How long is a burn time?

Why is stove top temp relevant in the definition of burn time?

precaud said:

Why is stove top temp relevant in the definition of burn time?

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Id say its what still indicates usable heat by measurement on most stoves.

On my Lopi Insert, I can argue there is only decent heat distribution when the blower is on. And on a good fire, the blower kicks "off" at 300-350 degrees, which at that point, immediately limits the amount of heat flowing into my house.

I'd say "blower kick off" temp is a pretty good estimate of the end of burn time for those of us who use inserts

My stove is small and I will run it hard to heat well over what it's suppose to heat. My house loses heat slower than the stove puts it out so yes I can heat about 2000ft with a stove rated to about 800 but it takes about 6hrs to even out. Once it's up to temp, the house that is, I can maintain it rather easily.
When it's 20-30f outside I need stove temps of above 425 to add heat
350 will maintain
<300 the house starts to cool down
I let it run down to 250 so I'm not loading so often
Small firebox so 3-4hr is all I get :-S

PE t-5 should fix my problem next year

I should add the house is a ranch in the shape of an "L". Added 12" insulation to the attic now have about 20" and insulated the box plate from the basement, walls are good, new front door, and replaced all old windows

stove top temp has little to do with it for me, it all depends on what I see in the coal bed, I dont want to have to "start" the fire over, so my new burn overlaps the old coals by a good length of time.

I said 250, but my definition is only partly temperature related. I figure if I can still crank it back up easily with small splits, but no paper or kindling, then it has not yet reached the end of its burn. For me, where this seems to be just possible corresponds to a 200-300 stovetop, and is in the 8-10 hour window if I use a full load of dry hardwood.

I went with 250 as that is where I look to make the load/don't load decision for the day - if I'm going to keep burning for the day I go ahead and load up again, if I expect to let it go down to coals that have to be piled up or otherwise adjusted/thought about before piling splits on top then I let it go. Mind you it does give me several hours to make up my mind and change it... but 200-250 is the range. Being that 250 is the magic cat light-off point plays a part in this of course.

If one is trying to come up with some sort of academic "how long can you go from load to re-load" definition of load time then I agree, stove top temp has nothing to do with it. I have coals this morning that are more than enough to start up again and stove top is somewhere around 100, but I certainly don't consider the heat being put out as useful and I would be seriously annoyed if the mfgr counted the last few hours as part of the 'burn time' when selling the stove!

PINEBURNER said:

stove top temp has little to do with it for me, it all depends on what I see in the coal bed, I dont want to have to "start" the fire over, so my new burn overlaps the old coals by a good length of time.

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That was my point too. Since wood stoves require so much user interaction, "coals in the bed" is a much more relevant metric to measure burn time than temps on the top plate.

I also would say it has more to do with the coal bed than the stove temp. As BB mentioned, stove construction and mass can greatly effect how long a stove remains warm, despite the condition (or lack of) a fire.

Wet1 said:

I also would say it has more to do with the coal bed than the stove temp. As BB mentioned, stove construction and mass can greatly effect how long a stove remains warm, despite the condition (or lack of) a fire.

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And there, in my opinion, we get to the heart of the question. What is the definition of the term "burn time" anyway? Is it the length of time that you can expect useful heat from the stove (let's hold the question on defining useful heat for a few moments), or is it the time you can go from load until re-load without having to re-light the stove using a match (or is it tinder, or kindling, or just placing splits directly on the coal bed)? At any rate, just agreeing on this main two-way split would go a long way in parsing the definition in my opinion.

I can say that when I was first shopping for a stove (total noob, didn't know a thing hardly) and I read "burn time" my idea was that it meant useful heat. Yup, I was a marketing fool - read specs that had BTU output ranges next to burn time and I put the two together and figured I'd get that BTU output for their rated burn time. I still wonder what exactly a manufacture's definition of burn time is.

Anyway - if the purpose of this thread is to come up with a consensus definition of the term I'm all for it - should make for some interesting discussion. Frankly I don't care what the final outcome is, but it sure would be nice to agree to a term for each - i.e. "the time from a full load burning until it crosses below xxx degrees surface temperature is called NNN time", "The time from a full load burning until unable to start a new load going again by simply placing new splits on top of the coals expecting splits to be burning by time door is closed is called YYY time", "The time from a full load burning until the last coals are out and you can't coax a fire to start without using a match/lighter is called zzz time". I expect that each of these is being called "burn time" by some folks at different times - rather makes comparisons somewhat meaningless eh?

