to operate throughout the heating technician or testing time is required, including the time for
season. setting up equipment.
E1998 − 11 (2018)
9. Downdrafting Test (4) 9.4.3.2 Turn on the furnace blower and all exhaust fans
(bathroom exhausts, kitchen range fan if exhausted to out-
9.1 Summary of Procedure—The test is conducted under
doors).
closed-house conditions (exterior doors, windows, fireplace or
9.4.3.3 Set the clothes dryer to air option (if available) or to
woodstovedampers,orboth,closed).Ideally,thetestshouldbe
the lowest heat setting: set timer for 30 min and start the dryer.
performed during a period of low wind speeds (less than 2 m/s
9.4.3.4 Open wood fireplace damper, if applicable, and
or 5 mph). Interior doors on perimeter rooms that do not
simulate its operation with a camping stove. Ensure that the
containexhaustdevicesareopen.Thewaterheaterandfurnace
stove is secured in its place. Wait up to 5 min to verify that the
remain off throughout the test. After all continuous fans and
fireplace chimney is venting.
intermittent exhaust devices (including a fireplace simulator or
9.4.3.5 Turn on any gas log(s) located in a fireplace after
a gas-log fireplace) are turned on, downdrafting is assessed
opening the fireplace damper.
visually with a flame or smoke pencil.
9.4.3.6 For a worst-case depressurization level, close all
9.2 Equipment Needed—Flame lighter or smoke pencil for
interior doors to perimeter rooms that do not contain any
visual indication of downdrafting, temperature sensor for
exhaust devices. Then choose the condition of furnace blower
measuring vent temperature, camping stove to simulate fire-
off versus on, and door nearest the appliance open versus
place operation are needed.
closed, that maximizes house depressurization.
9.3 House Conditions—Keep the house in its (winter)
9.4.4 Verifythatthewaterheaterandfurnaceremainoffand
closed configuration as given in Table 2. Tables 1 and 2 are
that the common-vent temperature is near (that is, within 3 to
similar except for the position or status of interior doors, the
6°Cor5to10°F)thetemperatureinthemechanicalroom.For
damper of the make-up air supply, and subslab or subfloor
this verification, a temperature sensor can be attached to the
ventilation systems. The conditions in Table 2 are intended to
outside of a metal common vent (or to the outside of a vent
represent a reasonable-worst-case scenario. For a worst-case
connector in close proximity to a masonry chimney).
depressurization level, add the step given in 9.4.3.6. Subslab
9.4.5 Assess downdrafting through the water heater vent
ventilation systems are left in the condition set by occupants to
connector at the draft hood with a visual (smoke or flame) test.
minimize radon exposure.
9.4.6 Assessdowndraftingthroughthefurnaceventconnec-
tor with a visual (smoke or flame) test by checking at the
9.4 Procedures:
furnace draft hood. If the furnace is an induced-draft type this
9.4.1 Turn down furnace/boiler and water heater thermo-
test can be omitted.
stats.
9.4.2 Allow time for cooling the common vent if either of 9.4.7 Return water heater and furnace thermostats to occu-
pant settings.
these appliances was operating recently.
9.4.3 Set up continuous fans and intermittent exhaust de-
9.5 Data Reporting:
vices.
9.5.1 Note the configuration during the test for each item in
9.4.3.1 Leave on any continuous air supply or exhaust
Table 2.
systems that are normally used by the occupants. Do not turn
9.5.2 Note the outdoor temperature and windspeed at the
onawhole-housefanifitisnormallyusedwithwindowsopen.
time of the test by calling the telephone number that provides
recorded messages of local weather conditions.
A
9.5.3 For each vent connector (if applicable), note whether
TABLE 2 Initial House Conditions for Downdrafting and
Backdrafting Tests (4)
downdrafting has been observed.
House Feature Configuration
9.6 Results and Interpretation:
Windows Close
9.6.1 The results of this test are in yes or no form, that is,
Exterior doors Close
Interior doors to basement Open
whether or not downdrafting has been observed.
Doors on an enclosed mechanical room Open
9.6.2 These results are specific to the venting system, house
Interior doors on perimeter rooms not Open
containing exhaust devices and outdoor conditions under which the tests are conducted.
Make-up air supply for mechanical room Leave as is
9.6.3 Currently, there is no technique available for extrapo-
Woodstove or fireplace No fire: close manual
lating test results to other conditions, such as a different
dampers
Furnace and water heater Turn down thermostats
outdoor temperature or windspeed, or both.
Furnace blower Off
9.6.4 Resultsofthistestforaparticularhomemayvarywith
Floor drains Fill with water
weather conditions (temperature and windspeed). The exact
Exhaust and supply fans Off
Ventilating and air-moving devices Off
nature of relationship between test results and weather condi-
Clothes dryer Off
tions is not fully understood at present.
Attic hatch Close
Broken windows or other short-term openings Tape over
9.7 Technician and Test Time—This method requires a
Subslab ventilation fans or subfloor ventilation Leave as is
minimum amount of time, except for cooling the vent before
systems for soil-gas control
tests. There is no equipment to set up except for the fireplace
A
These conditions are intended to represent a reasonable-worse-case scenario.
