Old topic revisited: How does a stove get its BTU rating?

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: franco b On: Thu Sep 19, 2013 5:50 pm

lsayre wrote:This probably means they are using the grate area, which would be a bit less than the firebox area. I wonder how well this simple grate area formula works for other hand fired stoves?

It doesn't work for DS Machine or any other stove as well when the figures are so inflated beyond what is reasonable.
franco b
 
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: lsayre On: Thu Sep 19, 2013 5:56 pm

franco b wrote:
lsayre wrote:This probably means they are using the grate area, which would be a bit less than the firebox area. I wonder how well this simple grate area formula works for other hand fired stoves?

It doesn't work for DS Machine or any other stove as well when the figures are so inflated beyond what is reasonable.


Agreed! Then perhaps the question should be, how well does 200 times the grate area equate to a hand fired stoves BTU's?
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: franco b On: Thu Sep 19, 2013 6:49 pm

lsayre wrote:Agreed! Then perhaps the question should be, how well does 200 times the grate area equate to a hand fired stoves BTU's?
It works a lot better but it still is a starting point for a stoves design. The extent of heat exchange area as well as how efficiently that heat exchange works effects the size and efficiency of the stove. Tending intervals at a given Btu output will also govern the size of the fire pot as well as the grate area. If you want a stove to burn 100,000 Btu of coal and tend it every 12 hours then that's about 10 pounds per hour or 120 pounds in 12 hours. There still has to be burning coal left to ignite the new charge so the fire pot would have to hold about 180 pounds if you wanted to keep 12 hour tending times. That's why those old central heating furnaces and boilers were so big. The ratings on new stoves are what can be achieved burning flat out for a few hours.

The best measure of a stoves heat output is still size. The square feet of heat exchange surface which will emit a given amount of Btu at a certain temperature provided that temperature is reasonable. From 400 to 600 it more than doubles but to maintain 600 degrees as an average on the entire stove is not practical.


Temperature of Surface Fairenhiet -------------- Total Energy Transferred BTU's per hour per foot

80* ------------------------------------------------------ 15 Btu's / Sq.Ft.
100* ------------------------------------------------------ 51 Btu's / Sq.Ft.
150* ------------------------------------------------------ 168 Btu's / Sq.Ft.
200* ------------------------------------------------------ 315 Btu's / Sq.Ft.
400* ------------------------------------------------------ 1230 Btu's / Sq.Ft.
600* ------------------------------------------------------ 2850 Btu's / Sq.Ft.
800* ------------------------------------------------------ 5430 Btu's / Sq.Ft.
1200* ----------------------------------------------------- 9370 Btu's / Sq.Ft.
franco b
 
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

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Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: lsayre On: Thu Sep 19, 2013 7:10 pm

It seems to me that some independent organization akin to UL should heat coal stoves to perhaps 700 surface degrees F. over some logically selected area and then measure the heat rise in a standardized and outwardly climate controlled room, from which they can validly compute the output BTU's required to accomplish such a measured level of heat rise over a period of time such as one hour. Then see how much coal was consumed in doing so (perhaps have the stove on a scale the entire time, shake down when 700 degrees is first reached, then shake down again after one hour at 700 degrees, then remove the ashes and re-weigh what remains) and thereby compute the input BTU's which match the output BTU's. This leads to the stoves efficiency rating when at high fire. In the end you have, input BTU's, output BTU's, and efficiency that can all be believed.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: lsayre On: Thu Sep 19, 2013 7:29 pm

Hitzer's 50-93 has a firebox that measures 25" x 13.5". Using 375 BTU's per square inch of firebox (in an attempt to compare it directly to DS Machine) it ranks as follows:

25 x 13.5 x 375 = 126,563 BTU's
Last edited by lsayre on Thu Sep 19, 2013 9:09 pm, edited 1 time in total.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: JRLearned On: Thu Sep 19, 2013 7:56 pm

The best post I've seen on this question, and the most accurate calculation, IMO, is here: http://nepacrossroads.com/about15468.html

GRATE AREA SQ.FT. x .65, THE PERCENTAGE OF EFFICIENCY x 8, THE POUNDS OF ANTHRACITE PER SQ.FT. x 12,500, THE AVERAGE BTU'S PER POUND OF ANTHRACITE.

I think the calculation here is pretty accurate and that its all about grate size. The DS machine stoves all post a btu rating and the grate size is the only real difference in their stove models that impacts the ouput.
JRLearned
 
Stove/Furnace Make: Chubby Stove
Stove/Furnace Model: FrankenChubby

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: franco b On: Thu Sep 19, 2013 8:09 pm

JRLearned wrote:The best post I've seen on this question, and the most accurate calculation, IMO, is here: http://nepacrossroads.com/about15468.html

GRATE AREA SQ.FT. x .65, THE PERCENTAGE OF EFFICIENCY x 8, THE POUNDS OF ANTHRACITE PER SQ.FT. x 12,500, THE AVERAGE BTU'S PER POUND OF ANTHRACITE.

