Understanding burn cycle and temperatures

[woodhog73]

Ok I'm still figuring out how I'm going to put a thermometer on my insert. Probably a magnetic one on the exposed top or door and one on the metal liner. But haven't gotten to it yet.

So I always thought I could gauge stove temps decently by the visible condition of the fire. But now I'm not so sure.

So I burn mostly oak. It's very dry well over 2 years. This is dense wood and has high BTU. But when I get a good fire going and throttle back the air until I get very little to no flame with just secondary combustion, I get LESS heat than under the same circumstance when burning less BTU rich birch or popler. Of course my oak burns 3x as long but the heat drops off more where as the softer wood burns hotter with less air.

How is this ?

And at coaling stage. If I have heavy coaling, I open the air completely at coaling stage to help burn them off a little before putting in more splits. When I do this I sense the coals getting brighter so I assume hotter. But when all you have is coals left, know matter how bright orange they are how much heat really is being put out ? Do stove temps drop considerably at coaling even with the air wide open ? One would think hot coals put off a lot of heat. Is opening the air fully to burn off a heavy bed of coals a good idea ? Remember I don't have a thermometer to monitor temps when doing this

Sorry for what may be an odd set of questions. I really need a stove thermometer. Yet some people I've talked to say don't bother with it just use your senses based on the visual condition of the flames and coals.

 

[edyit]

I really need a stove thermometer. Yet some people I've talked to say don't bother with it just use your senses based on the visual condition of the flames and coals.

get 2 thermometers, one for the stove top and one for the flue, think of them as the tachometer and speedometer on your car, you don't need both but they make driving it so much easier

 

[Dix]

When I first started burning the PE, I didn't have a thermo and tried to judge my temps by eye. Turned out I wasn't very good at it, as what I thought was hot enough, really wasn't. Ended up clogging my new chimney in about 3 months (another culprit being sub par firewood, a usual first year problem).

With the thermo, I am able to get a quicker idea as to temps, and what's going on, and can make needed adjustments quicker. Life is wayyyy better with a thermo. So much so, that when the 13 went in, I had 2 thermo's ready for that puppy. Made figuring out the 13 a lot easier & quicker.

But when I get a good fire going and throttle back the air until I get very little to no flame with just secondary combustion, I get LESS heat than under the same circumstance when burning less BTU rich birch or popler

This sounds, to me, like the oak is not quite seasoned, or the air is getting cut back to soon. Has the oak been C/S/S for 2 years ?

 

[nola mike]

get 2 thermometers, one for the stove top and one for the flue, think of them as the tachometer and speedometer on your car, you don't need both but they make driving it so much easier

Can't really do that with an insert. I use a candy thermometer in the air gap to get an idea of the relative temp of the stove. No way that I can tell the temp by what the flame is doing. You answered your question about the hard v. soft woods. The soft woods will often give up their BTUs quickly, though the ultimate temp that you can get out of the different types of wood should be similar. The other variable aside from moisture would be how big the splits are. Smaller splits=quicker/hotter fire. Coaling is always tough. Cutting the air back too much/too soon/unseasoned wood will do it, but coals are just a part of the burn. Coals give off good heat, but not as much as in the off-gassing phase. The most efficient use of those BTUs is to keep the air relatively low. Opening the air will get it to burn hotter, but more of the BTUs will go up the chimney.

 

[woodhog73]

Coals give off good heat, but not as much as in the off-gassing phase. The most efficient use of those BTUs is to keep the air relatively low. Opening the air will get it to burn hotter, but more of the BTUs will go up the chimney.

Thanks for replies

When you say off gassing do you mean when there is active flame ( or smoldering ) from remaining wood ?

So there's no debate on coals they are for sure producing less heat than a low burning fire ? Meaning opening air on hot coals will provide less heat output than closing air on open fire with wood remaining ? So in that case I'll just keep the air low even during coaling stage if theres no real heat to gain I mine as well extend the coaling stage as long as possible?

What I've been experiencing ( red oak mostly 2 1/2 years seasoned it's dry ) is this. Splits roughly 4 to 5 inches around. I can fit 4 splits east west loaded. I get around 3 hours of flame both from the splits and secondary combustion. Then another 1 to 2 hours of coaling or more if I keep air low during coaling. So if coaling is part of burn cycle I'm getting around 5 hours total

 

[mark cline]

Here is my 2 cents . First I would want to know what the flue temperature is . A probe thermometer with a display near your stove. I know its an insert , but i would want to know the temp of the flue gases. Get a moisture meter and be sure the moisture is 20% or less . Mix in a few splits of of your birch or another species with the oak.
Is the stove putting out enough heat ? Do you want longer burn times ? Is the flue clean , only powdery creosote?

