Woodstove Efficiency Debate

[CaseyForrest]

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.

Ours has a grate and ash pan.

 

[CaseyForrest]

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.

We used to have a Resolute Acclaim circa early nineties. The wood sat on a grate and directly below it was an ash pan. That was not an EPA stove although it had its own version of secondary combustion. It would burn wood down to a fine ash, no coals, no chunks with no input from me.

Our Hearthstone, however, does not always burn down to a fine ash. It will if we run it 24/7, but fires down shoulder season wont burn completely. This has an upside and a downside.... The upside is charcoal for getting the next fire going. The downside is some of this unburnt wood invariably makes its way into the ash pan when raking the ashes out. Now I'm not talking about large pieces, 1/2" and smaller. So not alot goes to waste.

 

[Marshy]

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.
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I looked up the specs of your stove and it said 125k BTU/hr max and 62.5k BTU/hr min. It also said 10 hr full load run time. The manufacture says the firebox is 16"x23" but I called them and was told it's 16"x25"x20" or 4.63cuft. My BK stove is 4.32cuft and they assume it will hold 91lbs of wood, or 703,390 BTU.

I don't believe this is a sound way to determine the efficiency of your stove but it's the best back of the envelop method I could think of... I calculated your stoves efficiency by assuming the a full load was 703k BTU (like BK says their full load is) and a 10 hr cycle on low. Interestingly it works out to be 89% efficient! (Magic?)

If I use that efficiency to figure out what your stoves average BTU/hr output is in a 12 hr cycle guess what it is!!! Nearly the same as the BK! 52,168 BTU/hr vs BK has 51,582 BTU/hr.


Do I really think your stove is 89% efficient? No chance in hell. So you might ask how does it last 12 hrs then..? Well, we get back into the heat on demand and the fact that we are comparing apples to oranges and forced air combustor throttle down significanly.

Now, do you really think a full load in the BK lasts 12 hrs? I hope not. Not unless they are saying the coal bed has just embers. I can tell you that it doesn't have usable heat for 12 hrs. The heating demand in my house becomes greater than the stoves output after 8hrs when I burn on hi and the house temp is just starting to lower. The stove has a really good bed of coals still and goes back into the active zone after raking the coals forward. All I have to do is reload and shut the door.

It's all a guess as to how much unburnt fuel is left in the firebox when I reload at the 8th hour. It would be a poor assumption to assume 1/3 of the load remains unburnt because the stove doesn't burn at 51k btu/hr over the entire 12 hrs. You would have to know the burn profile of the stove to understand that. That profile would look something like the graph I posted in the chimney draft thread.

The heat released in the 8 hr cycle is cross hatched in brown. The leftover fuel is in the orange area. If we have a plot from the manufacture like this we would know what the max BTU/hr output of the stove is and how long it maintains that output. Using math we could also calculate the area under the curve to see how many BTUs we used in that period and how many are left. The EPS stoves get rigorously tested so I bet they have all the tools and info available to make a plot like this. Most consumers and dealer will not know how to use it though. The above average person could use it and know how much extra heating power they have over their demand.

 

[Chris-PA]

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.

That's why I love to have some tulip around. One split of that and it's instafire.

 

[Whitespider]

The manufacture says the firebox is 16"x23" but I called them and was told it's 16"x25"x20" or 4.63cuft.

Just for reference... I cut my firewood to 16 inches, I've never used anything close to the full capacity of the box.
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[CaseyForrest]

Just for reference... I cut my firewood to 16 inches, I've never used anything close to the full capacity of the box.
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Is that for consistency in storage or habit?

 

[Whitespider]

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.

I've stopped trying to burn the denser hardwoods (like oak and locust) in my EPA stove... I mostly burn the smallish "trimmings" from elm, cheery, and the like. The dense hardwoods don't perform any better, but build up an unmanageable amount of coals.

I doubt it's possible to buy a EPA stove with a grate then?

Not impossible... but the combustion air is not fed directly under the grate, it still comes in over the top (unless there's one I'm not aware of).
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[Marshy]

Just for reference... I cut my firewood to 16 inches, I've never used anything close to the full capacity of the box.
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How deep is the bead of coals? Aint no magic about it, you better be packing a mighty bed of coals to only use half the firebox and get 12 hrs of heat.

 

[Whitespider]

Is that for consistency in storage or habit?

Partly habit... but it's also for easy of handling/loading for the girls in the house when I'm not around.
And... 16 inches is the max my EPA stove in the garage/shop will handle (shrug)
I have cut to 18 and even 20 inches... but that was more for expediency more than anything else.
16 inches has always worked, it's relatively easy for the girls to handle, and it will fit both fire boxes I use... so... it-is-what-it-is.
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[CaseyForrest]

Not impossible... but the combustion air is not fed directly under the grate, it still comes in over the top (unless there's one I'm not aware of).
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Our Hearthstone feeds its air in through a small opening directly in the center of the opening for the main door. It does have an airwash over the glass, but that is not the main air supply.

 

[JRHAWK9]

Wait till Phase 2 of the EPA testing is enforced in 2020. This will make a lot of manufacturers put up or shut up. My Vapor Fire already meets this extremely strict spec. So many stoves/furnaces out there today are grossly over-rated, and the new EPA testing will sort through all the BS.

 

[Marshy]

None of the EPA stove feed air through a bottom coal grate. It causes too much of the ash to become airborne and kills the EPS particulate count.

 

[Firemoore98]

I am currently burning 99% ash in my EPA stove. I've burnt a little cherry and really liked it and could tell it burnt hotter than my staple ash wood. I have a large surplus/server all years worth of ash both cut, and standing dead on my property, so it will be a few years before this is all gone.

