Long Burn vs Efficiently

[Whitespider]

That extra reburn secondary combustion that is claimed at 30% really does become available in the real world... ...Ask anybody that has a EPA stove.

Ask anybody?? Anybody?? Does that include me (and a few others I can name on this board)??
Numbers, specifications, and whatnot rarely coincide with the "real world"... just ask anybody
*

 

[mopar969]

I agree it seems to be mixed results. Most agree with flotek but some of us still like the older pre epa versions.

 

[cheeves]

I've run a Tempwood wood stove (downdrafter) since 1977 and wouldn't trade it for any EPA stove I've seen!
Friend of mine installs woodstoves and liners for a living and agrees with me.
I've seen other stoves. Another friend of mine that just retired had a stove shop, and I used to hang out in there. At best catalytic stoves improve PM's maybe 5-7 %! For the money they cost I can't see where the money they get for these stoves today justify the expense.
My recent Tempwood cost me $50, and my original one I bought in '77 cost $325. They work like a charm and produce great heat for 6-8 hrs depending on the wood I load it with.
I'll keep my Tempwood, and keep burning it until I die!!!

 

[mopar969]

Nice cheeves!

 

[Whitespider]

It's really as simple as that, despite the bloviation to the contrary.

OK smart azz... how big do I need??
*

 

[Chris-PA]

Well, since no one else has... I guess I'll go ahead and bring this up.
One qualifier before I start... I'm talking non-cat stoves, I have never used a cat-stove and wouldn't have a clue.

The article quoted by the OP eludes to something I've mentioned before. I've read the EPA test procedure several times, and I simply cannot find where "heat" or "time" is measured in any way shape of form. The only thing actually measured and quantified is per hour particulate emissions; which makes sense when you think about it... the EPA is (supposedly) concerned solely with "protecting" the environment, but in no way concerned with heating your home. The "efficiency" rating attached to a certified stove by the EPA is simply the combustion efficiency... the stove could actually dump 100% of that heat out the flue and still receive and 80% efficiency rating from the EPA.

Now, I won't argue that burning 30% more of the available fuel (in this case a portion of the particulate emissions supposedly not burned by a smoke dragon) will result in more heat... it flat has to result in more (generated) heat from the same amount of fuel loaded in a box. What I will argue is whether-or-not you receive, or realize, all of that extra heat in your home. Lot's of things determine the amount of "heat" exiting, or "lost", through the flue, but the three major ones are;