Foraworst-casedepressurizationlevel,aftersettingtheaboveconditionscloseall simulator in the case of a fireplace. The time required to set
interior doors to perimeter rooms that do not contain any exhaust devices. Then
house conditions to those specified in Table 2 and to conduct
choose the condition of furnace blower off versus on, and door nearest the
the test(s) requires about 10 to 20 min, not including time for
appliance open versus closed, that maximizes house depressurization.
coolingthevent.Thetimerequiredtocooltheventwilldepend
E1998 − 11 (2018)
on the capacity of exhaust devices and the type of chimney off versus on, and door nearest the appliance open versus
(masonry versus metal): cooling the vent with exhaust devices closed, that maximizes house depressurization.
may require 15 to 30 min or more. The cooling time often can
10.4.4 Verify that the water heater and furnace remain off
be shortened considerably by using a blower-door fan. The
and that the common-vent temperature is near (that is, within 3
technician and test time are the same for this method.
to 6 °C, 5 to 10 °F) the temperature in the mechanical room.
For this verification, a temperature sensor can be attached to
10. Appliance Backdrafting Test (see CAN/CGSB-51.71
the outside of a metal common vent (or to the outside of a vent
and Refs. 4 and 10)
connector in close proximity to a masonry chimney).
10.1 Summary of Procedure—The test is conducted under
10.4.5 Verify that the water heater’s pilot light is on. Turn
closed-house conditions (exterior doors, windows, fireplace or on the water heater by setting the thermostat to its highest
woodstovedampers,orboth,closed).Ideally,thetestshouldbe
setting and turning on a hot water faucet. Note the exact time
performed during a period of low wind speeds (less than 2 m/s when the water heater turns on.
or 5 mph). Interior doors on perimeter rooms that do not
10.4.6 Assess water heater drafting with a visual (smoke or
contain exhaust devices are open.After all continuous fans and
flame) test. Perform the test at the water heater draft hood until
intermittent exhaust devices (including a fireplace simulator or
venting is established. Note the exact time when venting is
a gas-log fireplace) are turned on, the water heater is operated
established. Terminate the test if venting is not established
for a period such as 5 min. (The test described below uses a
within 5 min. Return the water heater thermostat to its lowest
time period of 5 min which is somewhat arbitrary: other time
setting and turn off the hot water faucet. Verify that water
periods such as 3 min or 10 min have been used.) Backdrafting
heater and furnace pilot lights are on.
is assessed visually with a flame lighter or smoke pencil. The
10.4.7 Coolventtoatemperaturethatisnear(thatis,within
vent is cooled and the procedure is repeated for the furnace.
3to6°Cor5to10°F)thetemperatureinthemechanicalroom
by leaving the exhaust fans and appliances on for at least
10.2 Equipment Needed—Flame lighter or smoke pencil for
5 min. Use a blower door to cool the vent if available.
visual indication of backdrafting, temperature sensor for mea-
10.4.8 Verify that the furnace’s pilot light (if any) is on.
suring vent temperature, and camping stove to simulate fire-
Turn on the furnace by setting its thermostat to 30 °C (85 °F).
place operation are needed. If a blower door is available, it can
Note the exact time when the furnace burner ignites.
be used to cool vents more rapidly between multiple tests of
10.4.9 Assess furnace drafting with a visual (smoke or
backdrafting (masonry chimneys will take a considerably
flame) test by checking at the furnace draft hood. If the furnace
longer time to cool than metal chimneys).
is an induced-draft type then assess drafting at the water heater
10.3 House Conditions—Keep the house in its (winter)
draft hood. Perform a visual test until venting is established.
closed configuration as given in Table 2, which is intended to
Note the exact time when venting is established. If backdraft-
represent a reasonable-worst-case scenario. For a worst-case
ing occurs and persists beyond 5 min, terminate the test.
depressurization level, add the step in 10.4.3.6.
10.4.10 Return water heater and furnace thermostats to
10.4 Procedures:
occupant settings.
10.4.1 Turn down furnace/boiler and water heater thermo-
10.5 Data Reporting:
stats.
10.5.1 Notetheconfigurationduringthetestforeachitemin
10.4.2 Allow time for cooling the common vent if either of
Table 2.
these appliances was operating recently.
10.5.2 Note the outdoor temperature and windspeed at the
10.4.3 Set up continuous fans and intermittent exhaust
time of the test by calling the telephone number that provides
devices.
recorded messages of local weather conditions.
10.4.3.1 Leave on any continuous air supply or exhaust
10.5.3 For each appliance, record the duration of backdraft-
systems that are normally used by the occupants. Do not turn
ing if a draft is established within 5 min.
onawhole-housefanifitisnormallyusedwithwindowsopen.
10.6 Results and Interpretation:
10.4.3.2 Turn on the furnace blower and all exhaust fans
(bathroom exhausts, kitchen range fan if exhausted to out- 10.6.1 The results of this test are in yes or no form, that is,
doors). whether or not venting is established within 5 min (or the
nominal cycle time for the appliance) after the appliance is
10.4.3.3 Set the clothes dryer to air option (if avail
...