Discussion: hotter fire or slow burn?

[Mr. Kelly]

Hi all…

I saw a video recently online with a guy who suggested running your stoves hotter throughout the day in order to have a more stable temperature environment, and for me, more importantly, to use less wood.

This kind of struck me as being counterintuitive, since I have always thought that if I get my stove burning as low as I can (that would be practical), I would go through wood less quickly…

His experience has been that when he burns hotter, it heats the house up more robustly, and it takes a longer time for the house to cool off, therefore he has to have fewer fires during the day… By contrast, my fires result in a cooler house with more dynamic temperature changes, from what it seems.

What have your experiences told you about this?

I am trying it now, but yet to have any new enlightenment.

 

[bholler]

Hi all…

I saw a video recently online with a guy who suggested running your stoves hotter throughout the day in order to have a more stable temperature environment, and for me, more importantly, to use less wood.

This kind of struck me as being counterintuitive, since I have always thought that if I get my stove burning as low as I can (that would be practical), I would go through wood less quickly…

His experience has been that when he burns hotter, it heats the house up more robustly, and it takes a longer time for the house to cool off, therefore he has to have fewer fires during the day… By contrast, my fires result in a cooler house with more dynamic temperature changes, from what it seems.

What have your experiences told you about this?

I am trying it now, but yet to have any new enlightenment.

It really depends upon the stove, the chimney,
the house, and the fuel. In some cases quick hot fired are better others work well low and slow

 

[Highbeam]

His experience has been that when he burns hotter, it heats the house up more robustly, and it takes a longer time for the house to cool off, therefore he has to have fewer fires during the day… By contrast, my fires result in a cooler house with more dynamic temperature changes, from what it seems.

That person was just overheating his house and then letting it cool for a larger swing in temperature and probably more wood consumption than if he had just held the house temperature constant for the same period. Using his home's mass as a sort of thermal storage battery since his stove is apparently not capable of burning slowly enough to produce heat at the same rate that his house loses it. It's a common problem with an oversized stove.

Overheating the house can have a useful application like if you have an expected absence from the home and want to "charge it up" before leaving to minimize temperature drop.

 

[stoveliker]

His experience has been that when he burns hotter, it heats the house up more robustly, and it takes a longer time for the house to cool off,

That (longer cool down) is only true if the home is heated up higher. And if he heats up the home to a higher temperature, he'll have used more wood in that timeframe than if he'd heated the home to a lower temperature in that same timeframe.

He'll have fewer fires (or better, he'll burn less many hours per day), but those fires (hours) will consume more wood per hour. That will likely be a wash.

therefore he has to have fewer fires during the day… By contrast, my fires result in a cooler house with more dynamic temperature changes, from what it seems.

What have your experiences told you about this?

I am trying it now, but yet to have any new enlightenment.

I suggest that the effects of this will be mostly dependent on the efficiency of the stove; does it stay the same when burning higher? If so, I don't think you'll see a meaningful difference.

What you will see, is a varying degree of comfort (too hot, okay, too cold) versus a constant "okay".

 

[EbS-P]

Heat loss rate is completely independent of the stove and only depends on the house, and the outside conditions.

Arguments could be made that a smoldering fire is inefficient as smoke is unburdened fuel. So let’s assume both hot and slow fires are clean burning with nearly the same efficiency. If your house looses xxxxx btus it doesn’t matter if the fire is hot or slow the same number of btus needs to be replaced either way.

Now each stove probably has some efficiency vs burn rate curve/peak.

I’m skeptical

 

[Mr. Kelly]

Well… Interesting thoughts, thank you.

Here’s where this question came from: I have a very inefficient system in my house. I have a PE Summit (which one would think would blast you out of a small house, which mine is), but it’s very inefficiently set up… It has multiple twists in the roughly 6 foot pipe that leads horizontally out to a T that runs outside of my house and up about 15 feet.

It doesn’t draft well at all. Most of the time, I have to leave the door open when I first load the thing, particularly after long burns, just to get the thing going.

