You can use any heating source inside, like electricity, gas, propane, and even wood. It may be tricky to heat with wood, as you want to ensure that you keep the stove/pit away from the panels to prevent them from melting or burning if they are too close to the fire source. In this case, the customers ideally would want to come up with an exhaust system, making sure it’s not in contact with the panels, for being a flammable material.
