Building America Expert 

Meeting: Combustion Safety

L. Brand 

Partnership for Advanced Residential Retrofit

March 2013
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iii

Building America Expert Meeting: Combustion Safety

Prepared for:

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program 

Office of Energy Efficiency and Renewable Energy

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

 

Prepared by: 

Larry Brand 

Partnership for Advanced Residential Retrofit 

(Gas Technology Institute) 

1700 South Mount Prospect Road 

Des Plaines IL 60018 

NREL Technical Monitor: Stacey Rothgeb

Prepared under Subcontract No. KNDJ-0-40346-00

March 2013 
iv

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v 

Contents

List of Tables .............................................................................................................................................. vi

Definitions.................................................................................................................................................. vii

Acknowledgments ................................................................................................................................... viii

1 Meeting Overview ................................................................................................................................. 1

1.1 Title ..................................................................................................................................1

1.2 Who ..................................................................................................................................1

1.3 What ..................................................................................................................................1

1.4 Where ..................................................................................................................................1

1.5 When ..................................................................................................................................1

1.6 Why ..................................................................................................................................1

1.7 How ..................................................................................................................................2

2 Meeting Recap ...................................................................................................................................... 6

2.1 Welcome ..............................................................................................................................6

2.2 Presentation 1—National Fuel Gas Code Coverage ............................................................6

2.2.1 Presentation Title .....................................................................................................6

2.2.2 Key Points ................................................................................................................6

2.3 Presentation 2—ASHRAE 62.2 Ventilation Requirements.................................................7

2.3.1 Presentation Title .....................................................................................................7

2.3.2 Key Points ................................................................................................................7

2.4 Presentation 3—Building Performance Institute Combustion Safety Procedures ...............8

2.4.1 Presentation Title .....................................................................................................8

2.4.2 Key Points ................................................................................................................8

2.5 Presentation 4—Field Research and Building Performance Institute Guidelines ...............8

2.5.1 Presentation Title .....................................................................................................8

2.5.2 Key Points ................................................................................................................9

2.6 Presentation 5—House Airtightness and Combustion Safety .............................................9

2.6.1 Presentation Title .....................................................................................................9

2.6.2 Key Points ..............................................................................................................10

2.7 Presentation 6—Long-Term Monitoring of Residential Water Heaters ............................10

2.7.1 Presentation Title ...................................................................................................10

2.7.2 Key Points ..............................................................................................................10

2.8 Presentation 7—Review and Assessment of Combustion Safety Diagnostics ..................11

2.8.1 Presentation Title ...................................................................................................11

2.8.2 Key Points ..............................................................................................................11

3 Summary ............................................................................................................................................. 13

4 Meeting Outcomes and Next Steps .................................................................................................. 15

5 Bibliography........................................................................................................................................ 16

Appendix A: Meeting Slides..................................................................................................................... 17

Presentation 1—National Fuel Gas Code Coverage ................................................................17

Presentation 2—ASHRAE 62.2 Ventilation Requirements.....................................................18

Presentation 3—Building Performance Institute Combustion Safety Procedures ...................19

Presentation 4—Field Research and Building Performance Institute Guidelines ...................20

Presentation 5—House Airtightness and Combustion Safety .................................................21

Presentation 6—Long-Term Monitoring of Residential Water Heaters ..................................22

Presentation 7—Review and Assessment of Combustion Safety Diagnostics ........................23

Appendix B: Meeting Flyer....................................................................................................................... 24
vi 

List of Tables

Table 1. Presenters, Affiliations, and Job Titles ...................................................................................... 3

Table 2. In-Person Participants ................................................................................................................. 4

Table 3. Remote Participants..................................................................................................................... 4

Table 4. Agenda........................................................................................................................................... 5

Unless otherwise indicated, all tables were created by PARR. 
vii 

Definitions

ACH Air changes per hour

ACH50 Air changes per hour at 50 pascals

AFUE Annual fuel utilization efficiency

AGA American Gas Association

ANSI American National Standards Institute

BA Building America

BPI Building Performance Institute

CO Carbon monoxide

DOE U. S. Department of Energy

FSEC Florida Solar Energy Center

GTI Gas Technology Institute

LBNL Lawrence Berkeley National Laboratory 

NFGC National Fuel Gas Code

NREL National Renewable Energy Laboratory

Pa Pascal

PARR Partnership for Advanced Residential Retrofit

RESNET Residential Energy Services Network
viii

Acknowledgments

PARR would like to thank all the attendees for their participation in the meeting, especially the 

panel members. PARR also thanks Jeff Tuttle and Alex Chavez from CPS Energy for hosting the 

meeting and for their hospitality and Kristy Usnick from the National Renewable Energy 

Laboratory for assistance with the webinar.
1 

1 Meeting Overview

1.1 Title 

This expert meeting was called The Best Approach to Combustion Safety in a Direct Vent 

World. 

