Sizing Guidelines for Vent-Free Gas Products PDF Print E-mail

Selecting the right heat input (BTU/hr) for your home is easy to do by following these easy steps:

  1. Locate the region (I, II, III, IV, V or VI) where you live on the Heating Region Map.

    Heating Region Map

  2. Choose the location in your home where you would like to install the product.
  3. Close all the doors to rooms that can be reached from the location where your product will be installed. This will be the space that your vent-free gas appliance will heat.
  4. Calculate the volume of this space by multiplying the length in feet by the width in feet by the height in feet. With multiple rooms that are connected and not separated by doors, you will have to calculate the volume of each room and add the results for all rooms to arrive at the total volume.
  5. Multiply the total volume by the number below that corresponds to your heating region (determined in step # 1):

    Region I – 1.85
    Region II – 2.20
    Region III – 2.60
    Region IV – 3.15
    Region V – 3.85
    Region VI – 2.20

The result will be the minimum heat input (BTU/hr) of the product that you should consider.


a) In bathrooms, select a product equal to or less than 6,000 BTU/hr.
b) In bedrooms, select a product equal to or less than 10,000 BTU/hr.
c) In single rooms in Region V, multiply the room's volume by 3.20. The result is the maximum heat input (BTU/hr) of the product that you should consider.

Here's a sample calculation:

Dick and Jane live in Columbus, Ohio. Looking at the Heating Region Map, they determine that Columbus is in Region IV.

They choose a location in their great room to install the product.

After closing all the doors leading into the great room, they determine that the space to be heated includes the great room, dining area, kitchen and hallway.

They measure the spaces to be heated to arrive at the total volume (length x width x height):

  Length x Width x Height  
Great Room 16' x 14' x 9' = 2,016
Dining Area 12' x 14' x 9' = 1,512
Kitchen 12' x 11' x 9' = 1,888
Hallway 12' x 4' x 9' = 432
  Total Volume = 5,148

Then Dick and Jane multiply the total volume by 3.15 (for Region IV), and learn they should select a product with a minimum input of 16,216 BTU/hr.

After browsing all the choices available at their local hearth shop and home center stores, they decide on a 26,000 BTU/hr fireplace system having a minimum input of 14,000 BTU/hr.

Note: These guidelines apply to average house construction. If your house is built very tight, it won't need as much heat input. Conversely, if your house is loose – typical of old construction – it'll need a little more heat input.