Yes, you can easily use a patio heater on a covered porch. If you are using an electric patio heater, you will need to place it near an electrical outlet. If it’s a gas heater, you can place it pretty much anywhere.
You have to be careful about one thing: ceiling clearance. Standing patio heaters can be as tall as seven feet. You do not want the flames too close to the ceiling. The heat can damage the ceiling, and also it’s a fire hazard.