1.2 Who 

The Partnership for Advanced Residential Retrofit (PARR) invited industry experts from 

Building America (BA) teams, manufacturers, HVAC installers, national laboratories, the U.S. 

Department of Energy (DOE), and PARR partners. Twenty-four experts participated in the 

meeting. 

1.3 What 

The objectives of this expert meeting were to identify gaps and barriers that need to be addressed 

by future research, and to develop data-driven technical recommendations for code updates so 

that a common approach for combustion safety can be adopted by all members of the building 

energy efficiency and code communities.

1.4 Where

This meeting was hosted by CPS Energy in San Antonio, Texas. 

1.5 When

The meeting took place on Thursday June 28, 2012, from 9:00 a.m. to 3:00 p.m. Central Daylight 

Saving Time. 

1.6 Why

The DOE BA program focuses on reducing energy consumption in the nation’s housing stock 

through smart integration of energy efficient design and upgrades. The target is 30%–50% 

energy savings captured through the application of many measures, including reduction in air 

infiltration, equipment upgrades, smart controls, and thermal envelope improvements. 

Combustion safety testing is an important part of the test-in and test-out process in new 

construction and retrofit (upgrade) projects when direct vent appliances are not used and houses 

are being tightened to reduce energy losses through air infiltration. Where combustion safety 

testing identifies excessive spillage or continuous back-drafting, remedial measures are required.

Members of building science community hold many different opinions about the best overall 

remediation method (testing to verify performance or replacement of the appliance) and the 

proper test procedures to use to verify combustion safety for appliances equipped with draft 

hoods. Practitioners and codes differ in the recommendations for two variables: the level of 

home depressurization and the time required for cold vent establishment pressure. 

In addition, statistics on incidents and data collected from the field have not supported stringent 

testing requirements.

The meeting’s objectives were as follows: 

• Evaluate the pros and cons of upgrading to direct vent appliances, especially when 

existing appliances and/or venting mechanisms do not meet current code or are near their 

end of life. 
2 

• Investigate current Building Performance Institute (BPI) and Residential Energy Services 

Network (RESNET) practices for combustion safety testing in the field. 

• Review the International Code Council and National Fire Protection Association 

(NFPA)/American National Standards Institute (ANSI) code requirements. 

• Evaluate data collected from the field in several programs. 

• Discuss ongoing research on this topic. 

This discussion identified gaps and barriers that need to be addressed by future research. In 

addition, the participants developed data-driven technical recommendations for code updates that 

will allow a common approach to be adopted by all members of the building energy efficiency 

and code communities. 

The following research questions were addressed:

• What are the risks associated with continued use of appliances that are near their end of 

life or venting systems that do not meet the current mechanical codes?

• What data have been collected and what additional data need to be collected to support 

the analysis that will lead to the development of a common standard for combustion 

safety?

• How do field practices agree or disagree with the code coverage? 

• What low- or no-cost options are currently available that satisfy the need for combustion 

safety in homes with low infiltration?

1.7 How

Expert meetings are designed to be an interactive experience, where all participants contribute in 

substantive ways. Representatives from PARR, other BA teams, the national laboratories, as well 

as other panel members, were chosen to discuss code coverage, field practices, previous 

research, and ongoing research. Table 1 lists the presenters, their affiliations, and their topics. 

The appendix to this report contains the first page of each presenter’s slides. Full presentations 

and the webinar recording are available from PARR and accompany this report on the NREL 

website at http://www1.eere.energy.gov/buildings/residential/ba_meetings.html. 
3 

Table 1. Presenters, Affiliations, and Job Titles

Presenter Company Title Role

Larry Brand Gas Technology 

Institute (GTI) R&D Manager

R&D manager at GTI and a principal 

investigator for PARR. Brand 

developed and led the expert meeting.

