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
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 – 65 F | ||
| ||
|
| |
30 – 60 F | ||
|
| |
35 – 65 F | ||
30 – 60 F | ||
|
| |
35 – 65 F | ||
| ||
30 – 60 F | ||
| ||
30 – 65 F | ||
|
|
| CFM Required for a | T of: | ||
Model |
|
|
|
|
35 | 45 | 55 | 65 | |
737 | 574 | 469 | 397 | |
|
|
|
|
|
1053 | 819 | 670 | 567 | |
1433 | 1114 | 912 | 771 | |
1433 | 1114 | 912 | 771 | |
1791 | 1393 | 1140 | 964 | |
1791 | 1393 | 1140 | 964 | |
2107 | 1639 | 1341 | 1134 | |
2107 | 1639 | 1341 | 1134 | |
2107 | 1639 | 1341 | 1134 | |
2423 | 1884 | 1542 | 1305 | |
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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