Larger stove and smaller burns.

[Roospike]

Brotherbart asked about larger stoves and burning smaller fires so i thought i would branch this thread off from the "Falling creosote" thread.
https://www.hearth.com/talk/threads/5724/

[quote author="ozarkjeep" date="1170382039"]I was told that at a local stove retailer also, "better to have a small stove and burn it hot, than a large stove dampered down"

But, could you not use a large stove, and build smaller fires and let them burn hot?

then if you NEEDED the full output you would have it? [/quote]

Exactly.

How does one tell if there stove it too big ?
You cant run the same size fire year around , it dont work like that. I dont need to full size of my firebox 75% of the time (3.0 cf) but when it gets 15° and lower the large fire box is needed. Woodstoves dont work like you home furnace and put out just one set BTU and then turns on and off as needed. One have to have a wide range of heat output from there stove to heat there home from 50° through -15° and with a wood stove your have to have different size fires , different loads.

This is an issue of so many people under sizing there stove and cant get the proper heat out put when it gets really cold , they run out of stove / size / fire box and it also shortens over night burn times.

 

[Roospike]

.

Gotta ask though Spike. What is the secret to getting the big firebox stove burning clean without cooking off a lot of wood with extra primary air to keep it clean without getting the big boy up to hot surface temps with smaller loads?

Build a "cave" ..........................

Build a cave out of the wood to keep a hot pocket with in the wood , after you have a normal coal bed going I place 3 small splits with in the fire box with 2 on the bottom and one diagonal across the top , it make a hot center with less air and the wood doesn't smoke , The top split will burn a little faster then the other two but once that all get burning and the pocket get hot your past the smokey start up.

The reason for the top split to be loaded diagonal across the top is #1 it lets more flames out from between the logs and #2 after the fire gets hot and all the splits get burning really well the corners of the logs burn away and the top split falls between the other two splits and and then burns normal and doesn't burn the top split away so fast.
(helps increase burn time)

I can do this with two splits also you just lean one split up against the other to make the cave.

**Picture shows three small 10"-12" splits with coal bed pulled up to 60% towards the front.
Wood load time of burn shown: approximately 2 minutes.
/ Damper setting 30%
/ Damper turned down on load shown to 10% after 6 minutes.

 

[Roospike]

.Wood loaded as per drawing.

 

[Roospike]

This is where the mass of the stove comes in , when burning smaller loads its likely your needing less heat so after the wood burns down to coal the heat off the fire box keeps throwing off good heat so even tho you might only get a 3-5 hour burn you still get heat coming off the stove for another 4 hours.

It depends how much heat you need as to how often you reload the fire box.

Coal beds:

You can load the fire box as shown the same way when wanting to burn off larger coal beds. The splits farther apart on the sides with a wider flat split does the better job to do this..

 

[Roospike]

First pic edited to show outline of splits..

 

[wg_bent]

Spike IS the master. He's right on all accounts. The one place I would disagree on stove size is over in the thread on a stove with a big fire view was desired in California. That person really wanted to look at the fire going, and my take would be that they really would cook themselves out of the house. If you live in a reasonably cold climate, bigger is better if you're mostly looking for heat.

Cost could be another concern, but in reality, Spike's Summit was only about 500(??) more than my Osburn, so small potatoes in the long run.

The teechnique of criscross like Spike said or a cave (so easy even a hogwildz ...er... caveman could do it ) will create a small but very hot fire but with a shorter overall burn time and less overall heat. Those fires are a bit more peaky than full loads, but you could even that out with a soapstone stove. My stove will get quite hot at first, then drop off and even out after that. Another thing to do is pay attention to the type of wood. 3 splits of oak done like Spike says will give you a longer burn and coal stage than white pine.

Burning a wood stove is a bit of an art form. That's part of the fun. Not too many people around discussing the nuances of their Burnham oil fired boilers.

 

[PAJerry]

Type of wood makes a big difference. We burned pine in the fall - good for short, hot fires to take the chill off. After that, we went to hardwood slabs, which gave more heat but not a real long burn time, so you could let things cool off a bit. Now, with the 0 temps, we are burning hardwood splits for lots of heat and a long burn. Wood burning is not exactly a 'throw it in, if it burns, it's good' proposition if you try to do it right.

