Style selections SSD24TR - Determining if You Have a Confined or Unconfined Space; Determine the Volume of the Space; Determining Fresh-Air Flow for Heater Location; Unusually Tight Construction

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Example:
Gas water heater 40,000 BTU/hr
Vent-free heater + 31,500 BTU/hr
Total = 71,500 BTU/hr
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DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Conned or Unconned Space
Use this worksheet to determine if you have a conned or unconned space.
Space: Includes the room in which you will install heater plus any adjoining rooms with
doorless passageways or ventilation grills between the rooms.
1
. Determine the volume of the space
Length × Width × Height = cu. ft. (volume of space)
Example: Space size 20 ft. (length) × 16 ft. (width)× 8 ft. (ceiling height)= 2560 cu. ft.
(volume of space)
If additional ventilation to adjoining room is supplied with grills or openings, add the
volume of these rooms to the total volume of the space.
2. Divide the space volume by 50 cubic feet to determine the maximum BTU/hr the space
can support.
(volume of space) ÷ 50 cu. ft.= (Maximum BTU/hr the space can support)
3.
Add the BTU/hr of all fuel burning appliances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas heater logs
Other gas appliances* +
Total =
*Do not include direct-vent gas appliances. Direct-vent draws combustion air from the
outdoors and vents to the outdoors.
Unusually Tight Construction
The air that leaks around doors and windows may provide enough fresh air for combustion
and ventilation. However, in buildings of unusually tight construction, you must provide
additional fresh air.
Unusually tight construction is dened as construction where:
walls and ceilings exposed to the outside atmosphere have a continuous water vapor
r
etarder with a rating of one perm (6×10
-11
kg per pa-sec-m
2
) or less with openings
gasketed or sealed and
Weather stripping has been added on openable windows and on doors and
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”. If your home does not meet all of the three
criteria above, proceed to “Determining Fresh-Air Flow For Heater Location”.
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