Bringing water or wurt from tap or room temperature takes a tremendous amount of energy, measured in BTUs. And one BTU is the amount of energy needed to raise one pound of water one degree F (Fahrenheit). The easiest way to understand what BTUs are is to to calculate the number of BTUs needed to bring 12 gallons from 150 degrees F to boil – and the calculation is:
1 (BTU) X 12 (gallons) X 8.3 (weight of one gallon) X 62 (degrees difference) = 6175 BTUs.
In other words, in a perfect world it will take 6175 BTUs to bring your 12 gallons of wurt from 150 degrees F to boil.
And once you reach 212F you need to factor the energy needed to boil – to convert part of your wurt into steam, which is an additional 8000 BTU per gallon. So, starting with 12 gallons and ending with 10 gallons you need a total of 6175 + 8000 (for gallon 1) + 8000 (for gallon 2) or 22,175 BTUs. .
BTUs from Propane Gas
Don't believe the advertising on TV when they claim gas is better than electricity - they are only right when it comes to natural gas, not propane gas.
Also, things get complicated when it comes to gas brewing - you have to consider heat transfer loss, which for any gas fired system usually starts at 50% and can reach higher depending on surrounding (weather) conditions. Start dealing with a cross wind or very cold brewing conditions and a gas fired backyard brewing setup can easily have a heat loss of 75% or more. This puts energy needed from gas at a staggering 44,350 BTUs to 88,700 BTUs. And don’t forget, you used the same propane gas to raise your mash water & sparge water up to temperature. Add 25% more for mash & sparge, and at current propane prices your total gas cost will run at about $4.50 - $9.00 per 10 gallon batch of beer.
BTUs from 120V or 240V Electric
Everything changes with electricity. When you use a submerged electric element your heat source is 100% surrounded by your wurt and the only heat that escapes is the heat that is radiating through the sides of your pot & escaping through the top. This means that almost 100% of the energy you put into your electric element gets transferred to your wurt. And at an overall efficiency is 90% or better, you will need 24,639 BTUs from electricity.
One watt of electricity = 3.41 BTU/hr, so 24,639 BTUs will require approximately 7225 total watt/hrs. Actual cost to you depends on your local utility rate but at North Alabama’s current rate of $0.08416 per KWh and adding 25% more electricity for mash & sparge, and the electricity cost of brewing a 10 gallon batch will be about $0.75.
This site is owned and operated by Tom Hargrave Sales