Paul Cabot 

American Gas

Association 

(AGA)

Administrator, 

National Fuel Gas 

Code 

Administrator for the National Fuel 

Gas Code at the AGA. He presented 

the National Fuel Gas code 

requirements for combustion safety. 

Dan Cautley Energy Center of 

Wisconsin 

Senior Project 

Manager

Senior project manager at the Energy 

Center of Wisconsin in Madison. He 

presented a perspective on the issue 

from past research that included longterm monitoring of residential water 

heaters.

Jim 

Cummings

Florida Solar 

Energy Center 

(FSEC)

Program Director, 

Buildings 

Research

Program director for buildings 

research at FSEC and an ASHRAE 

Fellow. He presented a perspective on 

house airtightness, ventilation, and 

combustion safety. 

Jim 

Fitzgerald

Minnesota Center 

for Energy and the 

Environment 

Senior Building 

Analyst

Senior building analyst for the 

Minnesota Center for Energy and the 

Environment. He presented 

information on the background of 

BPI requirements from field research.

Paul 

Francisco

University of 

Illinois Sustainable 

Technology Center

Research 

Specialist

Research specialist at the University 

of Illinois. His research focuses on 

field evaluations of energy efficiency 

and indoor air quality. He presented 

the current ASHRAE 62.2 

requirements and implications for 

combustion safety. 

John Jones BPI

National 

Technical 

Director

BPI’s national technical director. He 

presented the BPI combustion safety 

testing guidelines and the reasons 

behind some of the recommendations. 

Vi Rapp

Lawrence 

Berkeley National 

Laboratory 

(LBNL)

Postdoctoral 

Fellow

Postdoctoral fellow in the 

Environmental Energy Technology 

Division at LBNL. She presented 

LBNL’s recent work for the 

California Energy Commission on 

venting and discussed an upcoming 

project.
4 

Table 2 names participants who did not present at the meeting.

Table 2. In-Person Participants

Table 3 lists the participants who joined the meeting by phone. 

Table 3. Remote Participants

Attendees Organization

Ron Caudle Southern California Gas Company

Terry Clausing Drysdale & Associates, Inc.

David Delaquila Air Conditioning, Heating, and Refrigeration Institute

Ann-Marie Dougan Vectren

Ronnie Frazier Atmos Energy

Gary Heikkinen Northwest Natural Gas

Pat Huelman University of Minnesota

David Mallay National Association of Home Builders Research Center

Andrea Papageorge AGL Resources

Jim Ranfone AGA

Brett Singer LBNL

Jason Stanek Omaha Municipal Utility District

Elizabeth Tate American Public Gas Association

Kristy Usnick NREL

Eric Wilson NREL

Jon Winkler NREL

Attendees Organization 

Ren Anderson National Renewable Energy Laboratory (NREL)

Alex Chavez CPS Energy San Antonio 

Dane Christensen NREL

Zach Merrin University of Illinois Sustainable Technology Center

Nick Mittereder IBACOS

Bill Rose University of Illinois Sustainable Technology Center

Stacey Rothgeb NREL

Jeff Tuttle CPS Energy San Antonio 

Craig Wray LBNL
5 

Table 4 gives the meeting’s agenda.

Table 4. Agenda

Time Presenter Topic

9:00 Larry Brand Welcome, Introductions, Objectives

9:30 Paul Cabot National Fuel Gas Code Coverage

10:00 Paul Francisco ASHRAE 62.2 Ventilation Requirements

10:30 John Jones BPI Combustion Safety Procedures

11:15 Larry Brand Gaps and Barriers in the Codes; Opportunities to 

Harmonize

11:45 Jim Fitzgerald Field Research and BPI Guidelines

12:15 Lunch

1:00 Jim Cummings House Airtightness and Combustion Safety

1:30 Dan Cautley Long-Term Monitoring of Residential Water 

Heaters

2:00 Vi Rapp LBNL Research; California Energy Commission

Project on Combustion Safety

2:30 Larry Brand Gaps and Barriers in the Research

3:00 Close
6 

2 Meeting Recap

2.1 Welcome 

Larry Brand welcomed the panel and participants and introduced the topic of the expert meeting. 

