Are BTU figures mainly a bunch of lies?

I initially posted this within a different current subject topic in response to forum member rbergs contention that all BTU figures are lies. Now I feel this subject deserves it's own thread. Here is a repeat of what I posted:

At 70% efficiency 100,000 BTU's of output for one hour would require the consumption of roughly 11.5 pounds of coal. That's about 276 pounds of coal burned per day.

50 pounds of coal burned per day is yielding about 18,000 usable (output) BTU's per hour.

I wonder if a coal stove would survive one full day of non-stop 100,000 BTU's per hour output. I could imagine it glowing.

I suspect that most stoves run most often at 15% (or less) of their manufacturers rated output.

lsayre wrote:
I wonder if a coal stove would survive one full day of non-stop 100,000 BTU's per hour output.

Yes..

Flyer5 wrote:

lsayre wrote:
I wonder if a coal stove would survive one full day of non-stop 100,000 BTU's per hour output.

Yes..

I should have known that a 'Leisure Line' stove could do this. Is that one of the UL certification tests? Would it glow (outwardly)?

Of course it would continue at that output. Think your AHS would crap out? I KNOW that it won't. Try an AA 260 cranked....if you can keep a load on it, they will produce the fire. AA, EFM, Keystoker, GJ, Van Wert, Losch.....all of them. This in not Chinese junk, this equipment is the real deal. I never understand your questioning everything......WTF!!!!! Do you not understand anything mechanical? The formulas are easy to enter data into....that produces a result.....a verified result.


GRRRRRRRRRRRRRRRRRRRRRRRRRRRR eek2:

Whoa! This thread was posed as a question, and it was initiated in response to a claim made someone else no less. If you actually read my post the only thing I'm asking about is if a stove could survive longer term at its full rated output and if it would glow in doing so. At least boilers have their firebox mostly surrounded by water, so I doubt they would glow.

I also suspect that stoves run mainly at around 15% or less of rated output. I hope that doesn't cause everyone to go into fits of rage and frenzy.

I'm rolling on the floor.....and no, the rating are realistic. The fuel source could vary a bit......and the boiler restrictions could change (fly-ash build-up,on plates and tubes... surfaces)
This is not like the three biggest lies...which end in : 'and the check is in the mail!'

When I was about 9 or 10 years old the TV repair man was working on our set, and I was in there asking question after question. My Mom chided me but my Aunt Mary (who was visiting) spoke up boldly in my defense and said "How will he ever learn if he doesn't ask questions?". I took that as a positive sign that asking questions was a good thing. Perhaps in retrospect I should have listened to Mom?

Mom was on to something big......unfortunately.....

lsayre wrote:Whoa! This thread was posed as a question, and it was initiated in response to a claim made someone else no less. If you actually read my post the only thing I'm asking about is if a stove could survive longer term at its full rated output and if it would glow in doing so. At least boilers have their firebox mostly surrounded by water, so I doubt they would glow.

I also suspect that stoves run mainly at around 15% or less of rated output. I hope that doesn't cause everyone to go into fits of rage and frenzy.

I agree completely. Most ratings are pure fantasy, perhaps sustainable in one test firing and unrelated to day to day use. If you measure the heat emitting surface it is not hard to calculate the necessary temperature that surface would have to be to reach the claimed figure.

If a stove has a good fan system to 'wash' the heat off of the stove body, then it probably will NOT be glowing red, and if any part is nearing red-heat temperatures, it would be the firebricks around the fire..

Even the antique stoves with a firepot exposed on the outside to the room being heated, rarely glow red, and if the firepot has a refractory lining, the pot will not glow red..

I don't know the actual temperature at which iron or steel starts to glow red, but I think it's in the mid 800* range, bright red is around 1100* I think,, I'm sure you can google it.
So there are plenty of people who on really cold nights will run their stoves with a surface temperature of 600*, and that is making a LOT of heat.. how much would depend on each make and design of stove.

The BTU figures are based on the quantity of coal being burnt, and the ability to get air to it to sustain a high burning rate..
You won't find a handfired stove with a shoebox sized firebox claiming 100K BTU, probably about 40K BTU, but a big harman Mark III or SF250?? those fireboxes are BIG and hold a lot of coal, aka Hard BTU's.. so if you can supply enough air to get it all burning hot, yep, it will probably make the advertised BTU's..

For example: an AA 260 turns it's auger twice as fast as an AA 130, twice the coal is available to burn at max output. All part of
the design.. I'll bet that an AHS 260 would have a bigger feed hole in the bottom of the hopper than an AHS 130.. again, part of supply for output.

I don't think the BTU claims are lies, that's for sure, but some may be overly optimistic but still not off by huge percentages.

Just my take on it.
Greg L

LsFarm wrote:The BTU figures are based on the quantity of coal being burnt, and the ability to get air to it to sustain a high burning rate..
You won't find a handfired stove with a shoebox sized firebox claiming 100K BTU, probably about 40K BTU, but a big harman Mark III or SF250?? those fireboxes are BIG and hold a lot of coal, aka Hard BTU's.. so if you can supply enough air to get it all burning hot, yep, it will probably make the advertised BTU's..

You also need commensurate heat exchange surface which these stoves don't have, and the higher the firing rate the less efficient it will be as stack temperature accelerates requiring even higher firing rates.

As for boilers, if it does not have an IBR rating I would not trust it.

franco b wrote:
As for boilers, if it does not have an IBR rating I would not trust it.

Why?

I think a BTU rating should just be used as an approximation as we mostly use them to roughly size a heater. So an a sophisticated heat loss measurement on your property estimates you need a 123,000 BTU heater that is not what you buy as it does not exist. In this example you look at the 150,000 to 200,000 BTU units and pick on other factors. As long as all stove suppliers play the same game the same way the semantics of measurement are irrelevant. After all the heat loss study is an approximation as well and mother nature does not abide by your estimation of minimum temperatures/windchill. I think that any stove operating flat out, with the possible exception of electrical units, does not run efficiently at it's maximum. So it ascribes value to the coalnewbie theory "overkill is great and more overkill is better". It does not always apply as there can be inefficiencies if applied stupidly, but it is surprising to me how often it is a good rule to live by. Forget BTU other than as a rough guide, it's heat transfer that is the god that needs to be worshipped. It's where the hydronics crowd has the home field advantage but there are other considerations in my view. Your praying at the wrong altar.

coalnewbie wrote: So it ascribes value to the coalnewbie theory "overkill is great and more overkill is better".

x2. I think that theory was widely held and practiced by the Dead Men, and that there are many logical reasons for it in the context of coal heat.

Mike