Stove temp is OK to monitor, but it's really just an academic exercise. I don't "really" care what the stove temp is, I care what the room/house temp is. The whole point of burning wood is to heat the house, not the stove. Sort of like driving a car and watching the coolant temp gauge - though I keep an eye on the temp, and wish it to stay in a certain range, I'm really driving to get from point to point, not to heat the coolant.

Along that line, I consider burn time to be how long can I go before I need to reload the stove to keep warm in the house. If a guy had a small stove in a big, uninsulated house, being able to rekindle a fire from coals after 12 hours is of little consequence if he's been freezing for the last 6 hours. Of course, this takes in a lot of variables of the stove, house, wood, weather, personal comfort, etc. but would seem to make the most sense. The downside is, burn time changes constantly - even for the same stove in the same house!

The definition of burn time should relate to the appliance, and not where it is installed and how it performs there. This is the first I've heard of a suggestion to use stove top temps to measure it. It's not a good choice. Stoves that have pre-heating air channels across the top will fair poorly by this measure.

IMO, there are too many variables for this to be precisely and fairly measured and then compared between stoves. The only realistic measure will relate to the time between the start of a load and when sufficient coals remain to ignite a new charge. But even that is going to be influenced by wood species, moisture content, piece size, etc.

The most reliable thing I have seen is: the more control the user has of the air supply (i.e. being able to shut ALL of them if desired), the longer one can extend the burn time of any stove.

350+ when its cold, 200 when its not or we are getting good solar gain. Not sure the relight criteria works, 3 little coals will ignite a load of pine.

I think the "burn time" is over when I no longer have wood in the firebox, even if there are still hot coals. However, I feel that my stove is still "heating" as long as it's temperature is above the temperature of the surrounding room.

Interesting arguments presented. Although I have to agree that there is great variability, I don't think that all of the possible definitions of burn time are entirely worthless. Certainly I'm sure folks will agree that a larger firebox in general will allow for a longer burn time (no matter if we are talking useful heat or time to coals to be re-lit). Someone looking to buy a new stove will certainly be interested in this relative information. Quantifying this in some way to set expectations is helpful as well. I do expect that the answer will end up being a range - not a solid number.

Likewise, I would expect that an EPA stove will give a longer CLEAN burn time than a pre-epa stove (although I'm sure someone will jump in with exceptions) but this is a generalization - again, the question here is one of quantifying and establishing a comparable number so we can perhaps relate our experiences. Using a fair set of definitions will allow those who wish to report results for their setup a way of using a common language to do so.

What anyone does with the data is up to them. How well individuals will actually gather and report on the data (how honest they will be with themselves while building the data sets and with us when reporting) remains to be seen - certainly individual bias exists and will skew the metrics. But I don't think that establishing common definitions will be a waste of time nor do I believe that it would be useless to see what results can be gathered. I for one would like to see how differently common stove models perform in different installations - and also with different fuels (hard/soft wood for example) and in different weather conditions. True, we'll end up with an academic definition of a term that may not directly relate to anything someone should run out and use as a deciding factor when making a purchase, but it may help guide someone who is either buying or perhaps maintaining their stove (i.e. perhaps if one were to monitor such things it could be an indication of a Cat needing to be cleaned or replaced? Chimney cap being plugged?) - Yup, I'm the type that keeps track of my car's MPG on each fill-up in case it changes dramatically.

Slow1 said:

(i.e. perhaps if one were to monitor such things it could be an indication of a Cat needing to be cleaned or replaced? Chimney cap being plugged?)

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Now you're talkin. Remote monitoring of stove temp, cat temp, weight of fuel remaining in firebox and remote control of the thermostat and fans. If they can put scales on the buckets of payloaders at the quarry and control a combine via satellite, controlling a stove should be a snap.

I get 16 hour burn times and I'm hungrier than you.

We do have some dealers as members here, so please tell us what the manufacturers use to measure and define burn time.

For me if something is burning even coals and the fire does not need to be restarted with paper, firestarter, etc it is burn time. It may not be useful for heating the house but it is burning. These vary by every load of wood, outside temp, wind, draft, home insulation, windows, we can go on and on with the variables. The useful heat measurement is not measurable as a standard because of all of the variables and user preference to temp of house.