August 2005

Test data shows outdoor boilers are inefficient and polluting

Here at, we have for several years been critical of smoky outdoor boilers and their manufacturers for misleading buyers with dubious performance claims. But there had been so little testing done that in the minds of potential buyers it was our word against the manufacturer's.

Now the New York State government has released a damning report on outdoor wood boilers (OWB), revealing their poor performance and exposing manufacturers' claims as mostly bogus. Here are some quotes from Smoke Gets in Your Lungs: Outdoor Wood Boilers in New York State:

"We found that while OWBs are advertised as a clean and economical way to heat one’s house and water, OWBs may be among the dirtiest and least economical modes of heating, especially when improperly used."

"Conventional wood stoves manufactured prior to 1992, which were not airtight and had no pollution controls, generated an average of 18.5 grams PM 2.5 per hour, whereas the newer EPA-certified wood stoves averaged about six grams per hour. In similar tests, OWB emissions ranged from 18 to147 grams PM 2.5 per hour and averaged about 72 grams per hour."

"The EPA has found heating efficiencies of about 54 percent for conventional wood stoves, and 68 to 72 percent for EPA-certified wood stoves. In comparison, data obtained from manufacturers on tests conducted on OWBs found that they have heating efficiencies ranging from 28 to 55 percent, with an average of 43 percent."

If you are considering the purchase of an outdoor boiler system, you owe it to yourself to read this report first.