That would be useless in that big of a space
Depends if OP has insulated garage or not. Sounds to me like OP is looking for
temporary heat with propane. Since he doesn't say I'm assuming he DOES have insulation. Also, assuming he's NOT in Antarctica, as he's thinking of using "patio heater"
inside a garage.
The Big Buddy will crank out 18K Btu and with the AC/DC electric cord, it has it's own built-in fan. He'd need optional hose kit and 20 lb BBQ bottle of propane, then OP would have 23'x31' garage warmed up in 30 minutes. Once the OP got his permanent heat going, then the Big Buddy would be backup or spot heater.
Conversely, the OP's idea of patio heater will result in undesirable / UNSAFE heat in garage, plus a patio paperweight when he gets permanent garage heat.
