Someone on CT was enquiring what the Whale blown air heating system would take out of the battery on an Orion without EHU.
There was a very useful reply from Dave which I repost here with permission :
The Whale space heater takes 0.01amps when it's on, and 1.6 amps with the fan running. If you assume a 50% duty cycle (i.e. fan running about half the time - depends on how cold it is), you are looking at about 0.8amps average = about 20ah a day.
So assuming a 110ah battery and not running the battery down less than half way and considering that there is other usage ( 12v TV,water pump,toilet,lights ) then that is about two to three days on continuously,depending upon how cold it is of course.