He indicated that the webinar was presented by the PARR team on behalf of DOE’s BA

program. He mentioned that the speakers would focus on combustion safety from several 

perspectives and then work to identify gaps and barriers in the research. He also suggested that 

the team should identify opportunities to harmonize the codes where they differ.

Brand introduced each speaker in turn. Questions and responses are included in the key points 

for each presentation, which follow. 

2.2 Presentation 1—National Fuel Gas Code Coverage

Paul Cabot presented a perspective on the topic from the gas industry and the National Fuel Gas 

Code (NFGC). 

2.2.1 Presentation Title

Fuel Gas Appliances Combustion Air and Inspection, National Fuel Gas Code ANSI Z223.1 and 

NFPA 54 

2.2.2 Key Points

The NFGC has been an ANSI standard since 1974. It establishes combustion air requirements for 

natural gas appliances across most of the United States. All listed appliances refer to the NFGC, 

which has dual listing as ANSI Z223.1 and NFPA 54. The same combustion air requirements are 

in all the model fuel codes (the two just mentioned and the Uniform Plumbing Code). 

There are two basic methods for determining combustion air for appliances: the standard method 

and the alternate method. The standard (required volume) method is based on an infiltration level 

of 0.5 ACH in the house. The alternate method (known as the air infiltration rate method) is used 

where the known infiltration rate is less than 0.4 ACH. Another method is prescribed for air 

taken from the outdoors. Engineered and mechanical methods are also permitted. The code 

contains many restrictions and requirements relating to appliance installation. 

Venting tables are given for Category I appliances so the proper vent performance is achieved. 

Manufacturers’ installation instructions are to be consulted for non-draft type appliances. A 

recommended procedure is provided for the safety inspection for furnaces and boilers in Annex 

G. This procedure includes checking the draft after 5 min of operation with doors, windows, and 

fireplace dampers closed.

Key takeaways from this presentation follow: 

• The NFGC is the recognized ANSI code and its combustion air and venting requirements 

are the basis for codes adopted by most U.S. jurisdictions for installation and operation of 

gas appliances.

• Combustion air guidelines were revised in 2001 to account for lower infiltration rates in 

newer homes. It might be appropriate to revisit these assumptions as houses are built 

tighter (gap). 

• Annex G in the code (safety inspection) applies only to furnaces and boilers and it should 

be expanded to include water heaters (gap). 
7 

• The draft spillage test in Annex G is conducted for each appliance. The test is first

conducted with each appliance operating separately and is then repeated with all 

appliances operating in the same location. The written procedure is somewhat 

vague (gap).

• NFGC and ASHRAE 62.2 should reference each other with regard to combustion air 

requirements and vent safety testing (gap). 

2.3 Presentation 2—ASHRAE 62.2 Ventilation Requirements

Paul Francisco presented the current ASHRAE 62.2 residential ventilation requirements and 

implications for combustion safety. 

2.3.1 Presentation Title

ASHRAE 62.2—Ventilation and Combustion Safety 

2.3.2 Key Points

ASHRAE Standard 62.2 (an ANSI standard) addresses the need for ventilation to achieve 

acceptable indoor air quality in increasingly tight houses in the United States. Key objectives are

to ensure that occupants express no dissatisfaction with respect to odor and irritation and, at the 

same time, to maintain an indoor environment in which contaminants are below levels that create

a health risk. A calculation method is used to determine how much mechanical ventilation is 

required. Ventilation can be provided by several methods including exhaust-only, supply-only, or 

balanced (energy recovery ventilators or other means). Typically, smaller (ventilation) fans do 

not produce significant levels of depressurization that can cause combustion safety issues, but 

poorly sealed HVAC ducts, kitchen fans, dryers, and fireplaces can be major contributors. 

Key takeaways from this presentation follow: 

• Appliances should first be installed to code to minimize depressurization-induced backdrafting.

• Typically, appliances can handle 5 Pa of depressurization, but this number needs to be 

verified (gap). 

• The largest contributors to depressurization are leaky HVAC ductwork and the larger 

exhaust systems—such as kitchen fans, dryers, and fireplaces. 

• There are several approved methods to comply with ASHRAE 62.2. E—xhaust-only 

ventilation is not required. 

• Field data on exhaust fan flow rates and house depressurization level are needed to verify 

assumptions (gap). 