 

[Andre B.]

The teechnique of criscross like Spike said or a cave (so easy even a hogwildz ...er... caveman could do it ) will create a small but very hot fire but with a shorter overall burn time and less overall heat. Those fires are a bit more peaky than full loads, but you could even that out with a soapstone stove. My stove will get quite hot at first, then drop off and even out after that. Another thing to do is pay attention to the type of wood. 3 splits of oak done like Spike says will give you a longer burn and coal stage than white pine.

Burning a wood stove is a bit of an art form. That's part of the fun. Not too many people around discussing the nuances of their Burnham oil fired boilers.

You will also, at least I don't, not get the same kind of secondary burn action, which will throw some people off. With a small fire even with the "cave" I have to keep the primary open more to keep the fire going which drops the burn back closer to what you get in non EPA stoves. And since the secondary air does not get cut back efficiency is going to suffer some, more excess air which gets heated and sent up the stack.

 

[Martin Strand III]

What is being discussed is the "Partial Charge Efficiency" of a stove; one of four "efficiency" factors which goes into determining how much heat is actually transferred into the room, over and above operator factors.

Most realize high temperatures are needed to avoid smoldering conditions. Some stoves handle smaller fuel charges better than others. A little voice is telling me it may have something to do with the mass of the stove (from scratch, a 55 gal drum will heat better from a small fuel load that a 650 lb cast iron beast).

Has anyone discovered how to determine partial charge efficiency of a stove except by trial and error?

Aye,
Martry

 

[Larry H]

I'll definitely agree with all of the above that is posted here. This seems to be where the art of being a good woodstove operator comes into play, as you need to put in some time through trial and error to find out what the stove needs and balance that with your heat needs and burn as cleanly as possible all at the same time. Really it's what we all should be striving for if not already doing. Spike is a master at this.

 

[KarynAnne]

What is being discussed is the "Partial Charge Efficiency" of a stove; one of four "efficiency" factors which goes into determining how much heat is actually transferred into the room, over and above operator factors.

Most realize high temperatures are needed to avoid smoldering conditions. Some stoves handle smaller fuel charges better than others. A little voice is telling me it may have something to do with the mass of the stove (from scratch, a 55 gal drum will heat better from a small fuel load that a 650 lb cast iron beast).

Has anyone discovered how to determine partial charge efficiency of a stove except by trial and error?

Aye,
Martry

Funny you should bring that up. I've just been wondering that about my Jotul. Here's the trick that I've just learned this week to keep my temp high, my reloading foolproof and my disposition sweet. I get a hot fire going in the AM and let it run for a bit (my brother says this will help a little w/ overnight low and slow creosote issues). Once it's up to speed and has run for a while (around 500, or 600 if I'm lucky) I'll throw 1 good sized split in there. That's the only time I don't have to fiddle with the stove. I let it go for a good while after backing down the air flow, but try to catch it before the stove gets much below 450 to add another decent sized split. This keeps me fiddle free all day! Whooppee! BUT - I have to be here all day to kind of "catch it" at the right time. If this stove goes below 350 - forget it, I'm going to end up cajoling that thing (begging sometimes) to go ahead and burn. I have not noticed burning any more wood during the day than I already have been.

This stove burns WAY better by the above method than by fully loading. Fully loading is almost guaranteed to kill it, at least for me. And this is supposed to be a fairly large stove. Overnight burns - I have a really hard time getting the temp up past 400 (sometimes even up TO 400) before I shut it down for the night. In the AM my front glass is not blackened, but that stove has not been at high temps overnight that I am aware of.

 

[Rhone]

Well, I'm on the same page as Marty S with the partial charge efficiency. I have not gotten 3 splits to produce any significant amount of heat, but I'm open to ideas as it's something I've tried countless times and failed. The only way I've gotten 3 splits to work in my unit is after I've already warmed it up and have a huge pile of hot coals I can put 3 splits, sometimes even 2 and poof instant fire and away we go. But, to me the huge piles of hot embers is acting like another log and cheating.