• The amount of air entering the box - More air (gas) entering has to equal more gas exiting, and those exiting gasses are hot... they carry heat with them. I only have extensive experience with one make and model of EPA certified stove... but that one model required more air and the flue ran hotter than any "smoke dragon" I've ever used. Admittedly nothing measured, just perception and "feel"... but c'mon, holding your hand by the pipe is pretty a damn good comparison. I actually ran the "stovace" circulation blower with a snap disk mounted a few inches away from the flue pipe, I couldn't do that with the prior "smoke dragon". I've read here from users both ways, some say their EPA stove pipe runs cooler, some say hotter; but the temperature of the stove pipe is near 100% user controllable with an "air tight" box... so what users are experiencing doesn't mean much. I mean, using a flue damper with the old dragon I could touch the pipe above it at times (when I tried the flue damper with the EPA box I could also reduce pipe temp somewhat, but not to the same extent without killing heat output). Secondary burn stoves need secondary air, they need more air (or mine did); if more air is entering, a greater percentage of the generated heat must be exiting (if all else remains equal).
• The temperature of the fire - Again, if all else remains equal, a hotter fire will make for hotter gasses exiting the flue... i.e., proportionally more generated heat lost through through the flue. A hotter fire also means faster combustion... and there ain't any magic to get around that. The secondary combustion stoves increase fire temperature by pumping more of the above mentioned air in, insulating with refractory brick (ain't the same as true "fire brick"), and whatnot (I understand there are exceptions, not all have brick). The EPA certified, secondary combustion stoves use more air and an insulated box to increase combustion rate, thereby increasing heat, thereby increasing combustion efficiency (or, at least mine did). Again, if all else remains equal, there ain't any magic to get around the fact that a hotter fire will burn faster, and put proportionally more generated heat out the flue. If all else remains equal, a 30% increase in combustion efficiency cannot equal a 30% increase in heat transfer to the room... at best, maybe half that.
• Stove design - This is where all else does not remain equal. For example, you can add a highly efficient heat exchanger to extract more of the generated heat before it exits. But that has nothing to do with combustion efficiency, it's just a more efficient heat extraction method (i.e., heating efficiency). A highly efficient heat exchanger can be added to a non-EPA certified box also... but because of the (supposedly) dirtier burn, it may require cleaning more often. Yeah, the combination of more efficient combustion and heat extraction will result in more realized heat... but now things are equal again, and you won't realize 30% more heat... maybe half that at best. The "secondary heat chamber" in my DAKA furnace is nothing more than a crude heat exchanger... that, because of design, doesn't require cleaning.
  Another example is an IR transparent glass door... and this is where my application(s) fell flat. My PE stove has an insulated firebox, the floor, both sides and the back. The "flame stage" (the stage when most particulate emissions are generated) of my PE is fast, damn fast... causing the fire to collapse into coals pretty damn fast. At the coaling stage the box actually "smolders" the fire by passing air over the top of that coal bed, and because the box is insulated it relies on the glass door to transfer the low heat into the room via IR radiation. That's great if the stove sits in a room full of solid surfaces, and would likely increase "usable" burn (heating) time. The problem with that, for my application as a "stovace", I needed the heat transferred via conduction to the forced air... and that's why removing the fire brick (insulation) helped some. And another problem with IR radiation is it passes through air without warming it... it needs to be absorbed by something solid, which in turn warms the air by conduction. The "glass door" design falls on it's face in my shop also, because even though it ain't all that big, it is open... there flat ain't anything to absorb the IR radiation (other than the cold walls).
  Now possibly a different design EPA stove would work better... such as a cast iron, non-insulated design. But even so, the IR radiation escaping the glass is basically wasted heat for my applications. "Smoldering" the coal bed to increase burn (heating) time actually cause me to burn more wood, for a net of less usable heat, and shorter (perceived) burn times.

So I go back to what I keep saying...
Combustion efficiency does not automatically equal heating efficiency (more usable, or realized heat). The (current) EPA certified designs are not always "more better" for every application. In fact, in certain applications the result will be less (realized) heat, more fuel burned, and shorter (perceived) burn times... resulting in more overall particulate emissions than a properly operated smoke dragon. Nothing in this world is a "one-size-fits-all" sort of thing... that ain't how it works. I can even extend this to another thread... the Tundra thread... it ain't so much the combustion efficiency that putting heat in your home, it's the heat exchanger (the more efficient heat extraction method) that deserves the credit. No doubt, from just holding my hand in front of the glass door during coaling, if my PE was sitting in a nice cozy den or family room filled with solid surfaces it would near heat you out'a the room on low setting, and likely go several hours without needing a reload to maintain that... but that's not every application, is it??
*

What they actually measure is the weight of the particulate emissions during the entire run (until the fuel is consumed), and the time to do that (however long it takes), and then calculate a rate of emissions (g/hr) from that. So effectively they are measuring the total unconsumed mass of wood. They don't rate heat output rate or efficiency or any of the rest of it. How useful or effective the stove is as a heating appliance is not their concern - it is an emissions test.

Nevertheless, these parameters are not independent. It's a fire - if more mass is burned, more heat (energy) is extracted. That energy must go somewhere. If the fuel load is consumed over a similar period of time, and more of the fuel load energy is extracted, then the rate of energy extraction is higher. Your hypothesis of how that energy avoids getting into the house is pretty contrived - that while the smoke dragon sends more of the fuel up the stack unburned the secondary combustion send the heat up the stack. You haven't a shred of evidence for this.