• A risk assessment tool to determine if exhaust-only ventilation is inappropriate for a 

particular house is needed to avoid creating an issue with atmospheric appliances or 

fireplaces (gap).

• Organizations with combustion safety testing protocols and other combustion air code 

language should reconcile their different approaches to meet the needs of all 

stakeholders. Of particular importance is a common approach to addressing the full range 

of factors that can influence proper venting, given the variety of conditions found in older 

homes (gap). 
8 

2.4 Presentation 3—Building Performance Institute Combustion Safety 

Procedures

John Jones gave a presentation on BPI’s combustion safety test procedures. 

2.4.1 Presentation Title

BPI Combustion Safety Testing Requirements, Raising the Bar in Home Performance 

Contracting, Combustion Safety in a Direct Vent World 

2.4.2 Key Points

About two-thirds of owner-occupied homes in the United States are at least 25 years old and 

were built before modern mechanical and energy codes were put into place. These homes have 

likely had numerous modifications, and some equipment could have been installed incorrectly or 

might have deteriorated from age or improper use. Testing these systems is necessary to ensure 

that improvements can be done safely and that the building is safe after the work is complete.

BPI conducts preliminary and post-retrofit combustion safety inspections whenever there is a 

change to the building envelope or heating system as a part of the work scope. Carbon monoxide 

(CO) testing of undiluted flue gases is performed for every appliance (including direct vent 

appliances). Draft and spillage are evaluated for atmospherically vented appliances with the 

house set up for worst-case depressurization. Technicians are given a recommended test guide to

that includes information on setting up worst-case depressurization, measuring spillage from the 

draft hood, and measuring CO action levels.

Key takeaways from this presentation follow: 

• None of the BPI standards supersede codes or manufacturers’ installation instructions. 

• If BPI standards are too stringent, there is a mechanism to change them. Pre-and posttesting of all appliances, however, must be completed. 

• The NFGC tests for spillage after 5 min of operation and the BPI test is conducted after 1 

min of operation. The NFGC and BPI tests are based on different data sets and there is an 

opportunity to harmonize (gap). 

• The CO limit for appliances is based on a Colorado study, not the ANSI appliance 

certification testing. There might be an opportunity to harmonize, but more testing is 

required (gap). 

• BPI recommends more testing in the field on actual installations in actual homes. 

Manufacturers should be a part of the field testing to set performance limits for 

certification (gap).

2.5 Presentation 4—Field Research and Building Performance Institute

Guidelines

Jim Fitzgerald gave a presentation on the basis for some of the BPI combustion safety guidelines 

and other research from the field. 

2.5.1 Presentation Title

Testing Protocols & Results: Airport Sound Program Experience and BPI/RESNET 

Development 
9 

2.5.2 Key Points

Air tightening of existing homes can affect combustion appliance safety. A Minnesota airport 

sound reduction study in 3,000 houses reduced infiltration, on average, from 7.8 ACH50 to 5.4 

ACH50, creating unsafe conditions in many homes. Combustion safety tests were added to the 

retrofit protocol to ensure that safety issues were addressed. CO and worst-case spillage tests 

were included. 

Many CO problems are related to poor maintenance and tuning, not design. Vents need to be 

checked against the NFGC sizing guidelines as a part of the safety test. Many vents have been

poorly installed. Following the NFGC yields systems that are very likely to vent properly. 

Maintenance and tuning at a cost of $100 to $300 per appliance is less expensive than 

replacement and can reduce CO levels significantly. 

More than 5 Pa of depressurization reverses most vent systems. That is equivalent to a dryer 

operating in a closed house tested at 450 cubic feet per minute at 50 Pascals of depressurization. 

Water heaters spill more in warmer weather than colder weather because of the physics of 

buoyancy; a warmer climate solution is to install water heaters in a garage or mechanical closet, 

but that is not a reasonable solution for cold climates. 

Unbalanced central returns in the HVAC system can be a significant cause of depressurization. 

Key takeaways from this presentation follow: 

• The NFGC venting tables are not used properly in the field (a venting portable computer 

application would be useful). The industry needs a better way to check the existing vent 

for compliance (gap).

• The NFGC should furnish depressurization guidance followed by a pass/fail spill test

(gap). In the airport study, even if the vents were sized properly, 82% of atmospheric 

vents failed the spillage test at 5 Pa of depressurization – indicating an extreme 

condition. 

