Max Heat Output

[nola mike]

Unfortunately, I don't have sufficiently sized stoves in either of my homes. Had to flee richmond this week because we've been without any running water (thanks DPU and political appointments!). Anyway....
Fairly cold this week (lows in the teens, highs upper 20's, 15 mph wind to exposed house). House temp 45' on arrival. It takes a *long* time to get up to a comfortable temp. So best burning strategy? I should know this by now, but I'm initially running my air initially to get max heat output, turning it down as low as possible while maintaining that output.
Question is, how to best maintain output from there? My thought is that I should open up the air as soon as it's more or less finished off gassing and the stove temps start to drop. Still above the coaling stage at this point. I think that this results in a shorter/less coals coaling stage, which allows me to reload faster. The whole rearranging coals/putting a split on there thing might work somewhat, but keeping the door open long enough to rearrange coals cools it down significantly, and IMO doesn't get rid of the coals as quickly.

 

[EbS-P]

Unfortunately, I don't have sufficiently sized stoves in either of my homes. Had to flee richmond this week because we've been without any running water (thanks DPU and political appointments!). Anyway....
Fairly cold this week (lows in the teens, highs upper 20's, 15 mph wind to exposed house). House temp 45' on arrival. It takes a *long* time to get up to a comfortable temp. So best burning strategy? I should know this by now, but I'm initially running my air initially to get max heat output, turning it down as low as possible while maintaining that output.
Question is, how to best maintain output from there? My thought is that I should open up the air as soon as it's more or less finished off gassing and the stove temps start to drop. Still above the coaling stage at this point. I think that this results in a shorter/less coals coaling stage, which allows me to reload faster. The whole rearranging coals/putting a split on there thing might work somewhat, but keeping the door open long enough to rearrange coals cools it down significantly, and IMO doesn't get rid of the coals as quickly.

Burn dry pine. Faster burning faster coaling and less ash. But it’s more work to reload every 3-4 hours. Pack it tight as hot reloads can really take off fast and a less exposed surface area helps keep it under control. Use a fan on the stove to increase convection. Run the stove as hot as you safely can.

Maybe you can just crack the door a smidge to burn down coals faster? At the end of the day there is a maximum output a stove has.

 

[kborndale]

What stove? What type of chimney and height? What's the moisture content of your wood? How big an area are you trying to heat? We can't help much without knowing these things.

 

[Todd]

When it’s cold and I need more heat I’ll burn half loads hotter. This helps keep the stove hot and the coals from piling up.

This is your Jotul 602? With that stove when you reach the coaling stage rake the coals forward and open the air up. It won’t take long to bring them down to reload size.

 

[nola mike]

What stove? What type of chimney and height? What's the moisture content of your wood? How big an area are you trying to heat? We can't help much without knowing these things.

Sure you can. Don't think any of that makes much difference as far as the question posed. Chimney is 20' or so, the house is 1500 sq ft but I heat it up in waves (my bedroom is still 45' atm but living room is 69' ). MC is 15%.

Burn dry pine. Faster burning faster coaling and less ash. But it’s more work to reload every 3-4 hours. Pack it tight as hot reloads can really take off fast and a less exposed surface area helps keep it under control. Use a fan on the stove to increase convection. Run the stove as hot as you safely can.

Maybe you can just crack the door a smidge to burn down coals faster? At the end of the day there is a maximum output a stove has.

Yeah, less of an issue as far as coals with pine, but obviously trade offs there as well. And I burn what I have. I usually will use pine more loosely packed for the first load to get the stove up to temp more quickly. Once the oak gets cooking, or on a hot stove, it burns as hot/hotter for longer. Cracking the door will burn the coals faster certainly. As far as maximum output, agreed. This stove (the drolet) is an insert with a fan. Separate question is does it matter what fan speed you're running at (I'd say negligible if anything).

Perhaps I should rephrase: does opening the air earlier (before actual coaling) have any downsides as far as heat output? Does it make sense that I could get more ultimate heat and shorter time to reload doing that?

 

[nola mike]

When it’s cold and I need more heat I’ll burn half loads hotter. This helps keep the stove hot and the coals from piling up.

This is your Jotul 602? With that stove when you reach the coaling stage rake the coals forward and open the air up. It won’t take long to bring them down to reload size.

