Subject: BTU Ratings
Date: 1989-11-14 14:38:00 GMT
Guy Ruth asks about BTU's and batch size:
> With a little calculation, I was able to figure that a minimum heat source
> should put out approx. 15,000 BTUs. I used the following figures:
> 31 gallons @ approx. 8#/gallon
> 1 BTU to raise 1# of water 1 degree F
> temperature change of 60 degrees to achieve boiling
> 14,880 BTUs
I think 15,000 BTU's are way too little for boiling 31 gallons of wort.
Missing from these calculations are any thermal losses. If the kettle is
perfectly insulated, and no heat escapes from the lid, 15,000 might be enough.
I believe stoves are rated in BTU/hour. WITH NO THERMAL LOSSES you will get
your water to 200+ degrees in an hour. It has been a long time since
thermodynamics class, but also missing is the energy necessary to bring 212
degree water to 212 degree steam. (I recall the 'delta-H' of transformation
being 10 kcal/mol - I can't convert this to BTU's, but I believe this is
significant.) A 15,000 BTU burner will NEVER get 31 gallons to boil.
I have friends who use Coleman-type propane burners (available from a sporting
goods store) rated at 26,000 BTU. They are great for boiling six or seven
gallons of wort. They heat the wort in a hurry (<20 minutes) at full
throttle, and keep a moderate boil going when throttled back.
Personally, I use a 120,000 BTU propane burner. It sounds like a jet engine.
It was marketed at a "Creole Cooker"; I cook Creoles in it :-) 120,000 BTU is
way overkill for 6 gallons of wort! Even throttled back, I have difficulty
controlling the boil. I suspect that it would be sized 'just right' for 31
gallons of wort.
I have another colleague who brews in 25 gallon batch sizes. He uses an
industrial kitchen stove. He got it from a restaurant. I don't know its BTU
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