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Posted By MnDave,
Nov 13, 2012 at 9:40 PM
I have read more like 50 to 55%.
What he said.
80% is more like for natural gas, and maybe the high end of pellet stoves. 70% is more what they use in newer wood stoves for comparisons, and I think that is still too high. A lot of heat goes up the flue. EPA stove tests are done in a lab environment and done specifically to pass EPA requirements. In those tests, they are using perfectly dried wood and heating to specific levels of output. To that effect, they rate all cat wood stoves at 72% and non-cat wood stoves as 63%. They are not rating likely average home wood burning efficiency though. The EPA figures that the average EPA stoves are about 50% more efficient than the pre-EPA ones, and that on average an EPA stove will burn 30% less wood for the same heat value (which is saying the same thing). So an average EPA wood stove would be the average of cat and non-cat stoves, or 67.5% efficient (in lab burning), so that pre-EPA stoves would be about 45% efficient on average. Its all funny math, but that is how it comes out. In the lab at least.
My own results have shown about 25%, which was more than enough to win me over.
No complaints here with efficiency; my free fuel c/s/s (excluding recreational exercise for the task) is infanatly more efficient on my pocketbook than purchased fuel from a pipe
One thing to add to your post is the ratings you see from the gov has all non-cat stoves at 63% and all cat stoves are at 72% , they listed them that way as that was what those stoves had to meet to pass the test. Many of the cat stoves the actual test results were around 82%. Many of the non-cat stoves actually test around 76% to 81%. Some non-cat stoves from Europe that add in some fancy air mixing schemes are getting in the upper 80's. These results are from certified labs. But they are lab conditions and most people dont operate their stoves perfectly. The new Vogelzang Ponderosa tested by omni labs is 81% and its a non-cat stove. I have been looking at that stove as the fire box is 18.5" by 26" with, alot ,6 burn tubes, which may explain the higher efficiency in a non-cat stove.
OldSpark , I think the 30% thing I read was implying that in the old days when people had just old box stoves no technology , that most times they were burning them in the smoke dragon mode of dampering them down so much they were fire hazards , creosote machines. This was how alot of people used them. But I am sure properly operated with seasoned wood they would be more like you said 50% efficient.
Then compare that with the fact todays stoves are designed to be some what idiot proof as you can not shut the air all the way down per gov regulations as there is always the secondary air coming in preset and not controllable so as you can not turn the stove into a creosote producing machine all that easy.
Huntindog, yea I think the 30% is for the real old style woodburners and the 50% is for the air tight woodburners prior to the EPA stoves.
Spot on, that's exactly how I run my stove as well.
I will be ordering a stovetop gauge tonight. I have an IR handheld and will check my stovetop tonight after I get it in overnight burn mode where the only flames are those around the burn tubes. That seems to be my goal for a long burn as long as the coals do not go out in the middle of the night. I am still learning this stove.
I am temped to put a stovepipe damper for even more control. I have plenty of draft so the draft loss even when the damper is vertical would not give me problems lighting.
I guess that I am a control freak. LOL
I am also starting to focus on getting way ahead as far as cutting/splitting so that my wood is drier. I am calling a guy tonight that had his land logged off and he now wants the branches hauled out. Maybe I can get the name of the logging company and start finding locations even closer to me. This one is about 20 miles away. Not too bad. My F150 gets 18.4 miles to a gallon, probably 15 with the utility trailer and bed loaded.
I am already clearing the brush from an area on my land for the new wood. Hopefully about 6 full cords, about 2-3 years worth.
Thanks for all the great information on efficiencies. My Quadra Fire 5700 claims 77%. It is a 3 cubic foot box so it is a little low in the non-cat efficiency range that huntingdog1 gave above. In the brochure I have, none of the Quadra Fire stoves go over 80% (79 and change).
I use both the flue for startup and the stove top to maintain a good temp. They work well together and it is a good idea to know both the flu and the stove top. If you don't you could over heat the flue or over fire the stove and not know till it is too late.