Reputable Information Sources

Listed below are organizations, testing agencies and web sites that have reputable information concerning gas furnaces, heating, calculations, testing methods, etc.




  AGA  American Gas Association
US testing and rating agency for gas-fired
furnaces till 1997. Testing and certification
is now carried out by CSA Group.
Heat Exchanger Test
Formerly called CSA (Canadian Standards Association). In 2012 all CSA operations were brought under the CSA Group moniker.
CSA Group Fact Sheet
ICC International Code Council
Association that publishes the International Building Codes, International Mechanical Codes and International Fuel Gas Code
2012 Int’l
Fuel Gas Code
 ICC International Code Council
Various versions of othe Internation Fuel Gas Code
Fuel Gas

Gas Research Institute
Merged with the Institute of Gas Technology (IGT) in April, 2000 to form GTI, the Gas Technology Institute. Originally published “Three Step Method for Detecting Unacceptable Flue Gas Leakage from Furnace Heat Exchangers” by Douglas W. DeWerth, P.E. (See * note below.)

3 step
IGT Institute of Gas Technology
Merged with GRI to form GTI in April, 2000.
GTI Gas Technology Institute
An Illinois research non-profit, 501(c)(3), whose programs have resulted in nearly 500 products, 750 licenses and more than 1,200 associated patents.
 AHRI AHRI Heat Exchanger Test Procedure for induced draft heat exchangers **See note below. 5 step
ACHR News Checking for Cracked Heat Exchangers  
ACHR News Ventilation and Heat Exchanger Testing  
ACHR News Supplement to ‘Ventilation and
Heat Exchanger Testing’
ACHR News Basics & finer points of troubleshooting gas furnaces

Heat Exchanger Inspection PDF

Very comprehensive report covering many heat exchanger testing methods, tools and chemicals.

ACHR News Red-Tagging a Furnace: Who Is Responsible?  
 ACHR News

Servicing Gas Appliances – Part 1

Servicing Gas Appliances – Part 2

Servicing Gas Appliances – Part 3

 ACHR News Performing Residential Combustion Analysis  

Performing a Combustion Analysis

Excellent article on combustion measurements on natural and induced draft furnaces and combustion analysis of oil burners.

ACHR News Fossil Fuel Heating Equipment:
Principles And Troubleshooting

Hidden Problems Can Cause Carbon Monoxide

Now here is what I’m talking about .. an article that covers many of the hidden dangers that should be checked when operating gas appliances.


Flue Design Is Critical For Furnace Installations

Finally – it’s in print:

“Cracked heat exchangers do not cause carbon monoxide in a home.” 

Read the last paragraph in the article.


My Two Cents: Crooked Contractors Make Me Sick
By Butch Welsch
A reminder that there are crooks in every industry.



* Note:
Dr. DeWerth created a thorough and unique set of test methods and calculations concerning gas furnace heat exchangers. He discusses various methods to measure and calculate flue gas leakage and shows that under current ANSI standards, a 1/4″ hole is about the largest leak that could be considered acceptable.

However, he ignores one major fact. Heat exchangers in modern furnaces are subjected to positive pressure on the exterior of the heat exchanger shell created by the furnace’s indoor blower. The result is that once the blower turns on, there’s no way for the burners to generate enough air pressure to overcome the force created by the blower. In other words, flue gasses cannot pass from inside the heat exchanger to the indoor air stream.

** AHRI Note:
The AHRI 5-step method makes the same mis-guided assumption that a crack or hole or breach in a draft-induced heat exchanger can somehow allow flue gasses to get into the indoor air stream. It does, however, direct the technician to confirm the vent size, firing rate and combustion air needs of the appliance.

Section 4.1 says “Look for a Flame Disturbance” in its opening sentence. This means that air, pushed by the indoor blower, is moving INTO the heat exchanger and causing the burner flames to be “disturbed”.

Section 4.2a says “If there is no measurable difference in the CO in the Return and Supply Air, it is likely the furnace is not leaking CO into the air stream. If the measured value is below 9 ppm, the Occupational Health and Safety Act (OHSA) acceptable maximum, proceed to 4.3.” This section implies that a net difference in CO readings between return-air and supply air should be attributable to the furnace and an indication of a heat exchanger failure.

The faulty logic tries to defy physics.  First, the observation in section 4.1 that a “flame disturbance” is caused by the blower, meaning indoor air is being pushed INTO the heat exchanger. Second, section 4.2a assumes that any CO created by the furnace will somehow “escape” the heat exchanger and push its way into the indoor air stream. This is hard to do considering the draft inducer is creating .3″ to .4″ WC negative pressure inside the heat exchanger at the same time the indoor blower is creating .1″ to .2″ WC positive pressure on the outside of the heat exchanger.



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