The stove seems to run with two levels of damper… Either off or on. If I don’t turn the damper all the way off, the thing will burn like crazy… But if I just put in the tiniest bit of air by moving the damper to the left, it starts burning hotter than I would like it to. There seems to be no sweet spot.

Most of the time, After I get the fire burning satisfactorily, I run the thing mostly off… but it’s a very low burn, sometimes smoldering… And I can’t easily get my house temperature into a satisfactory range. Conversely, I just open it up a bit, and it burns way faster than I would like it to…

So… I’ve been letting this thing run much hotter for the last 24 hours, or so, and it is still inconclusive… It doesn’t feel like I’ve been using any more wood, but my house seems definitely more consistently warm. So, in that regard, it seems like running it a bit hotter may pay off, for reasons I can’t yet quite explain.

I’ll certainly be thinking about some of your thoughts to try to come to some conclusions…

 

[bholler]

Well… Interesting thoughts, thank you.

Here’s where this question came from: I have a very inefficient system in my house. I have a PE Summit (which one would think would blast you out of a small house, which mine is), but it’s very inefficiently set up… It has multiple twists in the roughly 6 foot pipe that leads horizontally out to a T that runs outside of my house and up about 15 feet.

It doesn’t draft well at all. Most of the time, I have to leave the door open when I first load the thing, particularly after long burns, just to get the thing going.

The stove seems to run with two levels of damper… Either off or on. If I don’t turn the damper all the way off, the thing will burn like crazy… But if I just put in the tiniest bit of air by moving the damper to the left, it starts burning hotter than I would like it to. There seems to be no sweet spot.

Most of the time, After I get the fire burning satisfactorily, I run the thing mostly off… but it’s a very low burn, sometimes smoldering… And I can’t easily get my house temperature into a satisfactory range. Conversely, I just open it up a bit, and it burns way faster than I would like it to…

So… I’ve been letting this thing run much hotter for the last 24 hours, or so, and it is still inconclusive… It doesn’t feel like I’ve been using any more wood, but my house seems definitely more consistently warm. So, in that regard, it seems like running it a bit hotter may pay off, for reasons I can’t yet quite explain.

I’ll certainly be thinking about some of your thoughts to try to come to some conclusions…

You need to fix the setup and get the stove working properly before worrying about anything else

 

[Highbeam]

Heat loss rate is completely independent of the stove and only depends on the house, and the outside conditions.

I do agree that the rate of heat loss in independent of the stove but I believe that heat loss from the home is greater as the temperature of the home gets higher than the outside temperature which is very relevant to the discussion. In other words, a house at 80 degrees inside is losing more heat to the outdoors than if the house was 60. That differential drives the flow of heat from inside to outside and is why when it is 70 inside and outside, there is no heat loss.

The summit has a great reputation. As a noncat it likes to run hot but you should have some level of control between max and min output. Being in a small home, that large stove when running even reasonably as designed will feel very hot. I bet your quenching the secondary combustion when on low and then using secondary combustion when hot so it feels very on/off.

 

[TomMcDonald]

I'm attaching this picture as a rough reference regarding amount of wood burned on high vs low (from an Australian made wood stove) during compliance testing.
You'll see that you burn almost 3x as much wood on high as you do on low but for only a bit more than twice the heat output (this may differ from Cat stoves, etc.).
Would seem to make more sense to me to burn slowly and keep the fire going rather than have multiple fires.
Tom.

 

[Poindexter]

I go through this every year, my answer is it depends on the weather.

I typically light up in late August when overnight lows are dropping into the low 40s burning a small load on high to take the chill off the house before bed. I change my burn schedule through all the variations down to overnight lows around -50dF with daytime highs around -42dF when my stove is swallowing three full loads daily.

I find my house "degree loss per hour" is more or less zero around +40dF, and more or less linear down to about -20dF where I am losing about 2 degrees (F) per hour. At -35dF the bottom falls out, I have crossed the exponential knee, and my degrees lost per hour increases rapidly with small changes to colder outdoor temperatures. My local finding is the higher the difference between indoor and outdoor temps, the higher degree loss per hour I see.

