Carrier 58 User Manual

Number One AirConditbninq Maker

Division o1 Carrier Corporation

Carrier Parkway • Syracuse NY 13221

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U-

Procedures for Gas-Fired Furnaces

INTRODUCTION

The Need for Adequate Combustion Air —

Modern construction methods involve greater use of

insulation, improved vapor barriers and weather

stripping, with the result that both apartments and single-family residences generally are much tighter structurally than they have been in the past. Combustion air supply for gas-fired equipment can be affected by these construction conditions, be cause infiltration that existed in the past may not now be adequate. Extensive use of kitchen and bath room exhaust fans, and even fireplaces, aggravates the situation.

Today’s building practices invalidate the old rule of thumb of “one air change by infiltration.” Reli ance on this practice can result in combustion air

starvation if proper combustion air is not provided. In fact, recent field investigations, particularly with

closet installation of gas-fired furnaces, indicate the

need for positive provision for combustion air and for a better understanding of application guidelines that relate to today’s conditions.

These instructions cover minimum combustion air requirements and venting practices, reflect current conditions found in the field, and conform to existing national standards and safety codes. In

some instances, these instructions exceed certain local codes and ordinances, especially those that may not have kept pace with the changing resi dential construction practices. Carrier requires these

standard procedures as a minimum for a safe installation.

CAUTION: Do not obstruct openings in front of the furnace or in the top on each side of the vent pipe. These provide air for combustion and ventilation. Never store anything on or in con tact with the furnace such as;

Spray or aerosol cans, rags, brooms, dust mops, vacuum cleaners, or other cleaning tools.

Soap powders, bleaches, waxes or other clean ing compounds, plastic or plastic containers, gasoline, kerosene, cigarette lighter fluid, dry cleaning fluids, or other volatile fluids.

Paint ihinners and other painting compounds,

paper bags or other paper products.

Installation Procedures — The following recom

mendations apply to the installation and operation

of gas furnaces and piping systems for natural and LP gases. Use these procedures in conjunction with

the specific furnace installation instructions.

Refer also to the regulations of the serving gas

supplier and the local building, heating, plumbing

or other codes in effect in the area in which the

installation is made.

Portions of the following have been adopted in

part from the “National Fuel Gas Code” (NFPA

No. 54-1980 or ANSI Z223.I-I980) copyrighted by

the National Fire Protection Association and

American Gas Association. For further details, con sult this publication or current edition available from NFPA, 470 Atlantic Avenue, Boston, MA 02210, or American Gas Association, 1515 Wilson

Boulevard, Arlington, VA 22209.

These instructions contain the following sections:

Page

Inspection

...............................................................

Location and Air for Combustion

and Ventilation.................................................. I

Gas Piping.............................................................. 4

Venting..................................................................... 4

Electrical.................................................................. 5

Start-Up, Adjustment, and Safety Check .... 5

Furnace Location with Respect to

Cooling Equipment........................................... 7

Special Locations

...

................................................

INSPECTION

Check the available power supply to be sure that

it meets the specifications on the wiring diagram and all motors in the furnace.

Check the available gas supply to see that it con

forms to the gas specification on the AGA rating

plate.

LOCATION AND AIR FOR COMBUSTION

AND VENTILATION

Locate the furnace close to the chimney and as near the center of the air distribution system as possible. Provide ample space for servicing and cleaning. Always comply with minimum fire protec

tion clearances shown on the unit rating plate. Do

not install directly on carpeting, tile or any com

bustible material other than wood flooring. If base

for combustible floor is required, obtain from

Carrier distributor or dealer.

The draft hood relief air supply must be in the same atmospheric pressure zone as the combustion air inlet supply to the furnace.

When a furnace is installed so that supply ducts carry air to areas outside the space containing the furnace, the return air must also be handled by duct(s) sealed to the furnace casing and terminating outside the space containing the furnace.

All fuel-burning equipment must be supplied with air, which enters into the combustion process and is then vented to the outdoors. Sufficient air must enter the equipment room to replace that drawn up the vent stack. Replacement air must be provided by means of ducts from the outside to the equipment location or conditioned space. Under all conditions, enough air must be provided to ensure there will not be a negative pressure condition within the equip ment room or space. A positive seal

must be made between the furnace base and platform or return-air duct connections. Even a “slight” leak can create a negative pressure condition in a confined closet or basement, and affect combustion. If necessary, seal the furnace base to floor opening with fiberglass or other approved material. Furnaces with sideconnected returns should utilize an accessory bottom closure, properly sealed.

Complete combustion requires approximately

10 cu ft of air for every 1000 Btu of gas fuel. In addi tion, approximately 10 more cu ft of air is required for draft hood dilution, and 10 more for ventilation of the furnace enclosure. Thus, for eaeh 1000 Btu of gas consumed, a total of 30 cu ft of air must be sup plied. For a 100,000 Btuh gas furnace, this equals 3000 cu ft of air per hour (100 x 30) or 50 cu ft of air per minute (3000 60). In the past, the infiltration of outside air assumed in heat loss calculations (one air change per hour) was assumed to be sufficient.

However, current eonstruction methods, utilizing more insulation and vapor barriers, tighter fitting and gasketed doors and windows or weatherstrip ping, and the presence of fuel-burning fireplaces and

mechanical exhaust fans from kitchens, laundries, and baths require the positive introduction of outside air.

