FMI VENT FREE UNIVERSAL MASONRY FIREBOX MM39/44/49VF - Manual (Page 12)

11
Unconfined Space
An unconfined space has a minimum total air volume of
50 cu.ft. (cubic feet) for each 1,000 Btu/Hr input rating of all
appliances in the total space (cu.ft. = length x width x height
of space). Include adjoining rooms only if there are doorless
passageways or ventilation grills between the rooms. If the Btu
per 50 cu.ft. is less than 1,000 Btu/Hr, then fresh air will be
provided by the natural air flow into the house.
Confined Space
A confined space has an air volume of less than 50 cu.ft. for
each 1,000 Btu/Hr input rating of all appliances in the space (cu.
ft. = length x width x height of space). Include adjoining rooms
only if there are door less passageways or ventilation grills
between the rooms.
Determining Total Air Volume
Use this work sheet to determine if you have a confined
or unconfined space. The space to be considered includes not
only the room in which you will install the fireplace but also any
adjoining rooms with ventilation grills between them or door
less passageways.
1. Determine the total volume of your space
L x W x H = _______ cu.ft.
Example: Space size = 20 ft. long x 20 ft. wide x 8 ft. high
(ceiling height) = 3,200 cu.ft.
If adjoining 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 cu.ft. to determine the
maximum Btu/Hr the space can support.
_______ cu.ft. (volume of space)
50 cu ft. = (Maximum Btu/Hr the space can support)
Example: 3200 cu ft. (Volume of space) / 50 cu. Ft. = 64.0 or
64,000 (maximum Btu/Hr the space can support.)
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free fireplace _______ 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
Example: Gas water heater 40,000 Btu/hr
Vent-free fireplace +36,000 Btu/hr
Total = 76,000 Btu/hr
* Do not include direct-vented gas appliances. Direct vent draws
combustion air from the outdoors and vents to the outdoors.
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:
64,000 Btu/Hr (maximum the space can support)
76,000 Btu/Hr (actual amount of Btu/Hr used)
The space in the previous example was a confined space
because the actual Btu/Hr used was more than the maximum
Btu/Hr the space could support. If you find you have a Confined
Space, you must provide additional fresh air. Your options are
as follows:
a) Re-work worksheet, adding the space of an adjoining room
that may not have qualified for the extra volume. If the extra
space provides enough volume to convert the area to an
unconfined space, remove door to adjoining room or add
ventilation grills between rooms.
b) Vent room directly to the outdoors.
c) Install a lower Btu/Hr gas log (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, provide
adequate combustion and ventilation air by one of the methods
described in the National Fuel Gas Code, ANSI Z223.1 Section
5.3 or applicable local codes.
Local codes may have stricter definitions for confined space
and/or for unusually tight construction. Installing our optional
outside air kit may allow the space to be classified as not being
unusually tight or being an unconfined space. Check you local
codes.
IMPORTANT: Do not provide openings for inlet or outlet air
into an attic if the attic has a thermostat-controlled power vent.
Heated air entering the attic will activate the power vent.