Can I run my heaters on only 120 volts of power?

Using an 110/120-volt heater (1,500 watts maximum) is fine for enclosed areas like garages, indoor work areas, or outdoor spaces no larger than 5' x 5'. When heating larger areas, running a dedicated 110/120-volt circuit is not practical or economical. A 240-volt circuit will require the same amount of wiring, will heat substantially larger areas with greater comfort, and will simply require two spaces in the breaker panel, rather than one.