When my secondary combustion stove is cranking the total area of the air inlet is very small. The flue as measured by a cheap magnetic thermometer rarely gets over 400, and my flue pipes don't get all discolored, so I'm not buying that one. While the lower portion of the firebox is insulated (with actual fire brick), pretty much like your Spectrum, the upper portions are not. There is plenty of area above the firebrick (where the secondary combustion happens) to radiate heat. The purpose is to maintain high heat to cook off the gases from the wood over the coals, not to keep the heat from coming out of the box. Also, the greater the temperature the more efficient the transfer of energy (heat) is. So no, it isn't going up the flue and higher temperatures transfer heat more efficiently (i.e. at a higher rate).

The difference with these stoves is the different temperature (and therefore heat transfer rate) over time, especially if one doesn't adjust the air control. They extract more of the energy in the wood, and produce higher temperatures (and higher heat output) for part of cycle, but the output rate is not constant over the whole fuel load. A smoke dragon will send more of the fuel energy up the stack, but have a more constant output over the cycle.

 

[motorman1]

I'm no stranger to heating with a wood stove, but have no experience with the newer EPA stoves. I have a smaller Buck freestanding stove and fill it as much as possible with the damper wide open to heat my 1300' abode. Works fine, but I have to keep loading it every hour or so. I only use 2 year seasoned hardwoods. If I choke the fire down, the house cools down far too much for my comfort level and I'd be concerned of creosote build-up in the pipe. I just run it as hot as I can and use a bellows in the morning to revive the coals to ignite the "morning" wood.

 

[Bushmans]

I'm no stranger to heating with a wood stove, but have no experience with the newer EPA stoves. I have a smaller Buck freestanding stove and fill it as much as possible with the damper wide open to heat my 1300' abode. Works fine, but I have to keep loading it every hour or so. I only use 2 year seasoned hardwoods. If I choke the fire down, the house cools down far too much for my comfort level and I'd be concerned of creosote build-up in the pipe. I just run it as hot as I can and use a bellows in the morning to revive the coals to ignite the "morning" wood.

Does this stove have a baffle in it?
If it doesn't you should look into installing one.
1300 sq feet is pretty small to have to be loading it every hour or two. It must be really small!

 

[Whitespider]

Your hypothesis of how that energy avoids getting into the house is pretty contrived - that while the smoke dragon sends more of the fuel up the stack unburned the secondary combustion send the heat up the stack. You haven't a shred of evidence for this.
The flue as measured by a cheap magnetic thermometer rarely gets over 400, and my flue pipes don't get all discolored, so I'm not buying that one.

Hypothesis?? Evidence??
So we're back to magic again??
So... according to you, if all else remains equal (which I made more than clear), a hotter fire and higher firebox temperatures result in cooler gasses exiting the flue??
And your "evidence" for this is a "cheap magnetic thermometer" and the fact your "flue pipes don't get all discolored" ??

Well, I don't have the gadget, but my flue pipes don't get all discolored either‼
The only thing discolored pipes prove is that someone over-fired the appliance at some point... EPA certified or not‼
And I made it crystal friggin' clear that design and/or heat transfer method will effect both heat output and flue gas temperature... that's why I stated several friggin' times, "if all else remains equal"‼
*

 

[513yj]

Hypothesis?? Evidence??
So we're back to magic again??
*

Maybe someones magic can tell me how to get more heat outta this EPA stove I have when it gets a lot of coals other than shovel it out and chuck more solid wood in there. If I don't sit there and drink beer and continue to stir them around I can watch the thermometer in my house slowly drop.

 

[Whitespider]

Have you tried, "Abra-Kadabra"??
*

 

[firebrick43]

I find using a faster burning wood that doesn't coal as much helps as doe a couple of splits in batches opposed to filling the stove completely up every time.

I experience the same issue burning some American elm during the -20 days we had a couple of weeks ago but don't when burning cherry or maple when the outside temps are higher so my batches are further apart.

 

[Whitespider]

I find using a faster burning wood that doesn't coal as much helps as doe a couple of splits in batches opposed to filling the stove completely up every time.

