I suspected that might be the case. We do have a new 20A outlet so we might be getting a bit more of a charge than someone with an older 15A outlet in their garage.
The pipes run from the boiler into the garage before entering the rest of the house. Honestly, we just lucked out, because we hadn't read anything about EVs so we didn't know that heat would matter. Glad that we have it though! Next up: insulating the garage door.
Um. What follows is Charging 101.
15A socket has breaker, wire, and mechanical socket all rated for 15A. NEC says with constant, heavy load (hello, Tesla!) one must derate by 20%. This is to prevent, and I am not kidding here, Fires. So, with 15A, 80% of 15 = 12A, and the power available to Charge Ye Car is 120VAC * 12A = 1440W.
Note that the power to heat the battery to the point of being able to charge it is a 2 to several kW if it's below freezing. So, that's why 1.44 kW won't cut it with outdoor cars in the NYC area.
A 20A circuit has a breaker, wire, and socket that are truly, duly, rated for 20A. A NEMA5-20 has that kind-of-unique right-angle blade to show it. Power available is still subject to that 20% rule, so 20A * 80% = 16A, giving 120VAC * 16 = 1.92kW. Instead of 4.5 to 5 miles of charge per hour, one gets six or seven. Still not enough to heat the battery, though.
Going to 240VAC changes things quite a bit. A LR or P version of a Tesla can accept 48A; the SR maxes out at 32A. So, with a Wall Connector, hard wired to a 240 VAC circuit, one can get 240VAC * 48A = 11.52 kW. Which can heat up the battery in a car, outdoors or not, no problem. One also gets 45 or 46 miles of charge per hour.
Tricky bit: A given breaker box can handle "yea" amount of current. I've personally seen breaker boxes on houses built 40 years ago that had, for the entire breaker box, a 60A main breaker. And all the extra slots used up. Clearly, one isn't going to get 48A for a Tesla out of one of them. My place got built with a 200A main, as it happens, so sticking a 60A duplex breaker for 240 VAC wasn't an issue.
Electricians run something called a "Load Analysis" to figure out how much spare current is available. There's lighting, more or less based on the square footage of the house, and the rated power of Every Single Appliance in the place. All these numbers get put into a chart and, more or less counting fingers, they figure if your house can support whatever extra you've got in mind.
Thing is, if one can't stick a 60A breaker in there, one might be able to stick a 20A, 30A, or 40A breaker, then jigger the Tesla Wall Connector to match. A 40A breaker gives one 32A after the derating, and 240VAC*32A = 7.68kW. Which is still enough to fully charge a Tesla overnight, as well as getting it heated, if that's necessary.
Fun.