Combustion & Ventilation AIR

Provisions for combustion and ventilation air must be in accordance with Section 5.3, Air for Combustion and Ventilation, of the latest edition of the National Fuel Gas Code, ANSI Z223.1; in Canada, the latest edition of CGA Standard B149 Installation Code for Gas Burning Appliances and Equipment; or applicable provisions of the local building codes.

The equipment room must be provided with properly sized openings to assure adequate combustion air and proper ventilation when the unit is installed with conventional venting or sidewall venting.

CAUTION: Under no circumstances should the equipment room be under a negative pressure when atmospheric combustion equipment is installed in the room.

(FIG. 3) COMBUSTION AIR DIRECT FROM OUTSIDE

1.If air is taken directly from outside the building with no duct, provide two permanent openings:

A. Combustion air opening with a minimum free area of one square inch per 4000 Btu input (5.5 cm2 per kW).

This opening must be located within 12” (30 cm) of the bottom of the enclosure.

B.Ventilation air opening with a minimum free area of one square inch per 4000 Btu input (5.5 cm2 per kW). This opening must be located within 12” (30 cm) of the top of the enclosure.

(FIG. 4) COMBUSTION AIR THROUGH DUCTWORK

2.If combustion and ventilation air is taken from the outdoors using a duct to deliver the air to the mechanical room, each of the two openings should be sized based on a minimum free area of one square inch per 2000 Btu input (11 cm2 per kW).

(FIG. 5) COMBUSTION AIR FROM AN

INTERIOR SPACE

3.If air is taken from another interior space, each of the two openings specified above should have a net free area of one square inch for each 1000

EXAMPLE OF

SIZING FOR

COMBUSTION

&VENTILATION AIR OPENINGS (WATER HEATER WITH 2,065,000 Btu/hr INPUT):

When combustion and ventilated air is taken from directly outside the building (FIG. 4), divide the total BTU’s by 4,000. This yields 516.25 sq.in. of “Free Area” without restriction.

(2,065,000 ÷ 4000 =

516.25 sq.in.)

Since the air opening is 50% closed due to screens and louvers, the total opening must be multiplied by 2.

(516.25 sq. in. x 2 =

1,032 sq.in.)

This project requires one Ventilation Air Opening with net “Area” of 1,032 square inches with louver dimensions of 30” x 35” and one

Combustion Air Opening with net “Area” of 1,032 square inches with louver dimensions

of 30” x 35”.

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CW 645, CW 745 specifications

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