I think the calculation here is pretty accurate and that its all about grate size. The DS machine stoves all post a btu rating and the grate size is the only real difference in their stove models that impacts the ouput.

What it doesn't solve for is how to burn 8 pounds per hour on a one square foot grate.
franco b
 
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: lsayre On: Fri Sep 20, 2013 6:26 am

franco b wrote:What it doesn't solve for is how to burn 8 pounds per hour on a one square foot grate.


Can it be done at all (sans for accidentally leaving the ash door and the manual damper wide open), and if it can be done, would the surface temperature be greater than 700 degrees? Why rate stoves at BTU levels that may not be safe to achieve at a reasonable maximum surface temperature? What is needed are BTU ratings for the "nominal" maximum safe and sustainable BTU output of the stove. This is how it appears the European stoves are rated.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: lsayre On: Fri Sep 20, 2013 6:43 am

I find it interesting that the same source that claims 8 lbs. can be burned per hour for every square foot of grate regarding nut coal indicates that only 5 lbs. can similarly be burned for pea. The relevance of this to me (since I'm contemplating burning pea in a hand fired) is that pea will only give me about 63% of the heat output that I could achieve with nut. This is the first time I have ever seen an attempted quantification of the difference between pea and nut in a hand fired stove.

Putting a range of concepts from this thread together, if I purchased a HFH-90, and it is rated at 90,000 BTU's.
1) Assuming the European ratings to be better (likely from a safety perspective), that would mean it is capable of safely delivering only 45,000 BTU's per hour.
2) Assuming the above to be for nut, with pea it would be capable of safely delivering 5/8th's of that, or 28,000 BTU's per hour.
3) Using 12,500 BTU's per pound, at 28,000 BTU's per hour it would consume 54 lbs. of pea per day.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: freetown fred On: Fri Sep 20, 2013 7:11 am

And here I thought I had WAY to much down time on my hands! :clap: toothy My question would be---can anyone sum up ( or paraphrase, for you brainiacs) these last two pages into a short paragraph so a regular workin grunt like myself might understand whatever the outcome might be here?
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: Rigar On: Fri Sep 20, 2013 7:14 am

freetown fred wrote:And here I thought I had WAY to much down time on my hands! :clap: toothy My question would be---can anyone sum up ( or paraphrase, for you brainiacs) these last two pages into a short paragraph so a regular workin grunt like myself might understand whatever the outcome might be here?


...the bigger and hotter the fire...the more BTU s ??? :lol:
Rigar
 
Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: freetown fred On: Fri Sep 20, 2013 7:29 am

Thank you Rigar--THAT I understand ;)
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: Rigar On: Fri Sep 20, 2013 7:35 am

my pleasure FF.... :D
Rigar
 
Hot Air Coal Stoker Furnace: Keystoker A 150
Coal Size/Type: anthracite rice
Stove/Furnace Make: Keystoker
Stove/Furnace Model: A 150 warm air furnace

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: Stanb999 On: Fri Sep 20, 2013 7:47 am

franco b wrote:
JRLearned wrote:The best post I've seen on this question, and the most accurate calculation, IMO, is here: http://nepacrossroads.com/about15468.html

GRATE AREA SQ.FT. x .65, THE PERCENTAGE OF EFFICIENCY x 8, THE POUNDS OF ANTHRACITE PER SQ.FT. x 12,500, THE AVERAGE BTU'S PER POUND OF ANTHRACITE.

I think the calculation here is pretty accurate and that its all about grate size. The DS machine stoves all post a btu rating and the grate size is the only real difference in their stove models that impacts the ouput.

What it doesn't solve for is how to burn 8 pounds per hour on a one square foot grate.



The reason your having issues with the math is hand fired stoves are more efficient than 63% in actual use. Properly setup they can be and and are generally in the 80% range. Especially at lower burn rates which we all use, (few of us have the stove glowing red on an average burn). Well tuned for the room temp(no up and down on the air intake, steady burn rates). So by slowing the air you increase the efficiency of the stove drastically and easily.

For example...

12500 btu x .65 = 8125
@ 70% 8750
@ 75% 9375
@ 80% 10000


One other thing to realize is they are trying to compare the stoves to a furnace... A 2000 SQ house needs x size furnace to heat it well. What is ignored is that furnace runs 25-30% of the time even on the coldest days. So you'd have to half their rating or double the output of the stoves for the obtuse to understand that it doesn't take 100,000 BTU's an hour to heat a 2000 SF home... Even tho his furnace is that big.
Stanb999
 
Stove/Furnace Make: Harmon
Stove/Furnace Model: Mark II

Re: Old topic revisited: How does a stove get its BTU rating?

PostBy: freetown fred On: Fri Sep 20, 2013 7:50 am

Hey Stan, where the hell you been??????????????? AND you jump in for THIS ONE--- :clap: toothy Nice to see you're alive & well my friend:)
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

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