I've learned that the wood stove heating efficiency listed by the EPA is a default value selected by stove type (cat or non-cat). I would like to compare actual efficiencies for various stoves. Is there such a list? Could forum viewers post efficiencys of high performance stoves they know of?
Wood Stove Efficiency
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Check out grams/hour of smoke given. If the stove doesn't produce smoke it is using it's fuel quite effectively.
Matt
Matt
Efficiencies can vary so much due to chimney setups, weather, wood and other factors. Most Manufactures have their own cordwood tests for efficiencies and the highest I've seen is Blaze King at 82%. And I also found out the other day from Woodstock that their stoves run 80% cordwood test. Don't know if I really believe a woodstove can be over 70% tho, you need some heat to create draft.
Another thing to consider is ease of operation. As Todd stated, some of that heat is needed to create draft. If the stove was too efficient it may make it touch and go on getting it started and keeping it going at max efficiency.
The down draft stoves are an example of this like the VC Dutch West Non Cat and my Lopi Leyden. These are good and efficient stoves but they are not the easiest stoves to operate.
The down draft stoves are an example of this like the VC Dutch West Non Cat and my Lopi Leyden. These are good and efficient stoves but they are not the easiest stoves to operate.
Hello Mission Creek,
There are many fine stoves out there. Efficiency is an excellent metric to follow,
as general stove quality will usually be a part of the design package.
Look at all of your local dealers, just to talk stoves and get a feel of the wood burner
you want to be. Even if you want to install it yourself.
Search the web for all of the top brands Jotul, Woodstock, Hearthstone, etc. for efficiency info and
specifications. Heck, I love my Vermont Castings Encore NC! But, make up your own mind.
Research all that you can before the actual order is placed.
There is lots of info also here on Hearth.com. Use it in your decision making.
There are many fine stoves out there. Efficiency is an excellent metric to follow,
as general stove quality will usually be a part of the design package.
Look at all of your local dealers, just to talk stoves and get a feel of the wood burner
you want to be. Even if you want to install it yourself.
Search the web for all of the top brands Jotul, Woodstock, Hearthstone, etc. for efficiency info and
specifications. Heck, I love my Vermont Castings Encore NC! But, make up your own mind.
Research all that you can before the actual order is placed.
There is lots of info also here on Hearth.com. Use it in your decision making.
As others have said, I am of the opinion that the final efficiency you get has more to do your install details, your skill as an operator and the MC of your wood than the design of your stove (provided its a modern, EPA-rated unit). So, get a quality stove, a good chimney, dry wood, and learn how to drive it for efficiency. In the end, you'll know you're burning more efficiently than 90% of woodburners.
Of course, if you care about REAL efficiency---its not too hard to estimate.
'Geek out' warning.....
IF you have another heater (with a rated BTU output), and you can hear it cycling on and off, you can mark down the times while you're hanging out, and estimate its duty cycle at a given outdoor temp. IF you do this for a few outside temps, you will likely get a pretty reliable measure of your heating demand, which should be pretty much proportional to the difference in inside/outside temps. Note: I do this at night and cloudy days so I don't get contributions from solar input.
Now, you weigh a 50-100 # load of wood, fire up your stove, burn the wood as you normally do, and time how hours elapse from the last time your furnace turned over until the first time it does after the fire goes out. You then compute how much demand you displaced, and compare it to how many BTUs were in the load (here you need to estimate the MC as well as the weight).
Now, of course, this method is not perfect if your heat distribution is poor. Imagine your stove is close to the tstat, and you just heat one room and the tstat for 12 hours while the house freezes. After burnout, your furnace comes back on and has a lot of catching up to do heating the freezing house. Still, if your house is staying pretty even while you do your expt, the result should be ok. Any heat stored in your stove/hearth gives an error in the other direction. For a long burn cycle these errors both get smaller.
Even if the eff number is inaccurate, you are still counting how much fossil fuel and $$ you are saving per actual load of your actual wood.
