Woodstove Efficiency Debate

[Firemoore98]

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.

Make no doubt about it an EPA stove requires fiddling.

Stove/wood furnace manufacturers design features that are intended to make the burn cycles easier, but I've never seen a 100% load it and forget it EPA stove. If you want something you load up, set the air/damper according to the stove temp you want, and want fine ash coals at the end, then you do NOT want an EPA stove.

The efficiency of getting every last btu out of a log comes at a cost of fiddling and heat cycles, if you don't embrace that concept you and your EPA stove won't get along.

Jason


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[Marshy]

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
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Nicely said.
To your point, here is a well written technical article about wood burners efficiency (from an emissions point of view) and what happens through the combustion cycle. I plan to read that later, lost of good info in it.
http://www.mha-net.org/html/p-tieg02.htm

 

[Chris-PA]

at this stage need you to shut down the "secondary air valves"

Actually it's the primary air that gets shut - with most of these stove you can't stop down the secondary air (that comes in from the air manifold over the fire)

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.

How you load the wood makes a huge difference with how these stoves run. If you load the firebox full of straight splits that sit tight together and prevent air from flowing from the bottom up through the wood load then you will much more easily end up with unburned logs buried in ash.

Sounds like a guy needs to be retired with nothing to do before he buys an EPA stove.

It's really not that hard.

 

[Del_]

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.

Getting a complete burn here.

Nothing but pure ash comes out of our stove.

 

[milkman]

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.

Oh yes, there are some, I have one with grates from the '90s and if it gets replaced, it will be with a Jotul 500 which also has a grate.

 

[Marshy]

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.

IDK, I don't fiddle that much with my stove. Rake coals forward each time I load it. If the stove thermometer tells me its in the active range (for the cat) then I close the bypass door. Instruction by the manual say leave it on HIGH for 20 mins after reloading before turning the thermostat down. I leave mine on HIGH and just load the stove to the heat needed. Most of the time its rake the coals, load it, close the bypass and walk away.

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.

Jotul does. My BK stove states in the manual to not use a grate in the stove. I believe it says it could cause overfiring of the stove.

Actually it's the primary air that gets shut - with most of these stove you can't stop down the secondary air (that comes in from the air manifold over the fire)
How you load the wood makes a huge difference with how these stoves run. If you load the firebox full of straight splits that sit tight together and prevent air from flowing from the bottom up through the wood load then you will much more easily end up with unburned logs buried in ash.
It's really not that hard.

In most all of these stoves combustion air doesn't flow up through the coals. Air is brought in through tubes in the walls or top of the firebox and wash over the door glass for primary air. The stoves that use secondary air have air tubes that mix the air in the secondary combustion area of the firebox. I believe the reason they don't have that kind of flow anymore is because it causes increased particulate in the flue gas (only a guess though).

 

[Marshy]

Oh yes, there are some, I have one with grates from the '90s and if it gets replaced, it will be with a Jotul 500 which also has a grate.

Got any pics? I would like to see inside one.

@Del_ , is that what you have?

 

[Chris-PA]

In most all of these stoves combustion air doesn't flow up through the coals. Air is brought in through tubes in the walls or top of the firebox and wash over the door glass for primary air. The stoves that use secondary air have air tubes that mix the air in the secondary combustion area of the firebox. I believe the reason they don't have that kind of flow anymore is because it causes increased particulate in the flue gas (only a guess though).

Just as with both of mine. However, the primary air flows down across the window and then into the front of the bottom row of logs. Unless you block that flow off by the way you stack the wood or by stopping it down too hard. If you keep enough primary flow the coals burn hot underneath and cook off the wood around them. The smoke from this rises up to the top of the firebox and hits the heated air from the secondary air manifold and combusts.

If it can't flow through then there isn't enough heat from below and the thing won't work.

Also, you can stack the wood so high that the air jets from the secondary air manifold blast directly into the wood - depending on the wood and conditions sometimes this will cause ash to bury and smother the fire at the bottom.

 

[milkman]

Got any pics? I would like to see inside one.

@Del_ , is that what you have?

I have a Consolidated Dutchwest 2462 that has a catalyst and grates, the Jotul f500 Oslo has grates and is EPS stove, Jotul f600 also. I like the 500 because it has a side door on the left, the 600 side door is on the right. Just google Jotul F500 Oslo and find pages of pictures some showing the grate.

 

[Firemoore98]

Great explanation Chris. More is not better with EPA stoves. Overloading them interrupts the operation/perceived efficiency.


