When looking for a gas-fired unit, be sure to look for the "BTU" rating. A BTU (British Thermal Unit) is a measure of heat energy, and as a general rule of thumb, 35,000 BTUs will provide sufficient heating for about 1,000 square feet. By no means is this an absolute measurement, as windows, doors, ceiling height, and other factors come into play, but it is a good starting point. We would also recommend checking out the Direct Vent Fireplace Buyer's Guide written by our certified technicians!