I am in agreement with previous posters the OPs chimney pipe arrangement is suboptimal. I would look for meaningful gains replacing the indoor pipe with 2 of 45 degree elbow and 3 pieces of straight pipe, one of which will have to be telescopic.

At the end of the heating season, wood burned in the stove is BTUs in the envelope that weren't made with more expensive oil or electricity. In some circumstances it might make sense to let the house cool off during the day while no one is home, but the "catch up" expense of increased BTU demand to heat the house back up should not be overlooked and depends somewhat on the degree loss per hour of the insulation envelope at whatever indoor and outdoor temperatures.

I personally choose a setting on morning reloads that will give me a decent bed of coals to reload on when I get home in the evening.

 

[Prometeo]

Hi all…

I saw a video recently online with a guy who suggested running your stoves hotter throughout the day in order to have a more stable temperature environment, and for me, more importantly, to use less wood.

This kind of struck me as being counterintuitive, since I have always thought that if I get my stove burning as low as I can (that would be practical), I would go through wood less quickly…

His experience has been that when he burns hotter, it heats the house up more robustly, and it takes a longer time for the house to cool off, therefore he has to have fewer fires during the day… By contrast, my fires result in a cooler house with more dynamic temperature changes, from what it seems.

What have your experiences told you about this?

I am trying it now, but yet to have any new enlightenment.

With a radiant stove, it's true in my case, if I burn very hot, the heat circulates more, in all rooms, if instead I go slow, heat does not move easily to other rooms, while in convective stoves maybe it's different

 

[peakbagger]

The person who invented the world most efficient "stove" (actually a boiler) for many years running, Dr Richard Hill designed the U Maine wood boiler to burn as hot as possible for the shortest period of time. He also came up with concept of separate thermal storage. As long as there is enough heat exchanger area downstream of the "fireball" the hotter the better for residential. Once combustion moves into the commercial category, there is a concern about thermal NOx generation so then staged combustion comes into play with a long combustion zone and staged combustion air.

He was also a fan or owning two stoves, a small one that could be fully loaded for shoulder season and a larger one for the coldest time of the year that also would be run at or near full load.

 

[stoveliker]

With a radiant stove, it's true in my case, if I burn very hot, the heat circulates more, in all rooms, if instead I go slow, heat does not move easily to other rooms, while in convective stoves maybe it's different

A very hot burn will heat the room up more, allowing for more energy flow to other rooms because of the larger temperature gradient.

However, that also hold for the energy flow to the outside of your home...

 

[Prometeo]

A very hot burn will heat the room up more, allowing for more energy flow to other rooms because of the larger temperature gradient.

However, that also hold for the energy flow to the outside of your home...

I agree. However a convective stove, heating the air directly should keep moving air longer,
without heating nearby objects, as a radiant does

 

[gthomas785]

Smoldering wastes wood, that's for sure. Every particle of smoke is unburned fuel.
On the other hand, introducing excess combustion air will increase flue velocity (and mass flow, and temperature), wasting energy that way. So it's a balance. If you can slow down the burn to a controllable rate without creating smoke, which is what most modern stoves are designed to do, then you'll get the best efficiency.

 

[Prometeo]

Smoldering wastes wood, that's for sure. Every particle of smoke is unburned fuel.
On the other hand, introducing excess combustion air will increase flue velocity (and mass flow, and temperature), wasting energy that way. So it's a balance. If you can slow down the burn to a controllable rate without creating smoke, which is what most modern stoves are designed to do, then you'll get the best efficiency.

yes and in fact normal stoves are more efficient when they burn strongly, so maybe that guy's reasoning makes sense

 

[stoveliker]

I suspect there are some language issues here. What is normal, what is meant by efficient.

But whatever "normal" is for you, efficiency does not always improve when burning "stronger"; in both tube stoves and cat stoves, residence time matters for combustion efficiency.

Heat transfer from the stove to the room is another thing.

 

[Prometeo]

I suspect there are some language issues here. What is normal, what is meant by efficient.

