Woodstove Efficiency Debate

[Marshy]

Calling @Whitespider!

Spidy's been asking for it so let's make it happen. Put your big boy pants on everyone and don't forget your knee high boots, this thread will likely get deep. There'll be some math involved and some bickering Im sure but lets keep it civil. For the folks who like a good debate it should be entertaining if your interested in efficiencies of stoves. Spidy's a keyboard wizard when it comes to long replies so don't get scare, this will likely get long winded.

Spidy, do you want to start? Please lay out your argument. Give us all the necessary inputs to compare two stoves; efficiencies, assumed cycle time (12 hr?), Amount of wood (lbs and/or BTU/lb), and any other assumptions needed. Try to stick to facts, look up the specs of your wood stove!
I'll be back to check.

Keep in mind as we go on the journey, I don't believe its fair to compare your forced air combustor to a free standing stove like the BK King, they operate totally different. Your stove can provide heat on demand by turning on a combustor fan then choke down when not on, while a BK stove is a constant demand stove. That is the primary reason your can get a longer burn cycle with a lower efficiency as compared to a stove like a BK or other traditional stove.

Lets start with a problem statement! I recall you saying;
"You flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated"

The floor is yours Spidy.

 

[Del_]

 

[Firemoore98]

Smoke is fuel; if it's black it has petroleum in it, if the flames are orange it has Carbon Monoxide in it amongst many other highly flamble yet unburied gasses.

As background I am a firefighter, have a bachelors degree in physics, I build custom BBQ smokers and run a BBQ catering business and I have 2 wood burners I use to heat my house and my detached barn (and justify all my chainsaw equipment to the wifey). I have a high effiency quadra fire 2100i insert that re burns the flammable gases that would have other wise escaped out the flu. And I have a lower efficiency wood stove setup in my garage. Both units have their merits, the high efficiency insert burns very clean and does go through a bit less wood than a comparable wood stove that was not "high efficient" and allowed the flammable products of combustion to escape into the atmosphere instead of re burning them and turning that dark smoke and CO into heat energy by re burning it. The downside is it requires very dry seasoned wood and it has heating cycles, you cannot load too often or you disturb the pyrolysis cycles and excess ash/charcoal will accumulate. In other words you have to be patient and allow the high efficiency stove to get hot enough to burn off the flu gas fuel, which takes time and you cannot re load wood too early, the stove will cool back down a bit. This is a really nice unit for the family room in terms of ambiance, the flames are beautiful colors like the picture above. It also keep me moving in the winter and I like having something to tend to when I'm on the the couch, it's like a hill billy fit bit, ideally I need to reload it every 3ish hours, but hey I'm watching tv so moving around is good for me, but the high efficiency means I'm lugging less wood into the house too.

The wood stove I have in the garage is like an f150, she just chugs along, easy to warm up, maintains temps with most any fuel, re load whenever you want, isn't nearly as picky about firewood moisture content or size of splits and she doesn't have cycle stages of building coals and enough heat to re burn flu gases like the high efficiency unit, so I get a more even consistent heat. The cons of this unit is I do notice an increase in wood consumption proportional to heat output. For me this is not a concern, my property produces more firewood annually than I could possibly burn. I like this unit in the garage because I can work on projects and load it when I get a chance, I do not have to pay attention to heating cycles.

I'm not sure it's fair to say one is better than another. The high efficiency units do produce more heat per piece of firewood yes I agree with that, but it's at a cost of "finickynes", as stated about high efficiency is all about perfect pyrolysis therefore dry seasoned smaller splits are a must, and the operator must understand the process to operate such a stove and how to read the cycles of combustion that are occurring. A good operator with god seasoned wood can operate a high efficiency stove like a musical instrument and get close to even long term consistent heat from the unit, but it's nonetheless a process.

I'm not sure I'm answering any questions or even making any sense to anyone, but myself. I was just trying to explain that high efficiency stoves have their places, but they also have downsides. I notice that stove people (not unlike truck people or chainsaw gurus) often think what they have is the best, they will boast about the pros and skip over the cons. I have one of each type of stove and I understand the function of each unit and utilize each in an application where I feel the pros out weigh the cons.

Jason


Sent from my iPhone using Tapatalk

 

[Whitespider]

Spidy's been asking for it...

Asking for a wood stove efficiency debate??
Well I'll participate, but first define "efficiency".
Are we talking combustion efficiency, or heating efficiency, or operation efficiency??
Are we talking about squeezing every last available BTU from the fuel, or about how fast we can raise the temperature of my entire home by 5°, or about how much user input is required to maintain a given temperature of my entire home??

