How many BTUs does my burner need?

Equipment — By on April 9, 2008 at 8:52 pm

The other day I made beer with my new 25 gallon pot and I confirmed what I suspected:  A 55,000 BTU burner cannot boil 15 gallons of wort in any reasonable amount of time.  My brewing day was cold and windy, so I never got the wort above 200°F (93°C).  The question I needed to answer is how many BTUs do I need to boil my wort?

What is a BTU?

A BTU (British Thermal Unit) describes the amount of energy to raise 1 lb of water 1 degree Fahrenheit in one hour.

lbs of water x temperature rise = BTUs required for one hour
(1 lb of water x 1 degree Fahrenheit) = 1 BTU for 1 hour

Water equals 8.3 lbs per gallon.  To boil one gallon of water starting 70°F in 1 hour you will need 8.3 x (212-70) = 1,178.6 BTUs.  On my brewing day, I needed 15 x 1,178.6 = 17,679 BTUs to boil my wort in an hour.  With my 55,000 BTU burner, I should have no problem boiling my wort right?  The total boil time should take about 20 minutes.

burner

This burner does 210,000 BTUs and can burn a hole in the sun, but is it too much?

What’s wrong with the calculation?

This calculation assumes the heat transferred from your burner to your water is 100% efficient.  This will never happen no matter how much you beg the beer gods.  The BTUs listed on your burner are like mileage listed in a car.  Your mileage will vary.  On a nice hot day (unlike my brewing day), 50% is a good number to hope for.  Under ideal weather conditions, my boil time should be around 40 minutes with a 55,000 BTU burner.  Less than ideal brewing days can drastically increase your boil time.

Another factor to consider is evaporation.  Evaporation removes energy from your wort.  This means you need additional energy just to keep your wort at a boil due to heat loss and evaporation.  Boiling your wort down one gallon will require another 8,000 BTUs.

boiling wort

You should also consider how efficient your burner is, not just how powerful


Since I started 17 gallons (boiling down to 15 gallons) of wort, I needed 17 x 1,178.6 = 20,036 BTUs.  I was boiling down 2 gallons, so this adds another 16,000 BTUs for a total of 36,036 BTUs for one hour.  Assuming 50% efficiency, I needed 72,072 BTUs to boil the wort in one hour.  On my cold brewing day, I would have been lucky to get 25% efficiency.  I needed a bigger burner, and if I had calculated it this in advance I would have known (instead of suspected) it.

My 55,000 BTU burner would have been ok for a 5 gallon brew, but scaling to a much larger brew I needed a bigger burner.  The next day I purchased a 210,000 BTU burner (I tell people it has enough power to burn a hole in the sun).  Taking the above equations into account, hopefully this will help you make an educated decision on which burner to use.

I am a avid homebrewer and winemaker. I’ve been making my own beer and wine for many years. I started making beer when I was in college (mostly because the drinking age in the United States is 21). My first few beers were horrible. The beers are much better now, and I often supply my neighborhood with free beer!

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  • Brandon Lesniak

    where is a good place to shop for these burners? I currently do partial mashes on my stove in my apartment. I'd like to eventually get or make my own equipment so I could do full mashes. Right now just 5 gallons at a time but eventually I'll want I think 15 gallons at a time. I dont want to replace pots and burners so rather have equipment I can grow with from 5 gallons up to my desired 15 gallons. Any suggestions would be great. Thanks!!

  • http://www.fermentarium.com deege

    I usually get my stuff from either NortherBrewer.com or MoreBeer.com. Both places will have the burner I got, and pots of every size. I do 15 and 20 gallon brews in a 25 gallon pot. I batch sparge, so I'm using 1 or 2 coolers for the mash. That means I only need 1 big pot. I also have a smaller 10 gallon pot, which is good for boiling sparge water or even making a second smaller beer at the same time (if you have more burners).

  • Kevin humphrey

    Can you use a Turkey fryer?

  • http://www.fermentarium.com deege

    Yes, many people do. You might have to adjust the recipe size if your pot holds less than 5 gallons.

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  • J Neric

    How did you come up with  “8,000 BTU” requirement to boil down 1gal?. thanks!

  • Lacudda

    For future readers, it’s about 970 BTUs / pound of water for steam generation so 2 gallons = 16.6lb or 16100 BTUs. I’m guessing this is what he used and it’s not exact. More of a guess. You need to calculate the amount of heat needed to heat water then add the amount of heat to undergo a phase transition (from liquid water to vapor water, or stem). That’s the correct way to determine energy needed and wort requires more energy than pure water does so keep that in mind.

  • Lacudda

    It would be nice if I could only spell. Stem = Steam!!

  • verplanck

    also, remember that you aren’t boiling pure water, you’re boiling wort, so it will take more energy to bring it up to temp.