I've probably attempted to get heat out of 3 log splits from a cold start about 60 times. I have a 2.4 cu ft firebox and it's soapstone lined. Here's pretty much what happens, and I have a side/side unit.

3 splits loaded in sort of an arch pattern, with the 2 on the bottom and the top one placed to seal the gap in the middle to create a cave. This has been the worst for me, the top log prevents flames from reaching up to the secondary burn tubes and produces a lot of smoke, most often it doesn't warm my unit up enough for the fans to kick on. Raises the house temp 0F.

3 splits loaded like Roo, 2 on the bottom the top placed diagonally. Takes 2 1/2 hours before fans turn on, they stay on for a couple hours, raises house temp 1-2F.

3 splits loaded with 1 in back, 2 in front. This works better for me with my side/side unit, the 2 front logs in the front insulate forcing the heat to stay in the firebox longer. Warm up time is about 2 hours, blowers stay on for about 2 hours, and will heat my house 2-3F.

4 splits loaded 2 in back, 2 in front. I have to keep an air gap between, but this is what I call the minimum load. Warm up time is a little under an hour, blowers stay on for 6-8 hours, and will heat my house 8-10F. Compared to any of my 3 split configurations, it's more than double the heat output by adding just 1 split and why I call it the minimum load, 3 splits can't seem to get things off the ground, not from a cold start anyway.

5 splits loaded 3 in front, 2 in back. This configuration adds little over the 4 split. The exta split in this configuration is so close to the front and so high, that as it burns the flames loop around the secondary baffle and go up the flue making the extra log split add very little. I've found this configuration to be the same as above.

5 splits loaded 3 in back, 2 in front. This is the better configuration as the extra log in this case the flames don't bypass secondary burn, and the extra log is placed in a spot that makes the flames & smoke have to take one of the longest distances before exiting. Warm up is just under an hour, blowers stay on for 7-9 hours, and will heat my house 9-12F.

6 splits loaded 3 in back, 2 in middle, 1 in front. This is the most difficult configuration to get started with kindling and get secondary burn going. In this configuration the wood is stacked tight, and for secondary burn to occur the flames have to reach around the pile on the bottom, go up the sides, and then loop over the top. But, is the most efficient. Warm up time is just over an hour, blowers stay on for 10-12 hours, and will heat my house 13-18F. This is the new configuration I've been trying to master. I've been loading up 4 splits at noon, and another 4 before bedtime. However, this configuration lets me start at 6-7pm it will heat my house until 6-7am, and saves me 2 splits. At 6-7pm my house is usually 61-63F, in the evening around 9-10pm my house reaches around 73F-75F, and in the morning (7am) it's usually 67-69F.

 

[slowzuki]

I have grown up on non-epa air tights from small to large and currently have a small one. From my experience with the largest one, it is useless for small fires except under a few conditions. With small fires, too much excess air moves through the stove, bypassing the fire. The fire can't heat the fire box and brick up enough to get a good clean burn started so it smokes and smoulders away unless it is a load a finely split dry softwood.

The only way I have ever found around this is to reduce the size of the stove. How? Well, in warm weather I let the ashes build up in the stove so the volume is smaller. I move them to the other side behind the unused door (closing the damper on the door of course.) The other method I use is to keep fat, not well dried, unsplit rounds available to pop in one side of the stove. It is really acting as a big plug and if you set it down well into the ashes and it is the right length (close the damper on that side btw) it will remain in place for up to two days. This lets me build a nice hot fire on the other side of the stove.

The best comprimise I have ever had was a non-airtight that front loaded from a single door and had a long narrow fire box. For big fires you loaded the whole length, small fires you just built the fire in the front and the hot gases passed through the dead space at the rear.

 

[precaud]

I’ve probably attempted to get heat out of 3 log splits from a cold start about 60 times. I have a 2.4 cu ft firebox and it’s soapstone lined....

