There have been a few requests for more info about the tank heaters Airstream installed, so here's what I know. Sorry to say it's not much. They're made by UltraHeat (Ultra Heat, Inc. - Home
), which manufacturers several different types, including tank heaters, pipe heaters, and elbow heaters. Airstream doesn't indicate which type is installed, but my hunch is that they're tank heaters. I can't be sure, because the tanks are enclosed in metal pans, and it would be a real hassle to remove one.
In any case, the Model TH-618 Tank Heater (probably the one on my trailer?), draws 6.1 Amps at a nominal 13.5 VDC. It's thermostatically controlled so that if it's enabled (by flipping switches in the trailer's bathroom to "on"), the heater comes on when the tank temperature drops to 44 degrees fahrenheit, and it turns off at 64 degrees.
The good news is that the heater isn't always on when the trailer's switch is in the "on" position. It only comes on when the tank gets cold. But the bad news is that it draws a lot of current while it's on. In a tank that's nearly full, I think it might take quite a while to warm the fluids from 44- to 64-degrees. On the plus side, though, once 64-degrees is reached (and the heater turns off), it would take quite a while for the temp to drop back down to 44. Still, if the heater is running for 5 hours during a cold night, it will consume more than 30 amp-hours of electricity. Something I'd definitely like to avoid unless I'm plugged-in to shore power.
Hope this info is helpful! And thanks again for the great tips for keeping my tanks from freezing.