1) No need to keep going back and forth trying to figure out what size heater you need. Again;

http://www.ultimategarageheater.com/garage-heater-calculator.php

you will note that your 400sq ft. garage (insulated) needs about 4.4kw (approximately 15,000 BTUH) for a 60 deg F temperature change.

2) All commercial electric heaters are rated in KW, but no matter as long as you realize that 3414 BTUH = 1kw it's simple math to go back and forth.

3) ratings per square foot are pretty rudimentary (even more so than the simple calculator I linked above) and doesn't take into account ceiling height, insulation, # and type of doors and windows, exposure, etc, etc.


Just my as I do this for a living.

Dave


This is good info ...
Thanks,
Chris.