Rhonemas, your stove's firebox lining is very high mass, I think that explains why spike's technique doesn't work for you. Fireboxes with lighter insulating material (the pumice-looking firebrick, and ceramic board baffle) come up to operating temperature very quickly - as little as 5 minutes, even.

Another thing that could make a big difference is if the stove has a front bed-level air source or not. The jet of air they provide will easily feed that log geometry. But an airwash-only primary may not.

 

[Rhone]

I think you're right precaud. Firebrick is an insulator soapstone is a transmitter I think is what Marty S called it once. Once it gets warmed up reloading is awesome, even with just a few coals adding a couple logs it's like "Poof!" instant full fire, scares the heck out me sometimes when I add them in and I get secondary burn going on before I've even had time to shut the door. But, trying to get a fire moving with just 2 - 3 splits from a cold start has not been productive. I think you're right, soapstone has even heat, should never need replacing, and great on reloads but with small loads you need the insulating & speed properties of firebrick. Though, I just need 4 splits and they can be 13" long in my 21" wide firebox and will do just fine. I think it's because the 4 splits stacked up with a flame inbetween, the wood acts like an insulator and helps reduce the effects of all the space inside. Though, you mix in a lot of air and don't get the heat out of it.

 

[precaud]

Firebrick is an insulator soapstone is a transmitter I think is what Marty S called it once.

Stop! You're both right! It's a toothepaste AND a floor polish! (Thanks Firesign Theatre)

Both CAN be a "transmitter" but not until they warm up. As you noted, it just takes alot longer for the soapstone to get there.

 

[ozarkjeep]

There is alot of good information here.

one observation though, a couple of folks have said a small fire in a large firebox wont work, wont get hot, thigns to this effect.

define small fire? is it the 3 small splits?

Maybe I should have said a medium fire in a large stove?

of COURSE there will be such small fires that no heat is produced, this was not my point.

I meant, a reasonable fireload for a smaller fire box, would still burn and make heat in a larger fire box. I AM NOT talking about 3 peices of wood the size of your thumb.

POssibly also the secondary burn plays into effect here too.

Ive got a cat stove, I get secondary burning all overthe stove, in front of the cat, on the glass, on the inner stove surfaces, ONLY when the firebox is really hot ( obviously)

but, I can get the cat to ignite whether the fire box is hot or not ( within reason, it doesnt need to be NEARLY as hot as it does for secondary action)

The example posted above of 3 small splits in mine would glow the combustor and put my center stove top at 700+ degrees with the air left open , if properly placed within the stove.

 

[Martin Strand III]

I have grown up on non-epa air tights from small to large and currently have a small one. From my experience with the largest one, it is useless for small fires except under a few conditions. With small fires, too much excess air moves through the stove, bypassing the fire. The fire can't heat the fire box and brick up enough to get a good clean burn started so it smokes and smoulders away unless it is a load a finely split dry softwood.

The only way I have ever found around this is to reduce the size of the stove. How? Well, in warm weather I let the ashes build up in the stove so the volume is smaller. I move them to the other side behind the unused door (closing the damper on the door of course.) The other method I use is to keep fat, not well dried, unsplit rounds available to pop in one side of the stove. It is really acting as a big plug and if you set it down well into the ashes and it is the right length (close the damper on that side btw) it will remain in place for up to two days. This lets me build a nice hot fire on the other side of the stove.

The best comprimise I have ever had was a non-airtight that front loaded from a single door and had a long narrow fire box. For big fires you loaded the whole length, small fires you just built the fire in the front and the hot gases passed through the dead space at the rear.

By Jove, I think Newb Slowz has got it!

For smaller fires in a larger stove, why not temporarily decrease the size of the firebox by adding a couple layers of brick shaped as a rectangle? Or, add a 6" - 8" piece of 12" square chimney ceramic or similar? For anyone seriously concerned, I'd give it a go.

Aye,
Marty

Grandma used to say, "Don't work harder, work smarter."

 

[Andre B.]

There is alot of good information here.
one observation though, a couple of folks have said a small fire in a large firebox wont work, wont get hot, thigns to this effect.

