Instruction manual

AIR DUCTS

General Requirements

The duct system should be designed and sized according to

accepted national standards such as those published by: Air

Conditioning Contractors Association (ACCA), Sheet Metal and

Air Conditioning Contractors National Association (SMACNA) or

American Society of Heating, Refrigerating and Air Conditioning

Engineers (ASHRAE) or consult The Air Systems Design

Guidelines reference tables available from your local distributor.

The duct system should be sized to handle the required system

design CFM at the design external static pressure. The furnace

airflow rates are provided in Table 7--Air Delivery--CFM (With

Filter). When a furnace is installed so that the supply ducts carry air

circulated by the furnace to areas outside the space containing the

furnace, the return air shall also be handled by duct(s) sealed to the

furnace casing and terminating outside the space containing the

furnace.

Secure ductwork with proper fasteners for type of ductwork used.

Seal supply-- and return--duct connections to furnace with code

approved tape or duct sealer.

NOTE: Flexible connections should be used between ductwork

and furnace to prevent transmission of vibration.

Ductwork passing through unconditioned space should be

insulated to enhance system performance. When air conditioning is

used, a vapor barrier is recommended.

Maintain a 1--in. (25 mm) clearance from combustible materials to

supply air ductwork for a distance of 36--in. (914 mm) horizontally

from the furnace. See NFPA 90B or local code for further

requirements.

Ductwork Acoustical Treatment

NOTE: Metal duct systems that do not have a 90 degree elbow

and 10 ft. (3 M) of main duct to the first branch take--off may

require internal acoustical lining. As an alternative, fibrous

ductwork may be used if constructed and installed in accordance

with the latest edition of SMACNA construction standard on

fibrous glass ducts. Both acoustical lining and fibrous ductwork

shall comply with NFPA 90B as tested by UL Standard 181 for

Class 1 Rigid air ducts.

NOTE: For horizontal applications, the top most flange may be

bent past 90_ to allow the evaporator coil to hang on the flange

temporarily while the remaining attachment and sealing of the coil

are performed.

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