 How many BTU's per hour? sonhouse Posers and Puzzles 22 Sep '08 03:29
1. 22 Sep '08 03:29
So I have this electric water pot, I put in exactly 5 cups of water at the start is 50 degrees F and it goes to 212 in exactly 5.5 minutes. How many BTU's/hr does that represent? Assuming it could go on for an hour of course.
2. 22 Sep '08 10:561 edit
Originally posted by sonhouse
So I have this electric water pot, I put in exactly 5 cups of water at the start is 50 degrees F and it goes to 212 in exactly 5.5 minutes. How many BTU's/hr does that represent? Assuming it could go on for an hour of course.
Assuming 1 cup = 200 cc:

change of (212-50) degrees F = change of 90 degrees C

200 * 90 = 18000 little calories

1 BTU = 252 calories

so the energy produced was 18000/252 ~ 71.4 BTU

71 BTU / 5.5 min = 71.4 BTU / 0.092 hours ~ 780 BTU / hour

If 1 cup is 250 cc the answer is ~ 975 BTU/hr. (according to wikipedia "There is no internationally agreed standard definition of the cup, which ranges in volume between 200 and 250 millilitres." )
3. 22 Sep '08 13:041 edit
Originally posted by David113
Assuming 1 cup = 200 cc:

change of (212-50) degrees F = change of 90 degrees C

200 * 90 = 18000 little calories

1 BTU = 252 calories

so the energy produced was 18000/252 ~ 71.4 BTU

71 BTU / 5.5 min = 71.4 BTU / 0.092 hours ~ 780 BTU / hour

If 1 cup is 250 cc the answer is ~ 975 BTU/hr. (according to w ed standard definition of the cup, which ranges in volume between 200 and 250 millilitres." )
The old definition of a pound is useful here: A pint's a pound the world around. So one pint is two cups and I have 5 cups boiling therefore 2.5 pints or 2.5 pounds. BTU's are defined as the amount of heat energy it takes to heat one pound of water one degree F. So it takes 2.5 BTU/degree
and the temperature change is 212-50 which is a 162 degree F change. So 2.5 times 162 is 405 BTU's expended to heat that amount of water. The thing you neglected is it did that job in 5.5 minutes so if it did that for one hour it would be 10.909 times 405 for a grand total of 4418.18 BTU's per hour if it went on at that sustained rate which is what I was after.
10.9 comes from dividing 60 minutes in an hour by 5.5 minutes=10.909.
So it comes out to 4418.18 BTU's per hour which is the energy expended to heat 27.27 pints (pounds) of water 162 degrees in one hour.
4. 22 Sep '08 16:36
Originally posted by David113
Assuming 1 cup = 200 cc:

change of (212-50) degrees F = change of 90 degrees C

200 * 90 = 18000 little calories

1 BTU = 252 calories

so the energy produced was 18000/252 ~ 71.4 BTU

71 BTU / 5.5 min = 71.4 BTU / 0.092 hours ~ 780 BTU / hour

If 1 cup is 250 cc the answer is ~ 975 BTU/hr. (according to w ...[text shortened]... ed standard definition of the cup, which ranges in volume between 200 and 250 millilitres." )
CORRECTION: I forgot you warmed up 5 cups of water, not 1 cup. So multiply my final result by 5.
5. 22 Sep '08 23:541 edit
Originally posted by David113
CORRECTION: I forgot you warmed up 5 cups of water, not 1 cup. So multiply my final result by 5.
That makes it a bit closer but you don't need the calorie to btu conversion when you know a pint's a pound and one btu is the energy needed to heat up one pound of water one degree F.
6. 23 Sep '08 09:33
Originally posted by sonhouse
That makes it a bit closer but you don't need the calorie to btu conversion when you know a pint's a pound and one btu is the energy needed to heat up one pound of water one degree F.
A pint seems to be a pound only in America. A pint is 568ml (20 floz) here.

This might also explain why Americans get drunk so easily.
7. 23 Sep '08 10:591 edit
Originally posted by Schumi
A pint seems to be a pound only in America. A pint is 568ml (20 floz) here.

This might also explain why Americans get drunk so easily.
That is mainly for beer flagons isn't it? The BTU means the British Thermal Unit so it didn't start in the US. If your pint is 20 fluid ounces, that is 4 ounces more than the US version at 16.
8. 23 Sep '08 14:00
Originally posted by Schumi
A pint seems to be a pound only in America. A pint is 568ml (20 floz) here.

This might also explain why Americans get drunk so easily.
Yep, pints are 20 fl. oz. in Canada, too. But that's not the only problem...what do making love in a canoe and American beer have in common? They're both f***ing close to water.
9. 24 Sep '08 02:14
Originally posted by PBE6
Yep, pints are 20 fl. oz. in Canada, too. But that's not the only problem...what do making love in a canoe and American beer have in common? They're both f***ing close to water.
very true indeed!😉
10. 24 Sep '08 03:29
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11. 12 Oct '08 14:52
Originally posted by sonhouse
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