Carrier 58UXT Series Operating Instructions Manual Download Page 5

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Air for combustion must not be contaminated by halogen
compounds, which include fluoride, chloride, bromide, and
iodide. These elements are found in aerosol sprays, deter-
gents, bleaches, cleaning solvents, salts, air fresheners, and
other household products.

All fuel-burning equipment must be supplied with air for combus-
tion of fuel. Sufficient air MUST be provided to ensure there will
not be a negative pressure in the equipment room or space. In
addition, a positive seal MUST be made between furnace cabinet
and return-air duct to prevent pulling air from burner area and draft
safeguard opening into the circulating air.

The operation of exhaust fans, kitchen ventilation fans,
clothes dryers, or fireplaces could create a NEGATIVE AIR
PRESSURE CONDITION at the furnace. Make-up air MUST
BE PROVIDED for these devices, in addition to that required
by the furnace.

Combustion and ventilation air requirements are determined by
whether the furnace is located in a CONFINED or UNCONFINED
space.

Step 1—Unconfined Space

An unconfined space has volume of at least 50 cu ft for each 1000
Btuh of total input for all appliances (such as furnaces, clothes
dryers, water heaters, etc.) in the space.

For Example:

If the unconfined space is of unusually tight construction, air for
combustion and ventilation MUST come from either the outdoors
or spaces freely communicating with the outdoors. Combustion
and ventilation openings must be sized the same as for a confined
space as defined below. Return air must not be taken from the
room unless an equal or greater amount of air is supplied to the
room.

Step 2—Confined Space

A confined space is defined as a space whose volume is less than
50 cu ft per 1000 Btuh of total input ratings of all appliances
installed in that space. A confined space MUST have provisions
for supplying air for combustion, ventilation, and dilution of flue
gases using 1 of the following methods. (See Fig. 5 and Table 2.)

NOTE:

In determining free area of an opening, the blocking

effect of louvers, grilles, and screens must be considered. If free
area of louver or grille design is unknown, assume that wood
louvers have a 20 percent free area and metal louvers or grilles
have a 60 percent free area. Screens, when used, must not be
smaller than 1/4-in. mesh. Louvers and grilles must be constructed
so they cannot be closed.

The size of the openings depends upon whether air comes from
outside of the structure or an unconfined space inside the structure.

1. All air from inside the structure requires 2 openings (for

structures not unusually tight):

a. Each opening MUST have at least 1 sq in. of free area per

1000 Btuh of total input for all equipment within the
confined space, but not less than 100 sq in. per opening.
(See Fig. 5 and Table 2.) The minimum dimension of air
openings shall not be less than 3 in.

Table 2—Free Area of Combustion Air Opening*

58UXT

FURNACE

HIGH-FIRE

INPUT

(BTUH)

AIR FROM

UNCONFINED SPACE

OUTDOOR AIR THROUGH

VERTICAL DUCTS

OUTDOOR AIR THROUGH

HORIZONTAL DUCTS