How to size the unit heater?

[yesky]

The garage door is 20'x7', winter temp. is -20F, in garage Temperature is 50F. How to calculate the heat loss and unit heater size? I think I need wind velocity x 20'x7' to get the cubic feet per min (CFM) then multiply 1.08 and temperature increases to get the total heat loss. If I use this to calculate, then I need a very large kW unit heater.

Please give me an advice on how to calculate the heat loss when door is open.

 

[rburke65]

First of all, Welcome to Garage Journal....a lot of nice folks here. Next, I would think heat loss, at -20°, from a 20'x7' door....140sq.ft....would be...????...100%! Just a guess. What state do you reside...or is it a secret?