I purchased this insert log set for a fireplace that is open on 3 sides, which is in a large living/dining room. It was purchased for ambiance and heat. Unless you're standing in front of the fireplace you can't feel the heat, even on the high setting. I don't see how this unit can heat a 400 sq ft room. Other than the heat issue I'm pleased with the look of the unit. Nothing to do but plug it in. A very quiet heater, just wished it put out more heat.