Bottom Line Up Front (BLUF): It takes about 7 minutes per gallon per 1000W available power to heat milk from fridge to cheese making temp. My set up, with about 1500 watts and about 15 gallons would take 68 minutes, under ideal conditions. Add in 30% loss in efficiency (I have no idea is that's a good number) it will take about 97 minutes-too long. I'd need 2 circuits or a higher amp circuit.

This an energy problem. If I use this kind of heating element, the question is, can I get enough energy from the wires in my wall into the milk, at a good rate (not too fast, as that scalds the milk, not too slow because that invites contamination). So, let's start with a quick look at how much energy I need. We'll assume we have 100% effecifiency--that is, all of the energy goes into the milk, none to the sink, none to the air. If we say I'm going to do a 15 gallon batch, that is 56.8 L (we'll use metric because it's easier). If we assume that milk has a heat capacity similar to that of water and that the heat capacity doesn't change much within the range of temps used in cheese making, then to raise the temperature 1 C, we need 4.18 Joules of energy for every gram of milk, and using the density of water, we have 56,800 grams of water. That means, we need 237,424 Joules to raise the entire vat 1 C. If the milk comes from the fridge at 4 C and we want to bring it up to 30 C, we need 26 C * 238,000 Joules/C = 6.17 Million Joules. If the max power I can draw from a single 110V circuit in my home is 1500 W ( a Watt is a Joule/sec), then it will take me 68 minutes to heat the milk. A more portable number, perhaps is that it takes just under 7 minutes to heat 1 gallon of milk (from 4 to 30 C) with 1000 Watts directly to the milk. If we guess that we have about 30% loss (which I think it pretty high compared to what I'd really have, but again, I have no practical experience with this) then that bumps everything up, so 98 minutes for my scenario. I need a higher amp circuit or to use two circuits.