How does that work when you're not around to "babysit" the box??
The application of a band-aid doesn't equal healing of the wound...
*

 

[Chris-PA]

Hypothesis?? Evidence??
So we're back to magic again??
So... according to you, if all else remains equal (which I made more than clear), a hotter fire and higher firebox temperatures result in cooler gasses exiting the flue??
And your "evidence" for this is a "cheap magnetic thermometer" and the fact your "flue pipes don't get all discolored" ??

Well, I don't have the gadget, but my flue pipes don't get all discolored either‼
The only thing discolored pipes prove is that someone over-fired the appliance at some point... EPA certified or not‼
And I made it crystal friggin' clear that design and/or heat transfer method will effect both heat output and flue gas temperature... that's why I stated several friggin' times, "if all else remains equal"‼
*

I never said that - it is you who try to relate unrelated things due to your lack of understanding of the things that are measured and the meaning of the data that is presented. You proposed that while the secondary combustion stoves send less energy up the flue in terms of unburned particulates, they send more heat energy up the flue as hot gases and so waste more energy, and that the EPA test results don't show this.

PROVE IT

By the way - with a radiative mechanism the rate of heat transfer is proportional to the 4th power of the temperature difference, while with conductive or convective it is only directly proportional. When a secondary combustion stove is on the secondary burn and very hot the rate of radiative heat transfer goes way up. If you blow a lot of air over the sides and keep them cool you kill the heat transfer rate and get cold.

Maybe someones magic can tell me how to get more heat outta this EPA stove I have when it gets a lot of coals other than shovel it out and chuck more solid wood in there. If I don't sit there and drink beer and continue to stir them around I can watch the thermometer in my house slowly drop.

Heat is energy, not temperature, not rate of heat transfer. In theory you could take a really long time to transfer the energy in the logs and transfer a really high percentage of the energy in those logs into your home, but never have the stove get very hot. It would be worthless as a heating device. If your firebox is full of coals the stove likely isn't very hot and isn't transferring energy at a very high rate, and so your house is cooling off.

A secondary combustion stove has a much higher heat transfer rate when the secondary combustion is happening. If the manufacturer rated the peak BTU/hr rate at that point, then when secondary combustion is over the output rate will be much lower and you will get cold. A peak BTU/hr rating does not imply that it does this continually, so you are better off to pick your stove based on the volume of the firebox.

If you plotted the rate of energy transfer vs. time for the two stove types, they would have different shapes (assuming they held a similar amount of wood). The area under the curve of each plot would represent the total energy extracted from the wood, and the secondary combustion stove would have a greater area (and may also take longer to finish). But late in the burn of a particular load it may have a lower output rate compared to the smoke dragon, especially if you don't stir the coals or adjust the air.

 

[Woody912]

I'm no stranger to heating with a wood stove, but have no experience with the newer EPA stoves. I have a smaller Buck freestanding stove and fill it as much as possible with the damper wide open to heat my 1300' abode. Works fine, but I have to keep loading it every hour or so. I only use 2 year seasoned hardwoods. If I choke the fire down, the house cools down far too much for my comfort level and I'd be concerned of creosote build-up in the pipe. I just run it as hot as I can and use a bellows in the morning to revive the coals to ignite the "morning" wood.

I am guessing your stove is just too small. I heat 1200 sq ft with a Grandma Fisher, I can easily make it 100 degrees inside with outside air temp of -20 and 30 mph winds. We had -19 3 days ago and house was low 60's when I got up and I had not really busted my butt to max loading the stove since forecast was not that cold. My stove gets opened up about twice a day, otherwise mostly stays on "keep fire burning" rest of the time

 

[philoshop]

My old stove keeps me comfortably warm with minimal fuss, doesn't use much wood, produces very little smoke, and has never caused complaints from my neighbors.
I'd like to keep it.

 

[Whitespider]

You proposed that while the secondary combustion stoves send less energy up the flue in terms of unburned particulates, they send more heat energy up the flue as hot gases...

And I never said that‼
I said if all else remains equal, a hotter firebox temperature means hotter gasses exiting.
It don't matter squat what sort of firebox it is, EPA or not, if ya' run the temperature in any particular firebox hotter, by any means whatever, the flue gas temperature also increases. And nothing short of magic can change that... and I certainly never claimed it wasn't true in a non-EPA box.