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[hanniedog]

Mt Harman wood boiler is 100 % efficient. What ever wood you put in it gets burned up 100%

 

[Marshy]

Mt Harman wood boiler is 100 % efficient. What ever wood you put in it gets burned up 100%

To say its 100% efficient is not accurate just because all the wood you put into it burns completely. There are heat losses up the flue that make it less than 100% efficient. 100% efficient would mean that 100% of the heat generated by the combustion goes into the water jacket for heating the hydronic system. It also meant that 100% of the available BTU's in the fuel are converted to heat during combustion, which is unlikely.

Just as with both of mine. However, the primary air flows down across the window and then into the front of the bottom row of logs. Unless you block that flow off by the way you stack the wood or by stopping it down too hard. If you keep enough primary flow the coals burn hot underneath and cook off the wood around them. The smoke from this rises up to the top of the firebox and hits the heated air from the secondary air manifold and combusts.

If it can't flow through then there isn't enough heat from below and the thing won't work.

Also, you can stack the wood so high that the air jets from the secondary air manifold blast directly into the wood - depending on the wood and conditions sometimes this will cause ash to bury and smother the fire at the bottom.
View attachment 546801

I see what you mean now. Disregard, I thought you were saying something else like air enters into the firebox through a grate that's under the fire/colas like my old Shenandoah.

 

[GVS]

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.

The EPA units will "melt" down all the wood to ashes,it just amounts to how long you're willing to wait for it to happen.Give the fire more air and it happens faster.

 

[CaseyForrest]

No it doesn't "choke the fire down"
*

I'll stand corrected then.

sent from a field

 

[CaseyForrest]

Our hearthstone stove burns most efficiently when the top stones are around 500 degrees. The secondaries kick off right around 475 and when they start burning, I turn the main air almost completely off. Normally no visual flames from the wood burning, but from the gases burning.

The stove maintains its heat from the secondaries.

sent from a field

 

[CaseyForrest]

I would like to add to the process stated earlier about how to best run a high efficiency stove.

I've found there is a sweet spot in reloading the stove. I'll normally wait till the last bits of wood coal up but most of the time the wood that is still in log form can be broken up and spread out. By doing this the firebox stays relatively hot and getting the secondaries to fire back up is easier. Sometimes it requires no air adjustment but most of the time I have to give it just enough air to get them going and then shut it back down.

sent from a field

 

[CaseyForrest]

There is also a sweet spot in putting enough wood in the firebox. Not enough wood and there isn't enough mass to produce heat to get the secondaries going.

sent from a field

 

[Chris-PA]

I would like to add to the process stated earlier about how to best run a high efficiency stove.

I've found there is a sweet spot in reloading the stove. I'll normally wait till the last bits of wood coal up but most of the time the wood that is still in log form can be broken up and spread out. By doing this the firebox stays relatively hot and getting the secondaries to fire back up is easier. Sometimes it requires no air adjustment but most of the time I have to give it just enough air to get them going and then shut it back down.

sent from a field

It also depends on what you put in. Sometimes I'll throw in one or two small splits on top and the secondary combustion will kick off again, extending the secondary burn while the rest of the load burns down. Light wood like tulip or even the ash I usually burn works well. Recently I had some sassafras which worked great for that - the oils in that burn crazy on the secondaries.

 

[stevetheboatguy]

I'm probably in a minority. But the efficiency of my stove or someone else's doesn't bother me too much.
I made a mid sized owb a few years ago. And I heat my house (about 2000sq ft old and poorly insulated) three car garage (also poorly insulated) and a 20x30 shed. All from one heat source. I use less than feeding three different stoves. I can set the thermostats to where I want them independently and I don't have to mess around with anything.
I fill it when I wake up, check it mid day (usually fine unless it's sub zero or 40mph wind) and fill it again when I go to sleep.
Sometimes I get excessive coals, but that's ok. I rake them forward and let the stove run open for a hour and they are usually reduced to ashes. I shovel it out about every two weeks and get about a five gallon bucket full.
I burn about 10-12 cord a year and it doesn't bother me. I know I could get by with around eight cord with a newer gasification unit, but I would have to be more careful of what I burn.
Right now today it is windy as heck and I have a couple of half rotted stumps loaded to burn. I couldn't do that with a newer gasification stove.

So call me inefficient and happily warm.

Steven

 

[CaseyForrest]

It also depends on what you put in. Sometimes I'll throw in one or two small splits on top and the secondary combustion will kick off again, extending the secondary burn while the rest of the load burns down. Light wood like tulip or even the ash I usually burn works well. Recently I had some sassafras which worked great for that - the oils in that burn crazy on the secondaries.

I agree. I can get secondary combustion going alot faster with basswood than with oak or locust. Im sure some of that has to do with the shear mass of the wood and getting it all up to temp.

Of course, the times when I come home and current inhabitants forget to load the stove and I try to get a load of locust going on a small bed of coals requires full air to get the firebox hot again, like I'm trying to do right now. I could get it going faster with smaller splits, but I try to save those for fill in during overnight burns.