Electrical Circuits in my Greenhouse
You are, looking for trouble &amp; you'll get it. You must run each heater on a separate circuit, they will not run on the same circuit. A proper 20amp circuit will only handle 2000-watts or 17amps safely &amp; continuously.

Look at the bottom or back of the heaters for how many Amps they use or require. You'll need an Electrician to re-wire the heater area if they are where you would like or need them to be.