• More field data are needed to determine the effect of ambient temperature on 

depressurization, whether to use 5 min or 1 min for the spillage test, appropriate door 

position, and the impact of kitchen ventilation (gap). 

• The only way to ensure absolute safety is to require direct vent natural gas appliances 

and seal systems from the house. 

• The risk associated with failing the combustion safety test needs to be better 

characterized (gap). The risks associated with tightening houses could outweigh the 

benefits.

2.6 Presentation 5—House Airtightness and Combustion Safety

Jim Cummings presented his work on house airtightness and combustion safety with a focus on 

house ventilation. 

2.6.1 Presentation Title

Combustion Safety Concerns and Energy Savings in Very Airtight Residences
10 

2.6.2 Key Points

For very tight homes, further tightening will save very little energy (payback can exceed 50 

years), but tightening envelopes can create substantial problems in terms of combustion safety 

and the risk of very poor indoor air quality if mechanical ventilation systems fail. Sealed 

combustion systems largely address atmospheric appliance issues where –5 Pa of 

depressurization creates back-drafting at the vent hood. Mechanical ventilation systems can fail 

in many ways: motors can burn out, belts can break, filters might not be maintained, and 

occupants could turn off the system. Very poor indoor air quality can result. The economics of 

decreasing infiltration rates are poor when energy recovery ventilators are required - going from 

an ACH50 of 5 to 1 saves $65/year in energy costs in Florida (net of energy recovery ventilator 

fan power), but the energy recovery ventilator costs $135/year of life (assuming $100 per year 

for maintenance). This results in a negative savings. Even without the annual maintenance cost, 

payback is 50 years. The proposal is to limit house leakage levels to a minimum of 5 ACH50 for 

climate zones 1–3, 4 ACH50 for climate zones 4–5, and 3 ACH50 for climate zones 6–7. 

Key takeaways from this presentation follow: 

• Tightening homes to extreme levels saves very little energy (payback can exceed 50 

years), but can create substantial problems in terms of combustion safety and risk of very 

poor indoor air quality if mechanical ventilation systems fail. Even in cold climates (e.g., 

Chicago), the payback period is very long and the risks are very real. 

• The proposal is to limit house leakage levels to approximately 5 ACH50 for climate 

zones 1–3, 4 ACH50 for climate zones 4–5, and 3 ACH50 for climate zones 6–7. 

• The actual annual energy savings associated with tightening homes below these limits 

must be determined by field data collection and analysis along with measuring key 

components of indoor air quality (gap). 

2.7 Presentation 6—Long-Term Monitoring of Residential Water Heaters

Dan Cautley presented the results of research done on field monitoring of residential water 

heaters.

2.7.1 Presentation Title

Combustion Safety: Some Context and Water Heater Monitoring Results

2.7.2 Key Points

Of the 250,000 accidental deaths in the United States each year, about 183 are attributable to CO 

deaths from consumer products of all types. The estimated deaths from hazards including 

secondhand smoke and radon far exceed those from CO poisoning. Cold vent establishment 

pressure is the maximum depressurization at which proper venting is established when the vent 

starts from a cold condition. That pressure can vary significantly according to the study cited. 

Vent sizing might be more important than typically assumed. In a study, vents sized at 88% of 

the NFGC requirement on average for furnaces and 96% on average for water heaters pass the 

spillage test, but systems designed at 65% and 79%, respectively, fail the test. 

There is poor correlation of worst-case testing with performance monitored over time. Spillage 

of up to 2 min is very common while the vent is priming and it is usually harmless. 
11 

In a DOE and Wisconsin Department of Administration-sponsored project, 10 natural draft water 

heaters were monitored along with 11 replacements. Brief vent spillage on startup was very 

common, but positive vent pressure in the off cycle was uncommon. In one home there were 

several flow reversals related to a short chimney and moderate outdoor temperature. No 

significant CO production was recorded. 

Key takeaways from this presentation follow: 

• Existing pass/fail testing is very simplistic, and might not accurately predict performance

under typical operating conditions. The industry needs long-term monitoring of 

appliances under normal operation to determine the frequency of spillage, not just the 1- 

to 5-min test period (gap). 