Not so much the 602. That thing is a blast furnace with the air open and much less tolerant of air changes in general. Takes 10 minutes to go from full coals to needing kindling again with the air open LOL. This year though I've been turning the air down much earlier and going more by the looks of the flames than the temps, which as you I'm sure know vary wildly depending on where they're measured and take a while to catch up to what's actually happening. A cooktop temp of 700' is only smoldering. Doing this I think leads to a longer off-gassing phase, and the bottom of the stove heats more, so I think more ultimate heat output/less out the chimney. I actually haven't turned on the heat during this cold snap in a 2500 sq ft house (although upstairs is cold ~60' and all the doors are closed). But all that's more 602 specific, although the general question is the same, and I've been trying to turn up the air earlier after off-gassing on that one as well.

 

[EbS-P]

Sure you can. Don't think any of that makes much difference as far as the question posed. Chimney is 20' or so, the house is 1500 sq ft but I heat it up in waves (my bedroom is still 45' atm but living room is 69' ). MC is 15%.


Yeah, less of an issue as far as coals with pine, but obviously trade offs there as well. And I burn what I have. I usually will use pine more loosely packed for the first load to get the stove up to temp more quickly. Once the oak gets cooking, or on a hot stove, it burns as hot/hotter for longer. Cracking the door will burn the coals faster certainly. As far as maximum output, agreed. This stove (the drolet) is an insert with a fan. Separate question is does it matter what fan speed you're running at (I'd say negligible if anything).

Perhaps I should rephrase: does opening the air earlier (before actual coaling) have any downsides as far as heat output? Does it make sense that I could get more ultimate heat and shorter time to reload doing that?

Yes crank that fan to max. I see my flue temps drop at least 50F once the fan comes on then the more air it blows the more it drops.

Are your tubes glowing? Got my 1800i glowing last night. The holes were brighter than the tube. Kinda neat to see. I wouldn’t make a habit of running every fire that hot but a dull glow when you need the heat is probably ok.

 

[EatenByLimestone]

Opening up the air allows you to convert the wood into heat faster. This doesn’t always mean more heat will go into the house as it can very easily push it up the flue. The balance point is probably different with every stove. As far as running the blower, slower speeds allow the air to warm up more since it’s in contact with the stove longer, but faster speeds will transfer more heat as the heat will move to the colder surface faster. The moving air will probably feel cooler though.

 

[EbS-P]

The moving air will probably feel cooler though.

if the STT temps are near 700 F the air is plenty hot!

 

[EatenByLimestone]

When I enter the cold cabin, I close the doors to outlying rooms and heat the main room first. Once that gets to temp, I open the side rooms up one at a time.

 

[nola mike]

Yes crank that fan to max. I see my flue temps drop at least 50F once the fan comes on then the more air it blows the more it drops.

I can't think of why that would be the case. The firebox temp shouldn't be affected I wouldn't think. But I can't measure flue temps on the insert.

Are your tubes glowing? Got my 1800i glowing last night. The holes were brighter than the tube. Kinda neat to see. I wouldn’t make a habit of running every fire that hot but a dull glow when you need the heat is probably ok.

Yeah, they routinely glow. I can for sure push both stoves to the limits if needed, which is most of the time esp if it's cold out.

Opening up the air allows you to convert the wood into heat faster. This doesn’t always mean more heat will go into the house as it can very easily push it up the flue. The balance point is probably different with every stove. As far as running the blower, slower speeds allow the air to warm up more since it’s in contact with the stove longer, but faster speeds will transfer more heat as the heat will move to the colder surface faster. The moving air will probably feel cooler though.

Exactly. Don't want to lose precious BTUs up the flue, but I'm willing to trade some efficiency for more output if need be. As far as the fan goes, that's my thinking (and easily verifiable, since on the insert I measure the temps of the outcoming air as a surrogate for STT). My only thought would be that those (marginally) higher temps behind the stove would lead to more heat transfer to the structures back there instead of into the room. The fan feels good whether it's coming out at 300' full speed or 350' on low!

if the STT temps are near 700 F the air is plenty hot!

Not on the 602. Different animal.

When I enter the cold cabin, I close the doors to outlying rooms and heat the main room first. Once that gets to temp, I open the side rooms up one at a time.

Yeah, I mentioned that above. We even have a room the kids call "the cold room".

 

[MongoMongoson]

I can't think of why that would be the case. The firebox temp shouldn't be affected I wouldn't think. But I can't measure flue temps on the insert.

