I have a 4X8 Ft. panel and a fan that hooks to a thermostat but doesn't heat enough. My shop is 24X40 ft. I live tn east Tn. so it doesn't get real cold here. I'm building a 19X19 ft. addition to my shop that faces east and want to heat it with the air space between my roof and insulated ceiling (forced air) what would be the best way to do it?