• The draft hood is the typical spillage site in atmospheric appliances. Using direct 

vent/power vent appliances is one path to eliminating most spillage problems.

• CO alarms should be required to address periodic events not found in the testing, and 

events associated with sources other than vented appliances. 

• More information on human CO exposure and health effects related to spillage needs to 

be gathered (gap).

• More modeling is needed to determine the sensitivity of depressurization and spillage to 

environmental factors and events in the home (gap). 

2.8 Presentation 7—Review and Assessment of Combustion Safety Diagnostics

Vi Rapp presented the results of a recent California Energy Commission project on combustion 

safety and plans for upcoming research. 

2.8.1 Presentation Title

Review and Assessment of Combustion Safety Diagnostics and Related Literature

2.8.2 Key Points

The hazards associated with combustion spillage are acute exposure causing death or 

hospitalization from CO poisoning, acute subcritical health effects, chronic health effects, and 

moisture-related damage including mold. Deaths from furnace and water heater CO poisonings 

are about 32 per year (2005–2007 U.S. average from the Consumer Product Safety Commission), 

fewer than the 37 annual deaths from lightning (2002–2011 average from National 

Oceanographic and Atmospheric Administration). It is not known, however, how often backdrafting produces subcritical hazards. 

Many appliances fail stress testing by back-drafting based on three studies analyzed, but field 

monitoring data do not confirm the result. The correlation between stress testing and 

performance in the field is not known. 

Many gaps in understanding remain: there is no clear indication of the risks of spillage, 

acceptable spillage durations are inconsistent, key physical parameters leading to back-drafting 

are not identified, and the literature does not address the concept that back-drafting and spillage 

are statistical phenomena. A tool that takes these factors into account and yields a risk 

assessment is needed.
12 

Venting can be affected by weather, the design/condition of the vent system, and 

depressurization. 

A draft LBNL report entitled Assessment of Literature Related to Combustion Appliance Venting 

Systems is out for review. 

Key takeaways from this presentation follow: 

• Appliance stress testing and field performance data are inconsistent. The first produces 

many failures and the second results in few incidents. 

• Field research is needed to determine how often back-drafting produces subcritical 

hazards (gap).

• Improving test methods could reduce risk if the correct variables are addressed.

• A Contam model that adds environmental factors associated with vent performance might 

be a good tool for modeling the phenomenon. LBNL is investigating this possibility.

• Test results are needed to determine what remediation can be done in the field to produce 

an acceptable risk (gap).
13 

3 Summary

Larry Brand thanked all the panel members and participants on the phone for their valuable 

contributions. Gaps and barriers identified and key research questions to be addressed are 

included in the key takeaway section for each presenter. Although not all research questions 

were addressed, the following expert advice can be drawn from this meeting:

• What are the risks associated with continued use of appliances that are near end of 

life or venting systems that do not meet the current mechanical codes? 

Data from Cautley indicate that vent systems that are 30% below code requirements will 

cause back-drafting failures, and data from Fitzgerald show that $100 to $300 in tune-up 

costs can reduce high CO levels in an atmospheric furnace to near zero. Clearly cleaning, 

tuning, and correcting vent deficiencies should be done before replacement is considered. 

If house depressurization is more than 5 Pa and only a water heater is present, 

replacement by a powered vent or direct vent appliance should be considered. Higher 

depressurization limits are permitted for an atmospheric furnace/boiler or common vented 

water heater and furnace/boiler.

• What data have been collected and what additional data need to be collected to 

support the analysis that will lead to the development of a common standard for 

combustion safety? 

Data from Cautley, Fitzgerald, Rapp, and others are provided in the slides, showing that 

there is poor correlation between stress tests and field failures. More long-term field data 

in warm and cold climates with a variety of common and single-appliance vent scenarios 

should be collected. An important first step is to identify and correct improper vent sizing 

and installation so only the house depressurization conditions are being studied. 

• How do field practices agree or disagree with the code coverage?

BPI/RESNET inspection practices differ from the NFGC in several important aspects: 

CO action limits, the test time for back-drafting after startup, combustion air zone 

definitions, and worst-case scenarios. Harmonization of the BPI procedures and the code 

would reduce confusion in the field. Also, data from Cautley, Fitzgerald, Rapp, and 

others are provided in the slides, showing that there is poor correlation between stress 

tests and field failures. This indicates a need to correlate field failures and inspection 

practices. 