CAUTION; Combustion air must come from a source that is not contaminated by halogens, which include fluorides, chlorides, bromides, and iodides. These elements are found in aerosol sprays, detergents, bleaches, cleaning solvents, salts, air fresheners, and other household prod

ucts. Vapors from these products are highly corrosive to gas-fired furnaces, in even ex tremely low concentrations—as low as 1 / 2 part per million. When such contaminants are pre

sent, outside air mttft be ducted separately to the furnace room.

Operation of exhaust fans, kitchen ventilation

systems, clothes dryers, or fireplaces may create

conditions requiring special attention to avoid un satisfactory operation of installed gas furnaces. Commonly used exhaust fans and range hoods handle anywhere from 60 to 300 cfm (or more) and gas or electric clothes dryers may remove more air. With multiple use of such appliances common in both old and new homes and apartments, special provisions for positive introduction of outside air are mandatory. This air requirement is several times that required by the furnace, and must be replaced, in addition to the air required by the furnace.

The requirements for combustion and ventilation

air depend upon whether the furnace is located in a

confined or unconfined space. An unconfined space

is defined as a space with a volume not less than

50 cu ft/1000 Btuh of the total input rating of all appliances installed in that space. Rooms communi cating directly with the space in which the appliances are installed, thru openings not furnished with doors, are considered a part of the unconfined space.

A confined space is defined as a space with a vol

ume less than 50 cu ft/1000 Btuh of the total input

ratings of all appliances installed in that space.

Furnaces in Confined Spaces (Typical Furnace

Closet)

ALL AIR FROM INSIDE BUILDINGS:

The confined space shall be provided with 2 per manent openings, one beginning within 12 in. of the top and one beginning within 12 in. of the bottom of the enclosure. Each opening shall have a minimum free area of 1 sq in. per 1000 Btuh of the total input rating of all equipment in the enclosure, but not have less than 100 sq inches. The openings must freely communicate with interior areas served by the furnace, either thru permanent openings or louvered doors.

In addition, if building is of unusually tight con struction, provide one permanent opening directly communicating with outdoors. This opening shall have a minimum free area of 1 sq in. per 5000 Btuh of total input rating of all equipment in the en closure. Ducts shall be used to convey makeup air and shall be of the same cross-sectional area as the

free areas of the openings to which they connect. This duct should be connected to the cold air return

of the heating system. The minimum dimension of

the rectangular air ducts should not be less than

3 inches. See Fig. 1.

If the furnace is instafled on a raised platform

to provide a return air plenum, and return air is taken directly from the hallway or space adjacent to the furnace, all air for combustion must come from outdoors, as prescribed below.

ALL AIR FROM OUTDOORS:

The confined space shall be provided with 2 per manent openings, one commencing within 12 in. of the top and one commencing within 12 in. of the

RETURN OR SUPPLY AIR

VENT TO ROOF

I I

I I I I I I

12 IN MAX

D_L

■= I so IN.

~ PER 1000

BTUH*

INTERIOR HEATED

SPACE

-6IN MIN

(FRONT)

ISO IN

# per 1000 HTBTUH*

I so IN. PER 2000 BTUH ^

RETURN OR SUPPLY AIR

*MINIMUM OPENING SIZE IS 100 SO IN

-d

*-12 IN MAX

MAKEUP AIR ISO IN

-PER 5000 BTUH FROM OUTSIDE (RETURN

AIR ONLY)

Fig. 1 — Upflow or Counterflow, Using Air

from Inside Building

bottom of the enclosure. These openings shall com municate directly, or by ducts, with outdoors. See Fig. 2.

a. When communicating with the outdoors thru

horizontal ducts, each opening shall have mini mum free area of 1 sq in. per 2000 Btuh of total input rating for all equipment in the enclosure. If vertical ducts or openings with louvers and grilles are used, each opening or duct shall have a minimum free area of 1 sq in. per 4000 Btuh of the total rated input of all equipment in the enclosure.

b. When ducts are used, they shall be of the

same cross-sectional area as the free area of the openings to which they connect. The mini

mum dimension of rectangular air ducts shall not be less than 3 inches.

Furnaces in Unconfined Spaces (Basements, Large Equipment Rooms, etc.) — If the uncon

fined space is within a building of unusually tight construction, air for combustion, ventilation, and dilution of flue gases shall be obtained from out doors or from spaces freely communicating with the outdoors. A permanent opening, or openings, having a total free area of not less than 1 sq. in. per 5000 Btuh of total input rating for all equipment shall be provided. A duct may be used to convey

USE ANY OF THE FOLLOWING COMBINATIONS OF OPENINGS: ABB CSD D&E

*MINIMUM OPENING SIZE IS 100 SO IN

Fig. 2 — Upflow or Counterflow. Using Air

from Outside Building

makeup air from the outdoors and shall be of the same cross-sectional area as the free area of the openings to which it connects. The duct may be con nected to the eold air return of the heating system only if it connects directly to outside air. The minimum dimension of rectangular air ducts shall be not less than 3 inches.

CAUTION: Return air must not be taken from the room, unless an equal or greater amount of air is supplied to the room. All duct connections to the furnace must be airtight to avoid causing

a “negative” pressure condition within the room.

Louvers and Grilles — In calculating the free area,

consideration shall be given to the blocking effect of

louvers, grilles, or screens protecting openings. Screens used must not be smaller than I / 4-in. mesh. If the free area thru a design of louver or grille is known, it should be used in calculating the size opening required to provide the free area specified.

If the design and free area is not known, assume that wood louvers will have 20- to 25-percent free area and metal louvers and grilles will have 60- to 75percent free area. Louvers and grilles that provide combustion and dilution air must be constructed so

they cannot be closed.

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