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Brew Kettle BTU CalculationsBTU Losses during BrewingA lot of customers have asked over the years how many watts of power they need for their electric brewery. I've been able to give estimates based on the actual BTUs needed to heat water + 30% for loss, but my answer has never been exact. So, when I finally sat down and calculated real world losses I decided to use a converted beer keg or keggle because they make a great brew pot & a lot of 10 gallon brewers use them. Keggles hold 14.5 gallons of beer which makes them the perfect size for a 10 gallon batch. To calculate BTUs needed and heat loss we need to start with the basic stats: 30#  Weight of a empty beer keg Then I found these standards in a published Engineering table: This table lists BTU/hr loss per square foot in a steel tank with no insulation, assuming the temperatire outside the tank is 70F.
So, using basic stats & the
Engineering Table I found, I can calculate heat loss in BTU
/ hr, assuming you are boiling 12 gallons of water.
BTUs to Heat MASH WaterA typical 10 gallon grain bill for me is 20 pounds & I will heat 7 gallons of mash water to 170F and mix with my mash which will drop the temperature to less than 130F. I'll use my RIMS tube to bring my mash the rest of the way to 145F. Using the weight of the keggle (30
pounds) + 7 gallons of water, I calculate about 61.98 BTU /
hr to raise the temperature one degree F.
But let's look at the same graph with
heat loss added in.
BTUs to Heat Sparge WaterA typical 10 gallon grain bill for me is 20 pounds & I will heat 9 gallons of sparge water to 170F to rinse the sugars from my grain bed. Using the weight of the keggle (30
pounds) + 9 gallons of water, I calculate about 78.66 BTU /
hr to raise the temperature one degree F.
But let's look at the same graph with
heat loss added in.
BTUs to Reach BoilFor a typical 10 gallon I usually cut off my sparge at 12 gallons. This gives me enough volume for a 60  90 minute boil. Using the weight of the keggle (30
pounds) + 12 gallons of water, I calculate about 103.68 BTU
/ hr to raise the temperature one degree F and my starting
temperature is usually about 150F
But let's look at the same graph with
heat loss added in.
My Take on ThisI mentioned earlier that most of the heat loss is through evaporation. Go back to my BTU Loss graph and you'll see that evaporation loss becomes the largest heat loss past 180 degrees F. Keeping the lid on your hot liquor tank and keeping the lid on your brew kettle until almost boil eliminates almost all of your evaporation heat loss. The next step would be to insulate your hot liquor tank and brew kettle to reduce heat loss. And finally, it's impossible to brew 10 gallon batches with a 1650 or 2000 Watt element and time consuming to brew with a 3500 Watt element. But a 4500 Watt or 5500 Watt element will work great.


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