Here's mine, $110 20×20 hx of the bay, free fan from local HVAC co., $20 of tin box they knocked together for me, and a 110v t-stat. The fan pressurizes the box for more even flow through hx. This is how they told me to do it, after explaining what i was doing. To keep a 24×30 insulated building at 50° on a 15-20° day it only runs 2 minutes every 50 minutes. I leave heat on all the time, the little bit of heat it draws why shut it off? It would take a lot of heat to warm all the steel in the building. Its a lot easier to get to 70° from 50° this way. Not to mention tools are always warm when you grab them!
