How do you measure burn time?

[Bomann]

Hi everyone,

Just a technical question.
How to you exactly measure or define burn time?
Let us say the timing begins when you reload the stove but when is it considered to end?
The point when the burning wood stops burning with big flames and you have a big load of glowing embers?
Or the point when the embers "calm down" a bit more and you have a nice coal bed?
Or is the end of the burn time the point when the fire goes out completely and ther is only ash remainig (maybe some glowing coals) and an almost cold stove?
I just was wondering about this as i read what burn times others reach...
Considered the above options my burn times can reach from 50 minutes to several hours depending on how I define it...

Thank you for your thoughts
Cheers,
Bo

 

[firefighterjake]

Well as noted there can be a lot of definitions for "burn time" since there really isn't any technical, hard and fast definition.

For me I guess I would define burn time from the moment the woodstove is brought up to temp so it begins producing heat until it reaches the late coaling stage when it is no longer radiating any meaningful heat (ie it may be warm, but not hot enough to really heat the home.) Of course there are a lot of variables and this is entirely a subjective view/definition.

 

[Handsonautotech]

I would think it is considered to be after the hot embers staft to die off. I can not get anything to burn with flame for longer then three hours.

 

[begreen]

Burn time is often just a marketing term. Based on some claims it's from the second a match is lit to the moment the last spark is present in the firebox. Not too helpful. More helpful is like Jake stated, the period of meaningful heat. That depends on the house's heat loss and outside temp but it usually is something like from when the stove top hits 250ºF to the time when it returns back to that temp and the stove needs reloading. This topic comes up several times a year. If you search on burntime several threads will show up on this topic.

 

[Sprinter]

1. Until the stove is stone cold.
2. Until the the stove top is 200F.
3. Until the house is cold.
4. Until the coals go dark.
5. Until you can start a new load with the remaining coals.
6 Make up your own definition.
7. Six hours for a non-cat, forever for a cat.
8.. Until the dog or cat gets up and leaves.

Take your pick.

Feel free to add.

 

[yooper08]

I like this definition:
Burn cycle time is the period between loading wood on a coal bed and the consumption of that wood back to a coal bed of the same size.

 

[Tech Guru]

yeah, there is no real set definition for this. Although your old EPA hang tags would give a much lower BTU readings than your typical Sales or Marketing literature would give as MAX BTU's, and this one is more explainable, and in a way, relates to burn time:

The EPA test was done from a cold start up until a cold finish (you had to be able to put your hand on the coals). SO one fire cycle. That's It. NO more.

The Max BTU's test was typically done by the manufacturer (not necessarily in an EPA or certified test lab, but usually) operating a stove in a manner similar to a user would as a main source of heat - with a 4 to 6 load cycle where the stove was brought up from a cold start once, and then reloaded while still hot enough to start your next load from embers. hence a stove that might give around 25 or 30M Btu's as it's high level on the BTU hang tag could have another number listed of MAximum 50,000 BTU's.

It is funny to think that a stove of the same size firebox as another, with a very similar secondary burn method could have one manufacturer list 45m or 50M Maximum, and another 70M, and even one more at 80M. Unless that firebox is significantly larger or the secondary burn drastically different, those 'real world' numbers would all be right about the same (on the same chimney set up with same wood species).

As a former Manufacturer, I would consider burn time to be whenever the stove was emitting heat, so as detailed above by firefighterjake and more. So an active, heat emitting bed of coals counts.

 

[begreen]

The EPA test results are based on a fixed fuel load and air settings. The EPA testing results between stoves are comparable. Maximum output testing is not tightly documented so it's hard to know what the fuel source is, what species of wood was used and what volume of wood, etc.. Very few people are going to run a stove at maximum output so this number is less meaningful.

 

[Sprinter]

And so it goes...

Welcome to the forum, BTW, Bo. Your question is a good one. Unfortunately, there is no good answer in return. All the above answers have merit, but the problem is that without an accepted, easy to test definition for the consumer, comparisons are difficult and may always be.

As you've discovered, there is no accepted definition, and so many variables based on fuel, technique, etc., that pursuing it is rather pointless IMO. I guarantee that 20 PE Super27 owners (just for example) will report 20 different burn times depending on all those variables, and probably will be different day-to-day anyway. Bottom line is that it is completely meaningless in the real world if you want quantitative figures.

Even within the realm of catalytic stoves, objective, quantitative, useful figures are just as elusive, although it's pretty much accepted that cat stoves will generally provide useful heat longer than non-cat stoves, but even that is hard to quantify and still depends on proper operation as with any stove.

Now, that's not to say that some stoves aren't better than others within the same size and type due mostly to efficiency, but the differences are slight and proper use and fuel quality will trump any slight differences in efficiency.

Another thing to keep in mind is that the largest stoves (say >3 cf) will offer longer burn times than small stoves, obviously, but you would need to decide if those are the right size for your situation, and even that only applies when you fill the stove to capacity.

 

[jzampieron]

I can relate my highly scientific method:
1. Find small number of coals in stove after previous overnight burn.
2. Add splits and logs until "Engage the Cat!" and then "Choke off the air"
3. Enjoy the glow for ~8-12 hours.