What low-cost or no cost options are currently available that satisfy the need for combustion 

safety in homes with low infiltration? 

• The vent should be inspected and modified so that it meets the sizing and installation 

requirements in the NFGC.

• The combustion air provisions in the NFGC should be followed. Adding openings or 

removing doors, for example can improve combustion air supply. 

• Appliances should be cleaned and tuned to ensure that they are operating safely.

• Power vented water heaters are available in the market to replace atmospheric gas water 

heaters.
14 

• ASHRAE 62.2 ventilation requirements can be met with systems other than exhaustonly systems.

Direct vent gas-fired equipment is available for replacement where a higher price point is 

supported. As an example, significantly improving the efficiency level of the equipment as an 

energy saving measure would justify a higher cost. 
15 

4 Meeting Outcomes and Next Steps

The feedback from meeting participants was very positive. The results of this meeting will be 

shared at an upcoming BA technical meeting, as appropriate, as well as with gas utilities in an 

upcoming conference. 

This expert meeting featured excellent interactions among the in-person attendees, and PARR 

recommends that future expert meetings should be conducted in person to foster idea exchange 

and collaboration between technical experts in the subject area. 

Research topics identified during the expert meeting and under consideration for 2013 and 

beyond include the following: 

• Identifying differences between BPI/RESNET inspection practices and the NFGC and 

determining opportunities for harmonization 

• Recommending harmonization of ASHRAE 62.2 and the NFGC language to avoid 

confusion in the engineering community and in the field about applying both codes 

• Collecting long-term performance data in the field to identify the correlation between 

stress tests and field performance, depressurization and back-drafting events, backdrafting/spillage and weather, and indoor contaminants and back-drafting

• Conducting a risk assessment to identify the health risks associated with backdrafting/spillage events as they occur in the field. 

• Conducting a failure modes and effects analysis for exhaust recovery/energy recovery 

ventilators to determine the likely failures and their impact on indoor air quality in lowinfiltration homes

• Developing a contamination model to simulate back-drafting events and their effect on 

indoor air quality. 
16 

5 Bibliography

ASHRAE (2010). Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential 

Buildings. ANSI/ASHRAE Standard 62.2-2010. Atlanta, GA: ASHRAE. Accessed November 

27, 2012: http://www.ashrae.org/standards-research--technology/standards--guidelines (available 

for purchase).

International Code Council (2012). National Fuel Gas Code. ANSI Z223.1/NFPA 54. Accessed 

November 27, 

2012: http://www.nfpa.org/catalog/product.asp?PID=5412&order_src=C900&gclid=CNqvgrC57

7MCFegWMgodxwIAaA (available for purchase).
17 

Appendix A: Meeting Slides 

This appendix shows the first page of each presenter’s slides. The full presentations are available 

from PARR and accompany this report on the NREL website: 

http://www1.eere.energy.gov/buildings/residential/ba_meetings.html#expert. 

Presentation 1—National Fuel Gas Code Coverage 

Paul Cabot presented a perspective on the topic from the gas industry and the National Fuel Gas 

Code. 
18 

Presentation 2—ASHRAE 62.2 Ventilation Requirements

Paul Francisco presented the current ASHRAE 62.2 residential ventilation requirements and 

implications for combustion safety. 
19 

Presentation 3—Building Performance Institute Combustion Safety Procedures

John Jones gave a presentation on BPI’s combustion safety test procedures. 
20 

Presentation 4—Field Research and Building Performance Institute Guidelines

Jim Fitzgerald gave a presentation on the basis for some of the BPI combustion safety guidelines 

and other research from the field. 
21 

Presentation 5—House Airtightness and Combustion Safety

Jim Cummings presented his work on house airtightness and combustion safety with a focus on 

house ventilation. 
22 

Presentation 6—Long-Term Monitoring of Residential Water Heaters

Dan Cautley presented the results of research done on field monitoring of residential water 

heaters.
23 

Presentation 7—Review and Assessment of Combustion Safety Diagnostics

Vi Rapp presented the results of a recent California Energy Commission project on combustion 

safety and plans for upcoming research. 
24 

Appendix B: Meeting Flyer
25 
26 
DOE/GO-102013-3808 ▪ March 2013

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.