Filter
Top Products
111826-05
For more information, visit www.desatech.com
5
5
40,000
33,000
73,000
Unusually tight construction is defined as construction
where:
a. walls and ceilings exposed to the outside atmosphere
have a continuous water vapor retarder with a rating
of one perm (6 x 10
-11
kg per pa-sec-m
2
) or less with
openings gasketed or sealed and
b. weather stripping has been added on openable win-
dows and doors and
c. caulking or sealants are applied to areas such as
joints around window and door frames, between sole
plates and floors, between wall-ceiling joints, between
wall panels, at penetrations for plumbing, electrical,
and gas lines, and at other openings.
If your home meets all of the three criteria above, you
must provide additional fresh air. See Ventilation Air
From Outdoors, page 6.
If your home does not meet all of the three criteria above,
proceed to Determining Fresh-Air Flow For Heater Lo-
cation, below.
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/NFPA 54 defines a
confined space as a space whose volume is less than 50 cubic feet
per 1,000 Btu per hour (4.8 m
3
per kw) of the aggregate input rating
of all appliances installed in that space and an unconfined space as
a space whose volume is not less than 50 cubic feet per 1,000 Btu
per hour (4.8 m
3
per kw) of the aggregate input rating of all appli-
ances installed in that space. Rooms communicating directly with
the space in which the appliances are installed*, through openings
not furnished with doors, are considered a part of the unconfined
space.
* Adjoining rooms are communicating only if there are doorless
passageways or ventilation grills between them.
DETERMINING FRESH-AIR FLOW FOR
HEATER LOCATION
Determining if You Have a Confined or Unconfined
Space
Use this work sheet to determine if you have a confined or unconfined
space.
Space: Includes the room in which you will install heater plus any ad-
joining rooms with doorless passageways or ventilation grills between
the rooms.
1. Determine the volume of the space (length x width x height).
Length x Width x Height = ____________cu. ft. (volume of space)
Example: Space size 20 ft. (length) x 16 ft. (width) x 8 ft. (ceiling
height) = 2560 cu. ft. (volume of space)
AIR FOR COMBUSTION AND
VENTILATION
Continued
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 construc-
tion, provide adequate combustion and ventilation
air by one of the methods described in the National
Fuel Gas Code, ANSI Z223.1/NFPA 54 Section 5.3 or
applicable local codes.
If additional ventilation to adjoining room is supplied with grills or open-
ings, add the volume of these rooms to the total volume of the space.
2. Multiply the space volume by 20 to determine the maximum Btu/Hr
the space can support.
____________(volume of space) x 20 = (Maximum Btu/Hr the space
can support)
Example: 2560 cu. ft. (volume of space) x 20 = 51,200 (maximum
Btu/Hr the space can support)
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free heater _____________ Btu/Hr
Gas water heater* _____________ Btu/Hr
Gas furnace _____________ Btu/Hr
Vented gas heater _____________ Btu/Hr
Gas fireplace logs _____________ Btu/Hr
Other gas appliances* + _____________ Btu/Hr
Total = _____________ Btu/Hr
* Do not include direct-vent gas appliances. Direct-vent draws com-
bustion air from the outdoors and vents to the outdoors.
Example:
Gas water heater _____________ Btu/Hr
Vent-free heater + _____________ Btu/Hr
Total = _____________ Btu/Hr
4. Compare the maximum Btu/Hr the space can support with the actual
amount of Btu/Hr used.
____________________Btu/Hr (maximum the space can support)
____________________Btu/Hr (actual amount of Btu/Hr used)
Example: 51,200 Btu/Hr (maximum the space can support)
73,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the above 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:
A. Rework worksheet, adding the space of an adjoining room. If the extra
space provides an unconfined space, remove door to adjoining room or
add ventilation grills between rooms. See Ventilation Air From Inside
Building, page 6.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors,
page 6.
C. Install a lower Btu/Hr heater, if lower Btu/Hr size makes room uncon-
fined.
If the actual Btu/Hr used is less than the maximum Btu/Hr the space can sup-
port, the space is an unconfined space. You will need no additional fresh air
ventilation.
AIR FOR COMBUSTION AND VENTILATION
Providing Adequate Ventilation (Cont.)
Determining Fresh-Air Flow for Heater Location