I don't believe its fair to compare your forced air combustor to a free standing stove like the BK King...

I agree... to a point... but my current appliance is the only "forced air combustor" I've ever had... all the "forced air" really does is give me a bit more margin of error when loading.

And... I really don't know what more there is to debate after Firemoore98's post... he pretty much hit all the points to be made.
Good post Jason.
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[CaseyForrest]

, I don't believe its fair to compare your forced air combustor to a free standing stove like the BK King, they operate totally different.

If the only standard is the wood burning, there is no argument. But when you start getting into high efficiency stoves that start to reburn particulates, there is an argument that you can get more heat and longer burns from the same amount of wood.

Increasing HP in gasoline engines is the best analogy I can come up with in regards to increasing the efficiency in burning "something" A gallon of gas has the same energy potential as another gallon of gas. But put each gallon into different era engines of the same displacement....

 

[midwest_170]

I have a old earth stove (approx 5 cuft) and my house is 1900 sq ft on the main level. I have a full finished walkout basement which is where the stove sits. The house is mid 90s construction so insulation is pretty decent. My chimney is a 8" square tile but surrounded by a very large/thick layer of limestone rock. The chimney runs up through the middle of the house. The stove will produce 8 to 12 hours of heat depending on wood type being burned. At 1st I had trouble getting heat out out that stove then I built a grate to introduce air under the fire and it was a totally different game. I have to really choke down my stove to keep it from melting down. We had a 48hr stretch of sub zero highs this year and I had no problem keeping the house in the 70s.

Added

The wood I'm burning has been sitting in a stack at least 3 years. The only smoke I get out the stack is the few minutes after I reload the stove and it's getting back up to temp. Once it's burning hot my stack is burning clean.

 

[CaseyForrest]

I agree... to a point... but my current appliance is the only "forced air combustor" I've ever had... all the "forced air" really does is give me a bit more margin of error when loading.


*

No... Not even close. Your wood furnace, likely, chokes the fire down when heat isn't called for. And then opens a damper/kicks on a fan when heat is called for.

There is no point, they are not even in the same ballpark.

 

[milkman]

What's to debate, I put wood in and get heat out.

 

[Firemoore98]

What's to debate, I put wood in and get heat out.

Wood stove guys debate the merits and features of wood stoves just like chainsaw guys debate why they have a favorite between the 550xp and ms261cm.

My wood stove habit fuels my chainsaw addiction, my chainsaw addiction gets a little out of hand and I tell the wife we need to burn more wood, gets really cold out and I tell the wife my back hurts and I need that new mid size saw I've been talking about...

Jason


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[Marshy]

Thank you for weigh in @Firemoore98. You bring up valid points to operating both types of stoves.

@Whitespider, I was hoping you would want to carry on where you left off in the chimney draft thread. Should I quote your from that thread?

 

[Marshy]

Asking for a wood stove efficiency debate??
Well I'll participate, but first define "efficiency".
Are we talking combustion efficiency, or heating efficiency, or operation efficiency??
Are we talking about squeezing every last available BTU from the fuel, or about how fast we can raise the temperature of my entire home by 5°, or about how much user input is required to maintain a given temperature of my entire home??


I agree... to a point... but my current appliance is the only "forced air combustor" I've ever had... all the "forced air" really does is give me a bit more margin of error when loading.

And... I really don't know what more there is to debate after Firemoore98's post... he pretty much hit all the points to be made.
Good post Jason.
*

Im letting you decide what the debate is. Your argument was "You flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated"
Should I work around that?
What model is your DAKA?

 

[Whitespider]

No... Not even close. Your wood furnace, likely, chokes the fire down when heat isn't called for.

No it doesn't "choke the fire down" Casey.

When the draft blower ain't running, the furnace burns at a predetermined rate (set by my flue damper) no different than any other firebox... it's still making heat, and the circulation blower is still running, or cycling (controlled by the temperature of the air jacket surrounding the firebox). There is no damper that opens and closes. I'm still loading the firebox according to expected heat demand. But if I load it a bit on the light side and the house temperature falls, the thermostat will start the draft blower to increase the burning rate a bit. If I load it a bit too heavy, the draft blower never comes on and the house will overheat. That's what I mean by the draft blower gives me bit more margin of error when loading... I try to load it so the thermostat kicks on the draft bower every 1½-2 hours for a couple of minutes, that way the house don't overheat, it stays a constant 70°.