I too like 16-18" splits where my stove could take nearly a 20" log, having airflow around the wood front and back with north south loading seems logical and my wood is only 10 months seasoned, so I figure shorter splits dry quicker? Just moved to a new house @2 years ago and I'm finally caught up on chores where I will be 1-rs ahead on firewood form here on out.

This has been an educational thread and I appreciate all the input.

What is everyone's favorite EPA stove firewood? And why?

Thanks

Jason


Sent from my iPad using Tapatalk

 

[CaseyForrest]

Partly habit... but it's also for easy of handling/loading for the girls in the house when I'm not around.
And... 16 inches is the max my EPA stove in the garage/shop will handle (shrug)
I have cut to 18 and even 20 inches... but that was more for expediency more than anything else.
16 inches has always worked, it's relatively easy for the girls to handle, and it will fit both fire boxes I use... so... it-is-what-it-is.
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Our old stove was supposed to take 16" wood. And it would as the firebox was sized for it... But getting through either of the openings with more than 1 piece of wood in it was a struggle. I had to cut at 15" just to be able to fill up the firebox.

Ill be stoked to get into the wood Ive cut to utilize the full firebox on both burners but that wont be until next year, if not the year after at our current rate of burning.

 

[Whitespider]

How deep is the bead of coals? Aint no magic about it, you better be packing a mighty bed of coals to only use half the firebox and get 12 hrs of heat.

Why do you say that??
I will say, if I'm expecting bitter cold I will build a coal bed just ahead of it moving in... maybe 4 inches deep at the extreme.

None of the EPA stove feed air through a bottom coal grate. It causes too much of the ash to become airborne and kills the EPS particulate count.

Hmmmmm.... now that makes sense... or at least the best explanation I've heard.
But it's the air being fed under the coal bed, and flowing up through it, that keeps the coal bed screamin' friggin' hot.
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[Whitespider]

Our old stove was supposed to take 16" wood. And it would as the firebox was sized for it... But getting through either of the openings with more than 1 piece of wood in it was a struggle. I had to cut at 15" just to be able to fill up the firebox.

Actually I shouldn't have said 16 inches max... the spec says 17 inches, but as you say, that's a struggle.
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[CaseyForrest]

What is everyone's favorite EPA stove firewood? And why?

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Ill be honest... I really like the stuff most everyone else walks over. The faux hardwoods. Mainly because its easy to come by.... People darn near pay you to take it.

BUT.... We too have an abundance of ash so that usually gets the nod. Ill save the hard hardwoods for when the temps drop and I need a more consistent output from the stove rather than a slight up and down.

So far this season we burned 80% basswood and red maple with a little silver maple mixed in. The rest has been a small amount of cherry, some white oak and honey locust which was brought up specifically when the temps dropped into the single digits and we have both the stove and the insert going.

What I don't like about the hard hardwoods is they are a bit more finicky to get a sustaining secondary burn going. But once they do get established, they run like the energizer bunny. The load of locust I put in the stove a couple hours ago is still firing the secondaries.

 

[CaseyForrest]

None of the EPA stove feed air through a bottom coal grate. It causes too much of the ash to become airborne and kills the EPS particulate count.

Hmmmmm.... now that makes sense... or at least the best explanation I've heard.
But it's the air being fed under the coal bed, and flowing up through it, that keeps the coal bed screamin' friggin' hot.
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That does make sense..

The ash door on the bottom of the stove is a saving grace for getting a new load going after an overnighter... Or just jumpstarting a load.

 

[Whitespider]

Do I really think your stove is 89% efficient? No chance in hell.

You do realize it has a secondary combustion chamber... right?? (DAKA calls it a secondary heat chamber).
Air is not fed into it separately, but when the draft blower is forcing air into the box you can look through the hole where the rod comes out to open the bypass and there's a friggin' firestorm happening in the secondary chamber.
Do I believe my furnace is 89% efficient?? Just like you... no chance in hell.
But, the way I run it, I'd easily believe 60%... and 70% wouldn't be unbelievable under certain operating conditions.
I also ain't believing your stove is 88% efficient in the real world... I might believe 82-83% under best circumstances, but only under best.
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[Marshy]

I am currently burning 99% ash in my EPA stove. I've burnt a little cherry and really liked it and could tell it burnt hotter than my staple ash wood. I have a large surplus/server all years worth of ash both cut, and standing dead on my property, so it will be a few years before this is all gone.
...
What is everyone's favorite EPA stove firewood? And why?

I like burning ash, the coals don't linger and build up. It burns down to ash fairly quickly giving up its heat and if you mix it with cherry you can get the perfect burn rate on the coals. The issue I have with cherry is it sparks a lot when the coals get fresh air. A man could lose part of an eyebrow easily.
IDK why my favorite EPS stove it, its not like I have use 3-4 of them to be able to know any of their differences. I do know what I would like my EPA stove to be and that is, heat more like my non EPA stove! That thing 5 minutes next to that stove and your metal rivets in your jeans became branding buttons. You'd walk away feeling your skin sizzle on the inside of the fabric of your jeans. The problem is, the radiative heat off that stove is not safe for the house. I bet the floor joist above the stove were 175F at times. I had a certified HVAC guy tell me then they happens a stray spark can make the joist catch fire like it was doused in liter fluid. I digress...

Why do you say that??
Because, using only half of the firebox means you only have half the available fuel and if you are getting 12 hours its quite remarkable. The only way that would make sense to me is if you had a really large coal bed. I just don't see <3 cuft of wood keeping a house 70F for 8 or 12 hours unless its 45F outside and you house is 1200 sq ft.

Hmmmmm.... now that makes sense... or at least the best explanation I've heard.
But it's the air being fed under the coal bed, and flowing up through it, that keeps the coal bed screamin' friggin' hot.
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Yes, that's why my Shenandoah would kick ass.