Basically, I'm timing how long a nice slow burn lasts once I'm at heating temp and I don't have to think about it anymore.

Heating temp varies on how cold it is outside, but I run anywhere from ~300 deg F to 650 deg F.

I honestly don't care all that much about burn times as long as its at least 8 hours. I can sleep, go to work, etc and reload without having to rekindle or worry about the furnace running, which we keep set at 65.

Wood variety mix makes a difference. A nice load of maple or oak gives more coals left in the morning vs pine and birch.

 

[Bomann]

Thank you all for all the detailed and professional thoughts, and also for the less scientifc ones

The definitions of firefighterjake and yooper08 are the closest to what I understand under burn time.

How about that?
Burn time is the exact amount of time that passes from the moment you start the stopwatch to the moment you stop it when watching a fire in any burn phase..

I really just popped the question out of curiosity to be able to compare my sotve's performance, thinking there was a commonly accepted way or definition , but reading your answers made me think about it a lot and I realised that "burn TIME" is really just the tip of the iceberg and is really defined by a million factors.

I don't say I couldn't sleep (here it is now 10:30 AM), but I thought a lot about how the performance or capabilities of a stove could be defined the most precisely based on objective parameters but (of course) I did not find the holy grail.

Maybe the only factor that is fixed and is the same every time is the size of the firebox, which sets the limits and capabilities of the stove but again is just one parameter of the many.

I myself do not care much about burn time. I mean it is not the most important. Of course it is nice to have the freedom to leave the fire alone for several hours and not having to reload it frequently but this is just a question of convenience.
What counts in the end, is that our stove is able to heat our home as we thought/expected it would and so far we are OK with the amount of wood needed for that. I hope I can report the sasme in May ( Our new stove was just installed 2 weeks ago, and temperatures just started to drop)

Just as curiosity:
Where I live (Hungary,Central Europe) burn time is not an issue at all. (A more common question is: how much wood do you burn a season?) Main reason for that is maybe that the traditional source for woodheat here are tile stoves. You pack the firebox full, burn the wood intensely, it goes down in 1-1,5 hours, and you have a warm stove for 8-12-16-24 hours depending on the size of the stove and a few other things as usual.
Of course there are many other options getting popular from cheap DIY store stoves to modern fireplaces connected to the central heating but this is a different story


Bo

 

[CheapBassTurd]

The box on the pigbelly is like a 27 inch deep barrel on it's side.
Single controllable air inlet front, chimney rear. With a good coalbed
scooped forward we can do pretty good. (7 hot/2 warm hrs.)
Small row of pine over coals, scrounge-mix of mediums and hards as
high as 2/3 of the box. (Std n/s, e/w mix.) The resulting hotbed left in
the back 1/3 leaves residual heat a few hours after burn too as a small
bonus. The furnace turned on twice on it's own from the time it's been
in service. I think we set it at 64 for the kids and dogs.

 

[yooper08]

To compare your stove, here's a very general indication based on firebox volume. Granted, this depends on a lot of other things, mostly how much air you allow and wood species, but these are essentially theoretical maximums.

• <1.5 cuft: 3-5 hours
• 1.5-2.0: 5-6
• 2.0-2.5: 6-8
• 2.5-3.0: 8-9
• >3.0: 9-10

 

[Bomann]

To compare your stove, here's a very general indication based on firebox volume. Granted, this depends on a lot of other things, mostly how much air you allow and wood species, but these are essentially theoretical maximums.

• <1.5 cuft: 3-5 hours
• 1.5-2.0: 5-6
• 2.0-2.5: 6-8
• 2.5-3.0: 8-9
• >3.0: 9-10

Thanks!
Being a European I think in meters, ccm-s and Celsius degrees so I am pretty much lost when you refer to inches, cubic feet, Farenheits and cords :D
But google is my friend, I'll do the maths.

But without knowing the exact measures of my firebox I am quite sure my stove falls in the first category as it is a (by U.S. measures) small stove, a Jotul F3 TD.

 

[begreen]

These times will vary with how cold it is outside and how hard the stove is being pushed. In milder weather our stove's burn time is 10-12hrs, but in much colder weather it could be 8hrs. The burntime may also vary between an EPA and non-EPA version of the stove due to the greater efficiency of the EPA stove.

 

[mellow]

Burn times will also vary with firebox size when alien technology is used.

 

[begreen]

True even for terrestrial burners.

 

[Sprinter]

Burn times will also vary with firebox size when alien technology is used.

Those anti-matter flux generators make a big difference. Apparently, BK has borrowed from some aliens a proprietary method of gathering and introducing electrons and positrons from the firewood, thus emitting 511 kvA photons in opposite directions which has the effect of converting their energy into infrared lambda photons at opposing ends of the stove, thus providing double the heat emission from the stove. That also has the effect of doubling the burn time.

 

[prezes13]

I have an insert with an automatic fan, comes on when stove reaches certain temp and shuts off when it cools down to a certain temp. Time from the moment the fan start to the moment it stops is a burn time for me.