4. For All Horizontal applications:
Return air can only be connected to bottom opening of furnace. (See Fig. 2.) A common return air plenum is required for proper auxiliary
limit switch operation.
WARNING: UNIT DAMAGE AND FIRE HAZARD
Failure to follow this warning could result in unit damage, fire, personal injury or death.
DO NOT use the side or back of the furnace for return-air duct connections in the horizontal position, as limit cycling will occur.
5. Apply 2 factory-supplied foam strips to the back of each furnace. Locate strips equal distance from top and bottom as shown in Fig. 5. Trim
off excess material.
6. Determine which side of furnace will be used to route external extension harness. Remove 7/8-in. diameter accessory hole knockouts in
blower compartment side selected to attach harness to. (See Fig. 3.)
7. Position furnaces back-to-back on attic platform or suspended supports. Adjust and shim each furnace to align both furnaces. Follow all
clearance to combustible material.
8. If furnaces are installed closer than 12 inches above a deck made from combustible material, provide roll-out protection as shown in the
furnace installation instructions. The bottom closure pan may be used for this purpose.
NOTE:
DO NOT lay furnace down flat on the side that external extension harness is installed. Raise furnace up a minimum of 1½ inches above
deck so harness does not rub on casing or deck.
9. Drill two 1/8-in. holes, approximately 1 in. below discharge flange, from inside top of discharge opening and through both furnaces. (See
Fig. 6.) Drill two 1/8-in. holes, approximately 1 in. below return air flange, from inside top of return air opening and through both furnaces.
(Use Fig. 6 as an example)
10. Drive 1 factory-supplied No. 6 X 3/4-in. LG screw through each hole and tighten until furnaces are secure and foam strips have sealed gap
between furnaces.
11. Connect return- and supply-air ducts to furnaces. Seal duct connections to prevent air leakage.
12. Move 115-v junction box JB in either furnace from left-hand side to right-hand side if required. Refer to furnace installation instructions
for complete details.
13. Go to PROCEDURE 2A for Single Stage Furnaces or PROCEDURE 2B for Two Stage Furnaces.
D.
Horizontal, Stacked Together
When twinning furnaces in the horizontal position, consideration must be made to the type of building construction. Attic floors should be
constructed to support normal live and dead loads of the furnaces and the person(s) servicing them.
Trusses, wood and metal are engineered for specific applications, and may not support the weight of two (2) furnaces suspended from the top
chords or the bottom chords of the trusses. Long horizontals spans may flex or sag, resulting in damage to the building. Contact the truss
manufacturer for additional design and engineering assistance.
Do not suspend furnaces with straps or suspend furnaces from roof decking.
For attic installations on a platform (See Fig 9a):
1. Construct a platform from ¾
″
(nominal plywood), extending out 30 inches from the front of each furnace.
2. Maintain all clearances to combustibles per the furnace Installation, Start-up and Operating Instructions.
3. Follow all additional building codes.
4. Long truss spans may require additional support along the bottom chord of the truss. Consult the truss manufacturer’s guidelines for
engineering assistance.
5. Long rafter or attic joist spans may require additional support along the bottom of the rafter or joist. Consult local or regional building codes
for design and loading requirements.
For suspended installations (See Fig 9b. Not recommended for wood trusses unless approved by the truss manufacturer or other approved
engineering methods):
1. Furnaces may be suspended using two (2) pieces of 1 ½” x 1 ½” x ¼” thick cold rolled angle iron underneath the furnaces and four (4)
3/8
″
diameter threaded rods.
2. Allow for at least nine (9) inches in front of each door for door removal.
3. Each piece of angle iron must be secured to the bottom of each furnace with at least two (2) #8 x ¾
″
sheet metal screws.
4. Maintain all clearances to combustibles per the furnace Installation, Start-up and Operating Instructions.
5. Unistrut or similar material may be used, provided that the furnaces do not sag in the middle or bend or twist at the support ends. The support
material must be secured to the bottom of each furnace in a manner similar to securing angle iron to the furnace.
Refer to Fig. 3 and Table 2 for appearance and dimensional drawing of twinned furnaces and their connection locations.
1. Select 2 identical heating and airflow furnaces. (See Table 2.)
2. Remove outer door and blower access door.
3. Remove bottom closure panels from both furnaces. (See Fig. 4.)
a. Lay furnaces on back or sides.
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