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High humidity, especially during cold weather, may be
damaging to buildings because condensation forms on
windows and insde walls.
The combination of a tight energy efficient home with
the use of exhaust fans, fireplaces, clothes dryers, and gas
appliances result in more and more air being drawn from
the house until fresh air may be sucked back into the house
down a furnace flue or fireplace chimney. Carbon monoxide
can be the result. Carbon monoxide (CO) is a colorless,
odorless gas produced when fuel is not burned completely
or when the flame does not receive sufficient oxygen.
Automobiles, charcoal, wood fires and improperly vented or
air(starved coal, oil and gas furnaces or other appliances can
produce carbon monoxide.
BE AWARE OF THESE AIR-STARVATION SIGNALS:
1. Headaches, nausea, dizziness.
2. Excessive humidity shown by heavily frosted windows
or a moist "clammy" sensation.
3. Fireplace smoke fills the room or will not draw.
4. Furnace flue backs up.
AIR REQUIREMENTS
The requirements for providing air for combustion and
ventilation are listed in the National Fuel Gas Code NFPA
54/ANSI Z223.1 (in Canada: CAN/CGA B149). Most homes will
require that outside air be supplied to the heated area by
means of ventilation grilles or ducts connecting directly to
the outside or spaces open to the outdoors such as attic or
crawl space. The only exception is when the furnace area
meets the requirements and definitions for an unconfined
space with adequate air infiltration.
WARNING: Danger of property damage, bodily
injury or loss of life. The furnace and any other fuel-
burning appliances must be provided with enough fresh
air for proper combustion and ventilation of flue gases.
Most homes will require that outside air be supplied into
the heated area.
All air openings and connecting ducts must comply with the
following:
If the furnace is installed in an area with another gas
appliance(s), the total input rating of all appliances must be
considered when determining the free area requirements for
combustion and ventilation air openings.
Ducts must have the same cross-sectional area as the free
area of the openings to which they connect. The minimum
dimension of rectangular air ducts must not be less than 3
inches in length or height.
LOUVERS / GRILLES AND SCREENS COVERING FREE
AREA OPENINGS
If a screen is used to cover the opening(s), it must not be
smaller than 1/4-inch mesh. Use the free area of a louver or grille
to determine the size opening required to provide the free area
specified. If the free area is not known, assume a 20% free area
for wood and a 60% free area for metal louvers or grilles.
EXAMPLE 1
FURNACE LOCATED IN UNCONFINED SPACE.
An unconfined space must have a volume of a minimum
50 cubic feet per 1000 BTU/hr. of total of all appliances in area.
Adjoining rooms may be included only if there are no doors
between the rooms, or if special provisions are made such as
ventilation grilles installed between connecting rooms.
Page 10, Figure 6 shows the minimum area in square feet
based on 8 foot ceiling heights, required for different BTU/hr.
input ratings.
A. If your furnace is in an open area (unconfined space) the
air that leaks through the cracks around doors and
windows may be enough for combustion and ventilation
air. The doors should not fit tight. The cracks around
windows should not be caulked or weather stripped.
To determine if infiltration air is adequate, perform
following checks:
1.
Close all doors and windows. If you have a fireplace, start
a fire and wait until flames are burning vigorously.
2.
Turn on all exhausting devices, such as:: kitchen and
bathroom exhaust fans dryers (gas and electric)
3.
Turn on all vented gas appliances, such as: heating
equipment including any room heaters, water
heater/stoves.
4.
Wait ten (10) minutes for drafts to stabilize.
5.
Check for draft hood spillage at each appliance.
(Hold a lighted match 2 inches from draft opening).
See Figure 4
B. No Spillage
If the match flame pulls toward draft hood ( this indicates
sufficient infiltration air):
1.
Return exhausting devices and appliances to the
condition you found them.
C. Draft Hood Spills
If there is spillage at a draft hood (match goes out or
flame wavers away from draft hood):
1.
Check for plugged flue connectors and chimneys.
Check and repair blockages and test again.
2.
If you have a fireplace, open a window or door near
the fireplace and then check for spillage.
a)
If spillage stops, do not use the fireplace without a
nearby window or door open until you can supply
fresh air by a permanent duct.
3.
If you have kitchen and bathroom exhaust fans, turn
them off and check for spillage.
a)
If spillage stops, do not use exhaust fans until you
can supply fresh air by a permanent duct.
WARNING: Danger of property damage,
bodily injury or loss of life. Draft hood spillage, with
unobstructed vents, indicates that additional air must
be brought into the structure from outside. Keep a
window open (minimum 2 inches) near the appliance
until a permanent air duct is installed.
COUNTERFLOW TOP VENT GAS WALL HEATER
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