How do I Size a Direct Vent LP Gas Fireplace for an Area?

Direct vent fireplaces burn propane and natural gas while giving the appearance of a conventional wood fireplace. They need no chimney to expel waste gases, and you need no clearance between their hot surfaces and walls or furniture. Sizing a unit for an existing fireplace means measuring the set fireplace and choosing a model accordingly. Sizing a unit for an area, however, is a different process. You must size your unit based on its heating capacity. Larger areas need more powerful models.

Logs in a gas fireplace appear to burn but do not.

Step 1

Calculate the area in square feet of the location you are heating. If the area is rectangular, measure its length and width, and multiply them together. If the area is irregular, divide it into smaller rectangles and add their areas together.

Step 2

Multiply the area by 12 to calculate your heating requirements, in watts, if this is an uninsulated area. Multiply the area by 9.3 if only the ceiling is insulated. Multiply the area by 7.4 if the ceiling and walls are insulated. Multiply the area by 5.6 if you have a specialized energy efficient home.

For instance, if the area measures 200 square feet, and the ceiling is insulated: 200 x 9.3 = 1,860 watts.

Step 3

Multiply your answer by 3.41 to convert it to British Thermal Units per hour: 1,860 x 3.41 = 6,342 BTUs per hour.

Step 4

Divide your answer by 0.85, which is the average efficiency of a propane heater. 6,342 / 0.85 = approximately 7,500 BTUs per hour. Buy a heater with at least that much heating capacity.

About the Author

Ryan Menezes is a professional writer and blogger. He has a Bachelor of Science in journalism from Boston University and has written for the American Civil Liberties Union, the marketing firm InSegment and the project management service Assembla. He is also a member of Mensa and the American Parliamentary Debate Association.