Don't think anyone said "won't work" but more along the line of won't work as well. Emissions in terms of grams per BTU delivered to the house will go up with an undersize fire, also with a fire that is too big for the stove. And efficiency will go down some, higher percentage of excess air taking heat up the stack and fuel gases that cool off before they can get burned. It will still work you just have to realize that it is a compromise.

Question.
Have there been any studies of what the emissions of and EPA stove are in the real world?
Like monitor the stacks 100 percent of the time for an entire season on say 100 or 1000 installs and compare with the EPA numbers for those stoves.

 

[Martin Strand III]

Question.
Have there been any studies of what the emissions of and EPA stove are in the real world?
Like monitor the stacks 100 percent of the time for an entire season on say 100 or 1000 installs and compare with the EPA numbers for those stoves.

Stick around. Big Brother may well be doing this for all of us shortly. It may have started already on West coast with restricted burning bans....

Aye,
Marty

 

[precaud]

Question.
Have there been any studies of what the emissions of and EPA stove are in the real world?
Like monitor the stacks 100 percent of the time for an entire season on say 100 or 1000 installs and compare with the EPA numbers for those stoves.

Andre, I haven't seen anything exactly like you describe, but last winter while googling for something else I did come across a followup onsite emissions test of some EPA stoves that had been in use for a couple years, either in OR or WA. As one might expect, some stoves fared better than others. I seem to remember 75% of them still were in spec.

 

[HalJason]

Question.
Have there been any studies of what the emissions of and EPA stove are in the real world?
Like monitor the stacks 100 percent of the time for an entire season on say 100 or 1000 installs and compare with the EPA numbers for those stoves.

Andre, I haven't seen anything exactly like you describe, but last winter while googling for something else I did come across a followup onsite emissions test of some EPA stoves that had been in use for a couple years, either in OR or WA. As one might expect, some stoves fared better than others. I seem to remember 75% of them still were in spec.

Falling a bit off topic here, but I'm curious.

What would cause an EPA stove to fall out of spec? Assuming everything is kept clean, I'd assume a non-cat stove to be pretty rock steady as far as emissions goes. A cat stove would obviously change as the cat ages.

Maybe we're just looking at operator ignorance? (clogged cats, bad gaskets, poor chimneys, destroyed secondary tubes etc...)

-Hal

 

[Henz]

yes, I had the Avalon rainier whcih is the smaller Avalon. Loved the stove but didnt heat the house like I had thought it would and I definately wasent happy with the burn time.. traded right up (after three months) to the big Olympic and am glad that I did.Almost 2x the firebox size..When I relly chuck it full of hardwood (thats all I burn) I can really get the house up to temp and one that sustains much longer..At night, I can achieve a 7-9 hour burntime with no problem and sometiems even more depending on outside conditions.
I would say that you need to really get to know how the stove reacts to how you load it, the type of fuel and how you damper it...IT takes time

 

[Martin Strand III]

Halj and Adirwoodburn are talking a bit about operator factors and how that affects stove performance. We buy these technical machines (stoves) and use and abuse them. Where one is on the "use" learning curve has a lot to do with how happy we are with them.

Well, I posted something to that effect in another thread, and, while dodging thrown rocks there, it read something like this:

“Heating efficiency of any wood heater depends on 2 (well, really 4) factors:
(1) Combustion Efficiency - how completely it burns the wood and
(2) Transfer Efficiency - how much of the fire’s heat gets into the room rather than going up the flue.
[3 - added] Linearity of Output - how a stove's heat storage capacity handles a hot fire w/o overheating the room
[4 - added] Partial Charge Efficiency - how a stove handles small fuel loads

How efficient your wood heater operates depends on 2 more factors:
(1) Installation - location on outside v inside wall. Heater too big for house? Flue draw?
(2) Operation - Wood is how dry? % Firebox load? Adequate air? Clean, well maintained?

Your operating technique accounts for the largest variations in your woodstove’s heating efficiency.”

www.baaqmd.gov “Woodburning Handbook”

Aye,
Marty

 

[Henz]

I agree with thost statements..However if you are burning green wood you need to have your head examined.