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Wood Stove efficiency rating

Posted by razl (My Page) on
Mon, Oct 29, 07 at 13:15

I was reading an article from the Jotul site that mentioned "old" stoves with an efficiency rating of 70%-75% with a reduced air supply (as believed the case in most homes) would drop down to 35%-40%. The article went on to say newer stoves achieve up 80%, but only drop to 70%-75% under the same reduced air supply conditions.

What causes this reduced air supply? 1. The air-tightness of new home construction or 2. The closing of the fresh air intake on the stove itself?

Follow-Up Postings:

RE: Wood Stove efficiency rating

Could you link the article in? I'd like to read it as well, maybe then be better able to comment.

RE: Wood Stove efficiency rating

I have a child with allergies and need to get the most "smoke free" stove I can. Does the ratings determine how much output of smoke a stove will have or does it one determine what goes up the chimney?

RE: Wood Stove efficiency rating

A large fire requires alot of air, so, think about what you're doing... you're sucking air out of the interior of your house, blowing it across a fire, and exhausting it up the chimney (meanwhile heating up some metal). That air you're sucking out of the interior of your house has to come from somewhere, so it leaks through the cracks here and there, but the bottom line is that it comes from the outside. Now, if the 'cracks' in your house are well sealed, it's harder for the stove to get that fresh air, so the fire naturally burns different. A stove that has a fresh air tube is the best bet.

RE: Wood Stove efficiency rating

See link below. Then go to the PDF.
Erik99, I understand the physics behind it, but respectfully, that was not my question. I'm asking whether Jotul is referring to the cause of "restriction" to 1)air infiltration thru the cracks in the house or 2)air intake on the stove itself.

Here is a link that might be useful: Wood Burning

RE: Wood Stove efficiency rating

I believe they are referring to a lack of combustion air inside the house - not closing the air intake on the stove.

The reason I think this is that some stove manufacturers offer an option for hook-up to an outside air duct; also some municipalities/building codes require this for installation.

If you want to do additional reading on the subject, go to and You'll find "to duct or not to duct" is pretty controversial.

I think the bottom line is that local building codes always prevail.

Hope this helps.

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