When a secondary combustion stove is on the secondary burn and very hot the rate of radiative heat transfer goes way up. If you blow a lot of air over the sides and keep them cool you kill the heat transfer rate and get cold.

I don't use radiated heat to heat the living area of my home, I use conducted heat‼ Radiated heat is, for the most part, worthless, wasted heat for my application... that was the whole friggin' point that you obviously missed‼ It does near no friggin' good to radiate heat into the cold concrete walls of my basement to just be transferred to the dirt behind it... when I'm trying to heat my upstairs living area‼ And it's the same in my shop... It does near no friggin' good to radiate heat into the cold board walls to just be transferred to the outside. If blowing air over the firebox "kills" heat transfer... how in hell is it possible that I heat the living areas of my home with a forced air furnace??

All you've done is say the same thing I have... but with some sort of blinding attitude.
I know the mechanisms of radiated and conducted heat... but it don't matter cold squat how much radiated heat comes off the box if it's going where you can't use it. I have no friggin' use for radiated heat in my application... none, nada, zilch, zip‼ Radiation does very little to warm air directly, it passes through it until it strikes a solid surface. In my applications, heat radiation (from the box) is near worthless, wasted heat‼ It could just as well not even exist.
So... why don't you explain why all this extra secondary burn heat radiation, a very large share of which is passing through the glass door and not even warming the box, is "more better" for me?? And when the secondary shuts-down, the fire collapses into coals, and the primary heat transfer method (in an insulated box) is radiated through the glass door... exactly how is that "more better" for me??
*

 

[firebrick43]

How does that work when you're not around to "babysit" the box??
The application of a band-aid doesn't equal healing of the wound...
*

My stove is a jotul f100 which is recommended for 1000 square feet. House is 1450 and has 2x6 walls and r60 in the attic. The stove is run full air 99 percent of the time unless hedge or strong winds cause an overheat. In a normal indiana winter we will fire it maybe 6 hours a day(2 hours morning/4 hours evening) getting it up to 75/6 and letting it die. Most of the time by the time wife gets home 6 hours after I have left the house has only dropped to 68 and the propane hasn't kicked on (66)

This year has obviously been different but my wife, an RN, has been called off work about 50 percent of the time (due to obamacare) so she keeps it going maybe 12-14 hours a day. The thick Slate colored tile floor around the stove helps tremendously absorbing heat to moderate the temp in the room and real ease it back when the stove is not running. We have thought about a larger stove for those -20 below zero nights but they are so infrequent and most of the time I would have to choke back the larger stove or overheat the room (wife doesn't mind but I DO) so I cheerfully put up with its small faults and enjoy its beauty, clean glass, no smoke, one handful of creosote and only using 2 cords of wood(in a NORMAL year).

 

[Whitespider]

(deep breath)
OK... I'll ask the question again.
How does, "using a faster burning wood that doesn't coal as much helps as doe a couple of splits in batches opposed to filling the stove", work when you're not there to "babysit" the stove??

 

[513yj]

Heat is energy, not temperature, not rate of heat transfer. In theory you could take a really long time to transfer the energy in the logs and transfer a really high percentage of the energy in those logs into your home, but never have the stove get very hot. It would be worthless as a heating device. If your firebox is full of coals the stove likely isn't very hot and isn't transferring energy at a very high rate, and so your house is cooling off.

A secondary combustion stove has a much higher heat transfer rate when the secondary combustion is happening. If the manufacturer rated the peak BTU/hr rate at that point, then when secondary combustion is over the output rate will be much lower and you will get cold. A peak BTU/hr rating does not imply that it does this continually, so you are better off to pick your stove based on the volume of the firebox.
.

We covered heat already. Temperature in the house is raised when energy (heat) moves up the concentration gradient (inside stove to outside stove). Heat cannot move fast enough in brutal cold when coals build up in an EPA stove for my liking. It might work over there in PA where the outside temps are warmer but here in the UP it dont't cut it with the weather we've been having.