If you are looking at about 7500 watts that is a 40 amp breaker with the 125% factor applied. You'll need two slots to install that breaker. I have no idea what panel you have but I'd bet that tandem breakers are available for it. By doubling up two existing branch circuits you'd have the space available. For what you are doing, I think this would be the way to go versus the non-vented propane heater.

Tandem Breaker Example

twocents

"We live in a time when intelligent people are being silenced so that stupid people won't be offended".