It actually runs the most efficiently when the draft blower ain't on and the box is running at my predetermined rate... the "sweet spot" so to say. The draft blower increases combustion rate, which makes more heat (for a given fuel load), but also increases fuel usage (reduces combustion efficiency). I set the "limit" on my furnace down from 200° to 180° so when the draft blower does come on it it cycles off when the air jacket reaches that temperature... and only comes back on when it falls to about 140°. That way the draft blower ain't causing the furnace to use as much fuel but still pumps out a ton of heat when in demand. I also changed the on/off setting for the circulation blower from 130°/90° to 155°/120° so the firebox runs a bit hotter in the predetermined rate... yet will run continuously when the thermostat is asking the draft blower to run.

I also installed a large 3 speed circulation blower... it defaults to low speed, but when the thermostat calls for heat it bumps up to medium speed, and if the thermostat is calling for heat and the downstream duct temperature goes over 100° it bumps to high speed. This also reduces the amount of time the draft blower is required to run... which, as stated, increases fuel consumption.

90% of the time the draft blower ain't running, the circulation blower is cycling at low speed, and the size of the fuel load (that I choose based on expected demand) is what controls the heat output of the box... the draft blower just gives me a bit more margin of error to load a touch on the light side so the house never overheats.
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[midwest_170]

How many of you guys burning the EPA stoves get a complete burn of all fuel? I have a friend that has one of these stoves and he's always throwing coals out to make more room for wood. The only thing that gets thrown out of my stove is pure ash.

 

[Chris-PA]

Part of the problem with such discussions is that "efficiency" is a ratio of two things, which usually no one bothers to define, and it gets confused with output rate and total wood use, and different types of wood burning devices with different capacities get compared. Then the whole conversation becomes gibberish that turns your brain to mush.

The downside is it requires very dry seasoned wood and it has heating cycles, you cannot load too often or you disturb the pyrolysis cycles and excess ash/charcoal will accumulate. In other words you have to be patient and allow the high efficiency stove to get hot enough to burn off the flu gas fuel, which takes time and you cannot re load wood too early, the stove will cool back down a bit.

Some years ago we got a second, smaller secondary combustion stove put in upstairs (sorta by accident). It's turn out to be a great setup, as I can run just the smaller stove in moderate temps, both if its really cold, or I can stagger load the two in order to let the cycle finish without building up coals. Plus I can use wood of varying lengths, as the stoves are different sizes.

 

[Chris-PA]

How many of you guys burning the EPA stoves get a complete burn of all fuel? I have a friend that has one of these stoves and he's always throwing coals out to make more room for wood. The only thing that gets thrown out of my stove is pure ash.

I do. I never throw anything away but ash and few small coals.

 

[Whitespider]

Im letting you decide what the debate is. Your argument was "You flat cannot burn less fuel, over a longer time period, and get the same per-hour rate of heat generated"
Should I work around that?
What model is your DAKA?

I made that argument with the math twice in the other thread... but that had nothing to do with efficiency, it was about the hourly rate of heat output accomplished via a faster burn rate. Your stove, according the the specs, will run 12 hours on the "high" setting... that's it, that's the fastest rate it will burn at... I could, if I wanted to, make my box burn the same amount of fuel in 2-3 hours, and the heat coming off it would melt the buttons on your shirt from 10 feet away.

The DAKA is a modified 622FBT.

How many of you guys burning the EPA stoves get a complete burn of all fuel? I have a friend that has one of these stoves and he's always throwing coals out to make more room for wood.

I've got an EPA stove in the garage/shop... it needs constant fiddling with, which is a huge pain in the azz... and I toss out a lot of coals and charcoal.
My "smoke dragon" makes fine ash... and all I do is open the door, toss in the wood, and slam the door shut.
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[Firemoore98]

How many of you guys burning the EPA stoves get a complete burn of all fuel? I have a friend that has one of these stoves and he's always throwing coals out to make more room for wood. The only thing that gets thrown out of my stove is pure ash.

Yep, been there done that.... have your buddy check his firewood with a moisture meter. You really want 14% for most EPA stoves. If your above that the stove has to work to hard to pre heat the fuel and the efficiency is lost and pyrolysis peak performance is not achieved. The moisture cools the glue in terms of steam as well.

Secondly as I mentioned in my first post the EPA stove works in cycles. 1st you get a bed of coals going with small dry kindling 2nd you add a moderate amount of wood (not too much or your coals won't be able to creat pyrolysis) 3rd be patient usually about 15 minutes or so of those flames working on your dry firewood will create a scenario where the wood is off gasing sufficiently and then you can close the door and most EPA stoves at this stage need you to shut down the "secondary air valves". 4th be patient, let this burn down to coals, DO NOT RELOAD TOO EARLY.

