TABLE 9: Equivalent Length of Fittings
Fitting | Equivalent Length |
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|
2" 90º sweep elbow | 5 feet of 2" pipe |
2" 45º sweep elbow | |
2" 90º standard elbow | 10 feet of 2" pipe |
2" 45º standard elbow | 5 feet of 2" pipe |
3" 90º sweep elbow | 5 feet of 3" pipe |
3" 45º sweep elbow | |
3" 90º standard elbow | 10 feet of 3" pipe |
3" 45º standard elbow | 5 feet of 3" pipe |
2" corrugated connector | 10 feet of 2" pipe |
3" corrugated connector | 10 feet of 3" pipe |
Example:
An 80,000 BTUH furnace requires 32 feet of pipe and four 90º elbows. Using 2" pipe and standard elbows, the total equivalent length will be:
32 feet of 2" pipe = | 32 equivalent feet |
4 - 90º standard 2" elbows = (4x10) = | 40 equivalent feet |
Total = | 72 equivalent feet of 2" pipe |
This exceeds the 65 foot maximum equivalent length of 2" pipe allowed for that model and is thus not acceptable.
By using sweep elbows, the total equivalent length will be:
32 feet of 2" pipe = | 32 equivalent feet |
4 - 90º standard 2" elbows = (4x5) = | 20 equivalent feet |
Total = | 52 equivalent feet of 2" pipe |
This is less than the 65 foot maximum equivalent length of 2" pipe allowed for that model and is thus acceptable.
Alternatively, using 3" pipe and standard elbows, the total equivalent length will be:
32 feet of 3" pipe = | 32 equivalent feet |
4 - 90º standard 2" elbows = (4x5) = | 40 equivalent feet |
Total = | 72 equivalent feet of 3" pipe |
This is less than the 90 foot maximum equivalent length of 3" pipe allowed for that model and is thus acceptable.
TABLE 10: Combustion Air Intake and Vent Connection Size at Furnace (All Models)
FURNACE VENT CONNECTION SIZES
Furnace Input | 40 - 100 MBH | 120 - 130 MBH | |
(17.5 - 29.3 kW) | (35.2 - 39.6 kW) | ||
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| |
Intake Pipe Size | 2” (5.1 cm) | 3” (7.6 cm) | |
Vent Pipe Size | 2” (5.1 cm) | 2” (5.1 cm) |
*. Vent pipe size must be increased to 3” diameter after connection to furnace on this model.
Accessory concentric vent / intake termination kits 1CT0302 and 1CT0303 are available and approved for use with these furnaces. Horizontal sidewall vent terminations kits 1HT0901 & 1HT0902 are also approved for use with these furnaces.
Furnace vent pipe connections are sized for 2” (5.1 cm). pipe. Any pipe size change must be made outside the furnace casing in a ver- tical pipe section to allow proper drainage of condensate. An offset using two 45º (degree) elbows will be required for plenum clear- ance when the vent is increased to 3” (7.6 cm).
COMBUSTION AIR AND VENT PIPING ASSEMBLY
The final assembly procedure for the combustion air and vent piping is as follows:
1.Cut piping to the proper length beginning at the furnace.
2.Deburr the piping inside and outside.
3.Chamfer (bevel) the outer edges of the piping.
4.
5.
a.Sealed combustion air systems from the furnace to the out- side termination.
b.Ventilated combustion air systems from the furnace to the attic or crawl space termination.
Solvent cements are flammable and must be used in
6.Disassemble the combustion air and vent piping, apply cement primer and the cement per the manufactures instructions. Primer and cement must conform to ASTM D2564 for PVC, or ASTM D2235 for ABS piping.
7.All joints must provide a permanent airtight and watertight seal.
8.Support the combustion air and vent piping such that it is angled a minimum of 1/4” per foot (21 mm/m) so that condensate will flow back towards the furnace. Piping should be supported with pipe hangers to prevent sagging.
9.Seal around the openings where the combustion air and / or vent piping pass through the roof or sidewalls.
COMBUSTION AIR / VENTING
The vent must be installed with the minimum required clearances, and must comply with local codes and requirements.
22 | Johnson Controls Unitary Products |
