Fedders F80A dimensions Furnace Sizing, General, Other Considerations

MODEL F80A

FURNACE SIZING

The maximum hourly heat loss for each heated space shall be calculated in accordance with the procedures described in Manual J titled, "Load Calculation" published by the Air Conditioning Contractors of America, or by any other method which is suitable for local conditions, provided the results obtained are in substantial agreement with, and not less than those obtained using the procedure described in their manual.

In Canada, the maximum hourly heat loss for each heated space shall be calculated in accordance with the procedures described in the manuals of the Heating, Refrigeration and Air Conditioning Institute of Canada (HRAI), or by any other method which is suitable for local conditions, provided the results obtained are in substantial agreement with, and not less than those obtained using the procedure described in their manuals.

If the installation is a retrofit application, do not rely on the capacity of the existing heating equipment as a method to size the new furnace. Many of the heat transfer multiples listed in earlier versions of load calculation manuals were much higher than those listed in more recent editions. It is possible that energy saving measures have been completed since the installation of the existing furnace. This might include additional insulation in the attic or walls, the application of sprayed foam insulation, the addition of storm windows and doors, weather stripping, caulking, etc.

Many of the older furnaces were equipped with large belt drive blower systems, operating at low RPMs. If replacing an existing furnace, be sure that the existing ductwork can handle the amount of airflow necessary for a reasonable temperature rise. Most older gas furnaces operated with a system temperature rise of 70 - 100°F. This series furnace has been designed for operation with a system temperature rise (DT) of 35 - 65°F or 30 – 60°F depending on which model is being installed. See Table 1A below. If the furnace selected has an identical output capacity as the original furnace, a substantial increase in system airflow will be required. See Table 1B below.

TABLE 1A	TABLE 1B
FURNACE TEMPERATURE RISE	TYPICAL AIR FLOW

The equal friction chart, as published by ASHRAE and HRAI, is the basis for the various air duct calculators available through heating supply companies.

NOTE: The return air system is equally as important as the supply air system. An undersized return air system will prevent sufficient quantities of air from reaching the supply air system, properly sized or otherwise, and will consequently reduce the service life of the furnace and its components.

LOCATION of UNIT

GENERAL:

1.The furnace is not weatherized. Select a dry indoor location.

2.Select a location where the furnace venting can be routed between the furnace and the chimney or B-Vent with a minimum of lengths and fittings. Be sure to check that the proposed routing will meet code requirements with respect to minimum clearances.

3.Select a location as near as possible to the existing or proposed duct system.

4.The furnace location must permit access for servicing, and be within the clearance to combustibles guidelines as marked on the appliance rating plate.

5.The furnace should be installed on a firm base when installed in the upflow position. This is typically a concrete floor if installing the furnace in a basement.

6.If the furnace is being installed so that the return air will enter through the bottom, the perimeter of the furnace must be properly supported.

7.When installed in the horizontal position, the furnace may be supported from the bottom, or suspended.

8.When installed in the down flow position on a combustible floor, subbase kit #30476 is required (contact manufacturer for availability).

OTHER CONSIDERATIONS:

•	This furnace is not to be used for temporary heating of
	buildings or structures under construction.
•	If this furnace is to be used with air conditioning and is
	to be installed in an area over a finished ceiling or

Furnace Model	Tem perature
	Rise
35-2
50-3	35 – 65 F
70-3
70-4	30 – 60 F
85-3	35 – 65 F
85-4	30 – 60 F
100-3	35 – 65 F
100-4
100-5	30 – 60 F
115-5
135-5	30 – 65 F

	CFM Required for a			T of:
Model
	35	45	55	65
35-2	737	574	469	397
50-3	1053	819	670	567
70-3	1433	1114	912	771
70-4	1433	1114	912	771
85-3	1791	1393	1140	964
85-4	1791	1393	1140	964
100-3	2107	1639	1341	1134
100-4	2107	1639	1341	1134
100-5	2107	1639	1341	1134
115-5	2423	1884	1542	1305
135-5	2844	2212	1810	1532

living area, install a field fabricated auxiliary drain pan

under the furnace to protect that area from accidental

condensate spills. The auxiliary pan should be large

enough to collect accidentally spilled condensate from

the air conditioning evaporator coil assembly if

applicable. Follow local codes.

• These furnaces are approved for installation in attics,

alcoves, utility rooms, closets and crawlspaces. If this

furnace is to be installed in a utility room, be sure that

it is located in such a way as to allow access for

servicing or the removal of any other appliance, (hot

water heater, for example).

• If the furnace is to be installed in a garage, the burners

must be a minimum of 18 inches (460 mm) above the

floor.

Existing ductwork should be assessed for its air handling capabilities. For residential applications, the recommended air velocity of a supply air trunk duct is 700 feet per minute (fpm), and should not exceed 900 fpm. The recommended air velocity of a supply air branch run is 600 fpm, and should not exceed 900 fpm. These values are slightly lower for flexible ducting. The recommended air velocity of a return air trunk duct is 600 fpm, and should not exceed 700 fpm. The recommended and maximum air velocity of a return air branch is 600 fpm.

•	If the furnace is to be installed in a commercial (repair)
	garage, the burners must be a minimum of 4.5 feet
	(1375 mm) above the floor.
•	The furnace must be protected from physical damage
	by metal barriers or other acceptable means.

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