 

[kennyp2339]

Hmmm, I'm thinking your feeling (2) types of heat a different air settings.
While burning at higher air settings your getting good secondary's and a fire box filled with flames so your feeling the radiation of the flames through the stove glass and the convective heat coming from the stove body, you are also sending more heat up the flue.
When burning on a lower air setting your maximizing the stoves engineering burn, your wood is off gassing great, charring good and your secondary's are re-burning (this is how the stove burns as designed)
As far as coals just burning, yes they put off heat but you have to wonder why you have lots of coals there to begin with, stoves that produce tons of coals are either being ran way to hard, or heat is being robbed from the fire box by either less than stellar seasoned wood, to strong of a draft sucking heat from the firebox, or heat simply being robbed through radiation of the fire box (think masonry heat sink)
* take my setup - I run a bk princess, before that I ran a us stove 2500, when the 2500 was up stairs in my main living place the thing blasted me out of the house, I would only do half loads and would hardly have any coals left after the burn settle down, I got sick and tired of the wild temp swings so I moved the stove into my un-insulated block wall basement.
When I re-installed to 2500 in the basement my burns suddenly got whacky, I hadn't changed the wood supply but I suddenly became a coal farmer, I figured it was because I added an extra 10ft of chimney length, so I installed a pipe damper, figuring it would slow the draft down and keep more heat in the fire box, it did work to an extent.
I changed the stove out to a BK princess and figured that the coaling problem would be over with the BK t-stat technology, I was half right, the thing is, is that when it gets cold out (below 20deg) I lose about a 1/3 of heat through my block wall foundation, the t-stat should be tripping on a lower setting but it can't due to the room no getting up to temp, hence I tend to have more coal build up.
Now my buddy has a NC30, in his first house his nc30 produced tons of coals also due to the same heat transfer problems, his nc30 was in a stone fireplace, un-insulated, when he moved into the new house (with tons better insulation) he installed the same stove, he now burns at low air settings, hardly has any coal build up and just basks in heat all day.

 

[woodhog73]

Lots of good thoughts thank you.

I am planning on putting a probe thermometer on the flue just haven't gotten around to it.

What I can say is I posted a picture recently of the flue connection in a different post and one of the sweeps well known here commented that there was no discoloration of the liner and it didn't look like it had ever gotten that hot.

I'm very happy with heat output. It cranks out heat. I would like longer burn times than 3 hours of flame and 1 or 2 hours of coaling. But I've just become accustomed to it and assumed being a non cat stove this is the best I can't get. Total of 4 to 5 hours of heat capability out of one load.

I really was most interested in finding out if the coals are giving heat similiar to wood burning and if I should open air during coaling and I think I understand it better now.

As for the coals I do get. I'm not sure what a normal amount is. I don't have a moisture meter but I'm pretty experienced with wood and firewood processing. This stuffs got to be well under 20 percent. It's very light weight , turned brown, and when you bang two splits together it sounds hollow. For oak, the splits weigh nothing after 2 years in the sun.

My stove does draft well probably too well. I don't need the start up air to get a fire going. Even during shoulder season on a 50 degree day I get great draft. Better draft when it's cold out.

So based on what you guys are thinking, and I agree now that I'm thinking on it, I probably have strong draft and some heat loss elsewhere. Since I know my wood is dry I can't imagine anything else.

So at the end of the day is a 4 to 5 hour burn cycle including coaling reasonable for a small 1.9 cubic foot non cat stove ? Or should I be getting 6 to 8 hour burns ? I'm happy with the heat output.

 

[jatoxico]

Coals don't give me as hot a stove top as when there's active flame but a good coal bed will still give useful heat for some time. It all depends on the size of the original load. I like to turn the air up during the late stage to burn off the remaining coals/wood cleanly and to keep the heat up. I rarely (never?) see an actual rise in stove top temp but I do think with the added air and the coals burning down quicker the temp stays up higher as I burn through them.

 

[mark cline]

Just a thought here , my Mansfield produces a tremendous amount of heat .For me an 8-10 burn consists of the main room where the stove is , gets up to 76-78F. The kitchen and bedrooms down a hallway are cooler but comfortable .After 8 hrs (20F outside) , the main room would be about 66-68F and the other rooms proportionately cooler . I get about a 10 degree temperature swing over the 8-10 hr period. The only way to get more consistent temps. , would be to tend to the fire every 4 -5 hrs. On the other hand, a pellet stove would give a more constant controlled heat output due to the continuous feeding of the pellets . Temperature swings are all a part of heating with wood , added insulation will help to reduce the swing.

 

[kennyp2339]

On the other hand, a pellet stove

I feel a captains mast coming up if you mention this pellet thingamigig one more time lol, just good clean fun.