# Stove efficiency calculation

#### nortcan

##### Feeling the Heat
Hi all, I would like to know how to calculate the efficiency of a wood stove and on what is based the efficiency of a wood stove ! Thanks

Hi all, I would like to know how to calculate the efficiency of a wood stove and on what is based the efficiency of a wood stove ! Thanks
Pass the popcorn for this open can of worms! The replies to this should prove interesting if not even down right entertaining. I can assure you that the GB BB has already given you a “warped” sense of the term efficiency compared to most here. They just wouldn’t understand you. LOL!

Pass the popcorn for this open can of worms! The replies to this should prove interesting if not even down right entertaining. I can assure you that the GB BB has already given you a “warped” sense of the term efficiency compared to most here. They just wouldn’t understand you. LOL!
Sorry but I can't understand your curious answer...Everybody want an efficient wood stove but how many really know and understand it? Is it so offendant to ask that question ? And what do you mean by : GB BB, has already given....show me please that answer, I don't really remember it . Thanks for your great kindness.

Never said it was offensive to ask the question. Never even implied it.

GB Base burner…did you use the base burner?

Efficiency is simply the amount of BTUs going in divided by the BTUs going out thru the chimney (in heat and incompletely burned compounds).

That is measured in testing with a specific load of wood (at some moisture content), burning at a certain setting and measuring the heat output and analyzing the flow out of the chimney.

This testing is rarely representative of real world burning, even if the testing uses cordwood.
Packing density in the stove, moisture content, surface area, burning speed, etc. all affect the actual efficiency.

But the testing does intend to allow comparing different stoves because of a standardized burning approach.

The utility of this is often debated, not the definition of efficiency (=usable output/input).

Hi all, I would like to know how to calculate the efficiency of a wood stove and on what is based the efficiency of a wood stove ! Thanks
Wood btus loaded divided by btus to the room. Easy to say. Really hard to measure. Any epa rated wood stove an efficient enough for me.

Hoytman
I’ll submit there are different kinds of efficiency…even among those in the industry. So defining what efficiency means is the first order of operations here, not some formula. People ask that question all the time here and to each one it means something different.

One person came here recently and said to them efficiency meant longer burn times. It is my observation most new people coming here believe it to mean longer burn times. Another person, it was a moderator here, said it had nothing to do with longer burn. It doesn’t matter who is wrong or right as that doesn’t change people’s perception of what efficiency means to them.

I think first we need to ask ourselves where does that perception come from. Personally, I feel most people’s perception comes straight out of the automotive industry where efficiency to them translates to fuel mileage. So why wouldn’t they think wood fuel in a modern wood stove would give any less “mileage”/burn time?

I personally feel the above is why the definition needs to be debated, because a clear answer is NOT so, pardon the pun, “cut and dry”.

To some, btu’s goin in means only so many btu’s can come out…which only a partial truth and is often killed by stove design…and a not so little thing called a stoves “heat transfer efficiency” throws a wrench into what would have been a simple calculation for a single stove. Change stoves and “heat transfer efficiency” suddenly becomes a real thing…a real obstacle to take into consideration.

So again, I’m going to grab my popcorn and sit back and watch. Like other words that have multiple meanings, the term “efficiency” also has more than one meaning.

Todd
The fact that people misunderstand what efficiency means does not imply the meaning of efficiency is under debate.

It is fine to have a misunderstanding, and this website is good for that as it can correct mistaken ideas.

Such as mistaking time driven on a tank for miles driven.

I'm not trying to be disagreeable, but the meaning of a concept as efficiency, i.e. a concept that is expressible in numbers, is not dependent on opinions.

Now let the corn pop ;-)

bholler
Never said it was offensive to ask the question. Never even implied it.

GB Base burner…did you use the base burner?
OOPS, sorry for my answer, now I see what you meant, now I burn a Hearthstone Soapstone 8024. No more BB since a few Yrs. A bag was around \$5.00 Can. when I began with anth. now it's over \$20.00/bag ... As you can see, my English can be improved...Salutations from Québec.