A lot of people especially on really cold days are trying to keep the heat as high as possible at all time and re load way too often. Chris above mentioned having 2 stoves and being a master of his setup alters his cycle so at all time 1 of his 2 stoves is giving off its maximum heat. If your house cools down a bunch at this step in the cycle your house is poorly insulated and or your stove is poorly sized for the outdoor climate/size of your house.

Step 5... start back at step one. There will be a range of heat output throughout this process and you just need to allow each step to occur. This is the down side to EPA setups...

Have your buddy review these steps and I bet you a shiny nickel his ash will be cut dramatically down.

Jason


Sent from my iPhone using Tapatalk

 

[Marshy]

How many of you guys burning the EPA stoves get a complete burn of all fuel? I have a friend that has one of these stoves and he's always throwing coals out to make more room for wood. The only thing that gets thrown out of my stove is pure ash.

Sounds like his stove is undersized. He's trying to keep his stove operating closer to its peak output buy maintaining a high load of fuel in the firebox but he's not allowing the stove to complete its burn cycle and digest the coals. If the stove is properly sized to the demand then the stove can be allowed to burn longer and burn down those coals while meeting the heating demand.
My BK build coals in the back of the firebox but burns them down to complete ash at the front by the loading door. I push the ash under the coals to the back and take the coals forward ever time I load the stove. If it really cold out and I'm trying to keep my stove operating closer to it's peak output then coals can start to build up. I take them forward any only put one split on top right at the door to promote air flow to the coals and ensure I'm getting enough heat while they get a chance to bring down. On warmer days I dont add the split on them and just let then do their thing.
I clean the firebox of ash once a week. I take the coals to the sides and push the ash down the cleanout plug hole. Some coals are thrown away but they are the size of nickels, at best quarters. I'm not sifting coals from ash to save them and I'm not letting the stove go completely cold to clean the ash.

 

[midwest_170]

Yep, been there done that.... have your buddy check his firewood with a moisture meter. You really want 14% for most EPA stoves. If your above that the stove has to work to hard to pre heat the fuel and the efficiency is lost and pyrolysis peak performance is not achieved. The moisture cools the glue in terms of steam as well.

Secondly as I mentioned in my first post the EPA stove works in cycles. 1st you get a bed of coals going with small dry kindling 2nd you add a moderate amount of wood (not too much or your coals won't be able to creat pyrolysis) 3rd be patient usually about 15 minutes or so of those flames working on your dry firewood will create a scenario where the wood is off gasing sufficiently and then you can close the door and most EPA stoves at this stage need you to shut down the "secondary air valves". 4th be patient, let this burn down to coals, DO NOT RELOAD TOO EARLY.

A lot of people especially on really cold days are trying to keep the heat as high as possible at all time and re load way too often. Chris above mentioned having 2 stoves and being a master of his setup alters his cycle so at all time 1 of his 2 stoves is giving off its maximum heat. If your house cools down a bunch at this step in the cycle your house is poorly insulated and or your stove is poorly sized for the outdoor climate/size of your house.

Step 5... start back at step one. There will be a range of heat output throughout this process and you just need to allow each step to occur. This is the down side to EPA setups...

Have your buddy review these steps and I bet you a shiny nickel his ash will be cut dramatically down.

Jason


Sent from my iPhone using Tapatalk

That's the 1st thing I thought too was the wood so I gave him a truck load of locust that had been split and stacked about 4 years ago. Said it was a little better but not much. I know he doesn't take the time to fiddle with all those steps you mentioned above so that is probably the problem. Sounds like a guy needs to be retired with nothing to do before he buys an EPA stove.

 

[midwest_170]

Sounds like his stove is undersized. He's trying to keep his stove operating closer to its peak output buy maintaining a high load of fuel in the firebox but he's not allowing the stove to complete its burn cycle and digest the coals. If the stove is properly sized to the demand then the stove can be allowed to burn longer and burn down those coals while meeting the heating demand.
My BK build coals in the back of the firebox but burns them down to complete ash at the front by the loading door. I push the ash under the coals to the back and take the coals forward ever time I load the stove. If it really cold out and I'm trying to keep my stove operating closer to it's peak output then coals can start to build up. I take them forward any only put one split on top right at the door to promote air flow to the coals and ensure I'm getting enough heat while they get a chance to bring down. On warmer days I dont add the split on them and just let then do their thing.
I clean the firebox of ash once a week. I take the coals to the sides and push the ash down the cleanout plug hole. Some coals are thrown away but they are the size of nickels, at best quarters. I'm not sifting coals from ash to save them and I'm not letting the stove go completely cold to clean the ash.

I doubt it's possible to buy a EPA stove with a grate then? I just can't imagine burning wood without a ash grate.