This is very much the case. We monitor the flue temperatures with a thermocouple in the stove pipe about 18" above the stove top, and turning the blower on high drops the flue temperature. It is easy to observe with a sensitive temperature monitor. When my stove wants to push 700 degrees (we have high draft), the first thing I do is turn the blower on high. That will cause the flue temperature to begin dropping. The next step, if it wants to keep climbing, is to use the stove pipe damper.

I agree that the fire inside the firebox is probably not burning any cooler, at least not immediately, when the blower is turned on. The blower is pulling more BTUs from the back of the stove and the stove top, though... enough that it cools the gases leaving the stove. This can, ultimately, cool the fire in the firebox. Less heat up the stack means less draft. Less draft means less aggressive burning, and that can change the stove from being in a runaway state to a state that is controllable.

When I want max BTUs/hour, I run the blower on high. I will feed the stove more often with small loads doing hot reloads to keep the firebox temperature up. With hardwoods, this can create excessive amounts of coals in the firebox. Later, when I have a pile of coals that need to be burned down, I will rake the coals to the front in a pile and put one or two small splits EW (preferably softwood) on top of the coals, running the stove with the primary air as open as I can without overfiring.

 

[EbS-P]

I can't think of why that would be the case. The firebox temp shouldn't be affected I wouldn't think. But I can't measure flue temps on the insert.

More cfm of cold air extracting heat from the firebox. Same way blowing in soup cools it faster. The heat has to go somewhere. It goes into the air then it heats the house.

 

[nola mike]

This is very much the case. We monitor the flue temperatures with a thermocouple in the stove pipe about 18" above the stove top, and turning the blower on high drops the flue temperature. It is easy to observe with a sensitive temperature monitor. When my stove wants to push 700 degrees (we have high draft), the first thing I do is turn the blower on high. That will cause the flue temperature to begin dropping. The next step, if it wants to keep climbing, is to use the stove pipe damper.

I agree that the fire inside the firebox is probably not burning any cooler, at least not immediately, when the blower is turned on. The blower is pulling more BTUs from the back of the stove and the stove top, though... enough that it cools the gases leaving the stove. This can, ultimately, cool the fire in the firebox. Less heat up the stack means less draft. Less draft means less aggressive burning, and that can change the stove from being in a runaway state to a state that is controllable.

When I want max BTUs/hour, I run the blower on high. I will feed the stove more often with small loads doing hot reloads to keep the firebox temperature up. With hardwoods, this can create excessive amounts of coals in the firebox. Later, when I have a pile of coals that need to be burned down, I will rake the coals to the front in a pile and put one or two small splits EW (preferably softwood) on top of the coals, running the stove with the primary air as open as I can without overfiring.

If that's the case then that's a double edge sword. As your firebox cools and you're coaling, that fan would hurt you.

More cfm of cold air extracting heat from the firebox. Same way blowing in soup cools it faster. The heat has to go somewhere. It goes into the air then it heats the house.

That would be more akin to blowing on a thermos that has soup in it. I think this argument is more relevant when talking about air flow INTO the stove (and out the flue). I'm not an engineer, but I don't think it's that simple. The heat extracted from the stove is dependent on both flow and temperature differential. With the fan on low the air behind the stove is hotter, and fewer BTUs are extracted, but that air is in contact for a longer period of time. Fan on high there's a bigger temp differential but less time for it to try to equilibrate. I don't know the answer, and it's probably dependent on a number of things specific to one's setup.

 

[MongoMongoson]

If that's the case then that's a double edge sword. As your firebox cools and you're coaling, that fan would hurt you.

Not if you open the primary air or add a small load of fuel to keep BTUs up. You are asking about getting max BTUs/hr long enough to get a cold house warmed up. There is nothing passive about that with wood heat.

Run the blower on high and keep the firebox hot. That is your answer. To do that, you will need to be actively involved.

My stove is nowhere near coaling if it is running at close to 700 degrees.

 

[nola mike]

My stove is nowhere near coaling if it is running at close to 700 degrees.

I meant that by that logic you'd need to reduce the fan speed as fire progressed or else you'd further cool the fire box.

 

[stoveliker]

In the end, when one wants to cool something, a fan is used.
That means the fan helps extract BTUs from the something.
If a slower fan would do that better, one would extrapolate that to zero fan would do it best. That's not the case.

So run that fan on max, and keep the firebox as hot as possible by playing with load and combustion air.