Hoytman
I know that many opinions exist about efficiency of wood stoves, complicated calculations seem to be made especially to give peace of mind for custommers and for stove makers, about like the same thing for the burn times in labs versus in real homes. For a 81% LHV efficiency , is the heat loss from the stove going to the stove pipe/out of the house is : 19% ? And for a 77% HHV efficiency : 77% stay in home and 23% go outside of the home % ???

I know that many opinions exist about efficiency of wood stoves, complicated calculations seem to be made especially to give peace of mind for custommers and for stove makers, about like the same thing for the burn times in labs versus in real homes. For a 81% LHV efficiency , is the heat loss from the stove going to the stove pipe/out of the house is : 19% ? And for a 77% HHV efficiency : 77% stay in home and 23% go outside of the home % ???
That is the basic meaning of it. But you also have to factor in unburnt potential fuel escaping the chimney as well

That is the basic meaning of it. But you also have to factor in unburnt potential fuel escaping the chimney as well
Thanks, just to see for myself if I was right or fool about the efficiency meaning : I called many wood stove dealers and asked them the same questions about wood stoves efficiency and none had the same answers and didn't really know how how it works , so I can't imagine if asking the same questions on efficiency to ordinary stove buyers or stoves owners what would be the answers ???

this is it:

Thanks, just to see for myself if I was right or fool about the efficiency meaning : I called many wood stove dealers and asked them the same questions about wood stoves efficiency and none had the same answers and didn't really know how how it works , so I can't imagine if asking the same questions on efficiency to ordinary stove buyers or stoves owners what would be the answers ???

Many dealers don't know anything about wood stoves in general so they definitely will have no idea about efficiency.

stoveliker
the most basic definition of efficiency is
what you get out divided by what you put in.

Since it’s given as percentage you need to have the same units in the numerator as the denominator.

Miles per gallon is not an efficiency by my basic definition. Neither would length of burn.

stoveliker
When someone buy a wood stove, it's generally to heat a place. In the mind of many peoples, if a stove is rated : 81% LHV of efficiency, it means 81% of the heat is send in the home and 19% to the chimney and out of the home. And a lot of stoves dealers have troubles to really understand and explain how efficiency it works except for the taxes credits...But when I read the temperature on the TOP of my stove with cats. engaged and see : 400* F and get : 300*% F on the STOVE PIPE thermometer, at 11 inches from the top of the stove I doubt of the stove efficiency , I did many times that comparaison with same wood, same house, same of all. So a lot of heat is losted outside, In a real house, not in a lab. having nice words, nice math formulas, complicated chemistry words and so on the visions differt a lot, I don't think that result is showing a good effiency at all. And because the 2 cats. are located very close to the stove's outlet, it's normal to lose so much heat, the heat exchange distance is very short. When looking inside a Woodstock PH , we can see a heavy cast iron heat exchanger with fins and the wide cat is not close to the stove vent outlet. Hum !

...300*% F on the STOVE PIPE thermometer, at 11 inches from the top of the stove...
How are you measuring the temperature at 11 inches from the top of the stove? That is, what is the nature of your "STOVE PIPE thermometer"?

With a magnetic thermometer on the stove pipe, placed at 11 inches from the top of the stove.

With a magnetic thermometer on the stove pipe, placed at 11 inches from the top of the stove.
What stove do you have? How are you running it?

What stove do you have? How are you running it?
Hearthstone Heritage 8024. Usually around 350/ 400 * F on the top of the stove.

With a magnetic thermometer on the stove pipe, placed at 11 inches from the top of the stove.
Okay. Just keep in mind, you are not measuring the flue gas temperature. You are measuring (approximating, actually) the temperature of the outer surface of the flue pipe.

Hearthstone Heritage 8024. Usually around 350/ 400 * F on the top of the stove.
Ok but how far open do you have the air?

Okay. Just keep in mind, you are not measuring the flue gas temperature. You are measuring (approximating, actually) the temperature of the outer surface of the flue pipe.
Same thing for the thermometer on the outer stove 's top , measuring the outer too. You know, a stove pipe is so thin that it may not makes a very big difference , but I can do the same test with a probe thermometer, I have one on my Hearthstone Tribute stove pipe..