But whatever "normal" is for you, efficiency does not always improve when burning "stronger"; in both tube stoves and cat stoves, residence time matters for combustion efficiency.

Heat transfer from the stove to the room is another thing.

Yes there are inaccurate words, thanks for pointing this out, I want improve!
By normal stoves I mean recent stoves, without cat.
These no-cat stoves have better efficiency when burning hotter, and this coincides with the air all open, and full firebox, if the draft is about as the manual says. I think all open air It is proportionate to firebox capacity, stove technology, etc. If we could have a 48 hours burn / efficiency 100 we won't heat a house anyway. In my little experience, my stove always works better with air all open, even when there are only coals, I can extract useful heat, for my masonry house, which has a lot of dispersion.
After that I can stay a few hours without recharging. While when I used a barometric damper, heat was little, ridiculous temperatures!

 

[bigealta]

My jotul f400 kicks out much more heat when there are robust secondary flames. When choked down enough, the secondairies are either weak or off. And with that the stove is much cooler. I don't find the splits last that much longer when the stove is overly choked down, but i do find the heating is much deminished. Unburnt fuel is a waste. I'd rather err on the side of letting to much heat escape the chimney than let cool unburnt fuel out of it.

 

[VintageGal]

For all the thought that went into these EPA miracles, the quality of their air control levers, dampers or whatever they're called are very primitive. I'd like to see more robust quality and craftsmanship in the air lever controls.

I doubt I used the correct nomenclature lol

 

[stoveliker]

I'm not sure what levers you have, what stove you have.
But most of them are rather simple, and by necessity therefore rather robust (as compared to e.g. the air supply on "quality engineered pellet stoves"...!).

My stove's air control is already quite sophisticated, but still incredibly (as in it's almost hard to believe one can make a system that good with such stupidly simple technology) simple...

 

[bigealta]

For all the thought that went into these EPA miracles, the quality of their air control levers, dampers or whatever they're called are very primitive. I'd like to see more robust quality and craftsmanship in the air lever controls.

I doubt I used the correct nomenclature lol

Although my Jotul f400 is not a perfect stove, i have to say the build quality is very good on the one i have. If i vacuumed it out and did a detailed wipe down with a damp cloth it would look and act almost like brand new. Even the gaskets are all still good after years of use.

 

[bigealta]

And if i did not let water drip on the back of my jotul 3, it too would still be in excellent condition fter almost 20 years of heavy use. (but that is a pre epa stove). But the 3 and the f400 and f 500 are basically built pretty much with the same high quality, at least until a couple years ago.

 

[VintageGal]

I'm not sure what levers you have, what stove you have.
But most of them are rather simple, and by necessity therefore rather robust (as compared to e.g. the air supply on "quality engineered pellet stoves"...!).

My stove's air control is already quite sophisticated, but still incredibly (as in it's almost hard to believe one can make a system that good with such stupidly simple technology) simple...

I'm not sure what levers you have, what stove you have.
But most of them are rather simple, and by necessity therefore rather robust (as compared to e.g. the air supply on "quality engineered pellet stoves"...!).

My stove's air control is already quite sophisticated, but still incredibly (as in it's almost hard to believe one can make a system that good with such stupidly simple technology) simple...

 

[bholler]

Yes there are inaccurate words, thanks for pointing this out, I want improve!
By normal stoves I mean recent stoves, without cat.
These no-cat stoves have better efficiency when burning hotter, and this coincides with the air all open, and full firebox, if the draft is about as the manual says. I think all open air It is proportionate to firebox capacity, stove technology, etc. If we could have a 48 hours burn / efficiency 100 we won't heat a house anyway. In my little experience, my stove always works better with air all open, even when there are only coals, I can extract useful heat, for my masonry house, which has a lot of dispersion.
After that I can stay a few hours without recharging. While when I used a barometric damper, heat was little, ridiculous temperatures!

Non cat stoves (atleast the ones we have in the states) absolutely do not burn most efficiently with the air all the way open. Doing that wastes a large percentage of heat out the chimney.