9
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Use this worksheet to determine if you have a confined or unconfined space. Space: Includes the room in
which you will install heater plus any adjoining rooms with door less passageways or ventilation grills
between the rooms.
1. Determine the Volume of space in cubic feet
Length X Width X Height = ___________________ cu. Ft.
(Including adjoining rooms with door less passageways or ventilation grills between rooms)
Example: 24’ (L) X 16’ (W) 8’ (H) = 3,072 cu. Ft.
2. Multiply the volume of space by 20 BTU/Hr. to determine the maximum BTU/Hr. the space can
support.
Example: 3.072 cu. Ft. X 20 BTU/Hr. = 61,440 BTU/Hr.
(Maximum BTU/Hr. the room can support)
3. Add the BTU/Hr. of all the fuel burning appliances in the space
Vent Free Heater _________________BTU/Hr.
Gas Appliance #1_________________BTU/Hr.
Gas Appliance #2_________________BTU/Hr.
Example: Vent Free Heater
26,000 BTU/Hr.
Gas Appliance #1
35,000 BTU/Hr.
Total
61,000 BTU/Hr.
The space in the prior example is a confined space because the actual BTU/hr used is more than the
maximum BTU/hr the space can support.
You must provide additional fresh air. Your options are as follows:
Rework worksheet, adding the space of an adjoining room. If the extra space provides an unconfined
space:
a) Remove door to adjoining room or add ventilation grills betwe
en rooms. See “Ventilation Air
from Inside Building
” on next page.
b) Vent room directly to the outdoors. See the following
“Ventilation Air from Outdoors” for details.
c) Install a lower BTU/hr heater if lower BTU/hr size makes room unconfined. If the actual BTU/hr
used is less than the maximum BTU/hr the space can support, the space is an unconfined
space. You will need no additional fresh air ventilation.
WARNING:
If the area in which the heater may be operated is smaller than that defined as an
unconfined space, or if the building is of unusually tight construction, provide adequate combustion
and ventilation air by one of the methods described in the National Fuel Gas Code, ANSI Z223.1/NFPA
54, Air for Combustion and Ventilation, or applicable local codes.