BTW, I've done this a couple times, and I come up with 50-55% efficiency from my POS stove burning <20%MC wood.
Of course, if you care about REAL efficiency---its not too hard to estimate.
'Geek out' warning.....
IF you have another heater (with a rated BTU output), and you can hear it cycling on and off, you can mark down the times while you're hanging out, and estimate its duty cycle at a given outdoor temp. IF you do this for a few outside temps, you will likely get a pretty reliable measure of your heating demand, which should be pretty much proportional to the difference in inside/outside temps. Note: I do this at night and cloudy days so I don't get contributions from solar input.
Now, you weigh a 50-100 # load of wood, fire up your stove, burn the wood as you normally do, and time how hours elapse from the last time your furnace turned over until the first time it does after the fire goes out. You then compute how much demand you displaced, and compare it to how many BTUs were in the load (here you need to estimate the MC as well as the weight).
Now, of course, this method is not perfect if your heat distribution is poor. Imagine your stove is close to the tstat, and you just heat one room and the tstat for 12 hours while the house freezes. After burnout, your furnace comes back on and has a lot of catching up to do heating the freezing house. Still, if your house is staying pretty even while you do your expt, the result should be ok. Any heat stored in your stove/hearth gives an error in the other direction. For a long burn cycle these errors both get smaller.
Even if the eff number is inaccurate, you are still counting how much fossil fuel and $$ you are saving per actual load of your actual wood.
BTW, I've done this a couple times, and I come up with 50-55% efficiency from my POS stove burning <20%MC wood.
To continue in the geeky vein, different chimneys are going to need different inlet flue-gas temperatures in order to create the same draft... and also in order to maintain non-condensing (= non-creosote-forming) conditions through their whole length. On top of that, different chimneys are going to return different amounts of heat back into the living space... a freestanding stove venting straight up through twelve feet of exposed pipe is a much different proposition from the same stove venting straight into an exterior brick chimney.
So, a big part of the actual installed efficiency of a stove depends on the chimney... how much of the stove's heat output does it need to operate, and how much of the stove's output does it return to the room. The chimney is both the power source for the stove draft, and (usually) part of the heat exchange surface of the overall system.
I would guess that the stoves themselves are pretty similar in terms of converting wood into heat... they all burn pretty clean these days. If the fire's not making smoke then it is likely turning nearly all of the wood into heat. The big question I think is how much of that heat is getting sent up the stack.
I agree it would be nice if we got more numbers to describe these stoves... efficiency under some kind of standard conditions, required draft for various BTU burn rates, heat output for various BTU burn rates vs exhaust temperature, stuff like that. Then we'd have more info to go by in terms of matching stoves to installations.
Eddy
So, a big part of the actual installed efficiency of a stove depends on the chimney... how much of the stove's heat output does it need to operate, and how much of the stove's output does it return to the room. The chimney is both the power source for the stove draft, and (usually) part of the heat exchange surface of the overall system.
I would guess that the stoves themselves are pretty similar in terms of converting wood into heat... they all burn pretty clean these days. If the fire's not making smoke then it is likely turning nearly all of the wood into heat. The big question I think is how much of that heat is getting sent up the stack.
I agree it would be nice if we got more numbers to describe these stoves... efficiency under some kind of standard conditions, required draft for various BTU burn rates, heat output for various BTU burn rates vs exhaust temperature, stuff like that. Then we'd have more info to go by in terms of matching stoves to installations.
Eddy
Its interesting to consider other factors related to stove efficiency. However I still need help locating the base efficiency numbers for the stoves themselves. I was already familiar with the outstanding blaze king 82.5% efficiency. Are there any other stoves that perform that well?
And don't blindly believe the dealer. When I was shopping around, one dealer said a particular small Regancy model was in the 80-85% efficiency range. Although, the tag on the stove said 70-75% if I recall correctly...
They will tell you what want to hear to make a sale. You are doing it right by trying to get informed ahead of time.
They will tell you what want to hear to make a sale. You are doing it right by trying to get informed ahead of time.
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