It's fine (but not great) to install a thermostat above the heater
Placing a wall thermostat directly above a wall heater is not ideal.Putting a thermostat directly above a heater is OK, but not ideal. That's because when the heater turns off, residual heat from the heater will escape and influence the temperature the thermostat senses. (In other words, the thermostat will temporarily think your room is warmer than it actually is.)
Better yet, install your thermostat one (or more) studs over from the heater
Moving a thermostat out of the same wall cavity as a heater will help performance. Moving your thermostat into an adjacent stud cavity on the same wall is a better option. Why? Well, it won't be directly above the heater, which means that residual heat won't be an issue. (Residual heat isn't really a factor for thermostat placement with our new Apex72 heater, which is shown in the photo above, because it's placed high on the wall.)
Best option: Same room, different inside wall
Installing a wall thermostat on an adjacent wall is the best install option.Putting your thermostat on an inside wall that is adjacent to the one where you installed your heater is better still, according to our Tech Support Manager Dragos Craciun. "To get the best, even temperature in your room, you'd want the thermostat to be on an inside wall that is adjacent to the wall that the heater is on," he said. "So it can only sense the heat from the room and not be offset by being too close to the heater." Remember, this is a good, better and best recommendation system. Sometimes you don't have a lot of choices where you can install a thermostat -- and if you're remodeling a home, that decision was probably already made for you. If you have a choice, why not go for the best option?