Sizing Vent-Free Gas Heaters

*Region VI is similar to Region II in temperature
U.S. Department of Energy Heating Regions

Installation of VENT-FREE Gas Products must meet the guidelines of the Local/National Code Ventilation Requirements, as is the case for all gas appliances.

1. Loose Construction - (high heat losses and infiltration rate): little insulation, no storm doors and windows, no vapor barrier, undampered fireplace, and an ACH of about 1.0.

2. Average Construction - (typical heat losses and infiltration rate): insulated, vapor barrier, loose storm doors and windows, dampered fireplace, and an ACH of about 0.5.

3. Tight Construction - (low heat losses and infiltration rate): well insulated, vapor barriers, tight storm doors and windows with weather-stripping, dampered fireplace, and an ACH of about 0.35.

(ACH=Air Changes Per Hour)

1. INFORMATION THAT THE CONSUMER MUST PROVIDE:

a. Measure Room:

Length_______ x Width_______ x Ceiling Height_______ =_______Cubic Ft. This space may be a single room, or it may be connecting rooms or areas.

b. Select the house construction: loose, average, tight.

c. Select the type of heater control system desired: thermostatic or manual operation.

d. Determine the region of the country where the house is located.

HEATER SIZING CALCULATION

1. Find the heater input rate (in Btuh/ft³) from Table-A according to the above information from 1b, 1c and 1d.

2. Multiply this value from Table-A by the volume of space from 1a. This result will provide a minimum heater input (in Btuh) to ensure human comfort under a range of operating conditions.

EXCEPTION:

In heating Region V. if the heater is to be installed in a room which can be isolated from other rooms by doors, find the heater input rate (in Btuh/ft³) from Table-B. Multiply this value from Table-B by the volume of space from 1a. This result will provide a maximum heater input (in Btuh) to ensure acceptable indoor air quality. However, it may not supply enough heat under certain operating conditions. Alternatively, if you increase the ventilation to this isolated room - e.g. by installing a vent to an adjoining room or area at least 40% greater in volume than the isolated space- this exception does not apply.

*Source: Vent-Free Gas Products Alliance,
Vent-Free Gas Products Division of the Gas Appliance Manufacturers Association.