440 01 4801 00
19
Specifications subject to change without notice.
Not all horizontal furnaces are approved for side return air
connections See Fig. 23. Where required by code, seal bottom
closure to furnace with tape, mastic or other durable sealing
method.
Filter Arrangement
FIRE, CARBON MONOXIDE AND POISONING
HAZARD
Failure to follow this warning could result in fire, personal
injury or death.
Never operate a furnace without a filter or filtration device
installed. Never operate a furnace with filter or filtration
device access doors removed.
!
WARNING
Table 6 – Air Filter Selection and Duct Sizing -- In. (mm)
FILTER
CABINET
HEIGHT
IN (MM)
FILTER SIZE --- IN (MM)
FILTER TYPE
14---3/16
{
(360)
14 x 25 x 3/4
(356 x 635 x 19)
Washable
or Media*
16 (406)
(1) 16 x 25 x 3/4*
(406 x 635 x 19) or
(1) 16 x 25 x 4---5/16
(406 x 635 x 110)
Washable
or Media*
21 (533)
(1) 20 x 25 x 3/4*
(508 x 635 x 19) or
(1) 20 x 25 x 4---5/16
(508 x 635 x 110)
Washable
or Media*
24 ½ (622)
(1) 24 x 25 x 3/4*or
(610 x 635 x 19) or
(1) 24 x 25 x 4---5/16
(610 x 635 x 110)
Washable
or Media*
* Filters with a side return---air may have a different filter size. Measure the
filter to obtain the correct size.
* Recommended to maintain air filter face velocity. See Specification for
part number.
{
Not all families have these models.
Filter and Return Duct Sizing
Pressure drop must be taken into account when sizing filters, filter
racks, IAQ devices, and associated system ductwork. See Table 7
for a comparison of Pressure Drop (initial/clean resistance to
airflow) versus Airflow for a variety of filter media types and sizes.
These are representative numbers. Consult the filter or IAQ device
manufacturers’ specification sheet for performance data for a
particular filter media or IAQ device.
Design the filter and associated ductwork for the best match of
pressure drop versus filter size. Best practice usually chooses filter
systems with pressure drops under 0.2 in. W.C. (50 Pa), with the
best blower electrical efficiency and system airflow performance
occurring with filter pressure drops under 0.1 in. W.C. (25 Pa).
Design the duct system FIRST to determine how much
pressure drop may be allowed in the filter system. See the Air
Ducts section. Excessive filter pressure drop often
compromises system airflow and duct performance, causes
inadequate airflow to the furthest ends of the duct system, as
well as causes excess noise and higher than anticipated
electrical consumption.
NOTICE
Provide duct transitions, as required, to smoothly transition airflow
from the return duct system to the filter (or IAQ device) to the
furnace when the dimensions of the ductwork or furnace return air
opening do not match the required filter or IAQ device dimensions.
See the instructions supplied with factory--accessory duct adapters.
Leveling Legs (If Desired)
In upflow position with side return inlet(s), leveling legs may be
used. See Fig. 26. Install field--supplied, 5/16 x 1--1/2 in. (8 x 38
mm) (max) corrosion--resistant machine bolts, washers and nuts.
NOTE
: Bottom closure must be used when leveling legs are used.
It may be necessary to remove and reinstall bottom closure panel to
install leveling legs. To remove bottom closure panel, see Fig. 24.
To install leveling legs:
1. Position furnace on its back. Locate and drill a hole in each
bottom corner of furnace.
2. For each leg, install nut on bolt and then install bolt with
nut in hole. (Install flat washer if desired.)
3. Install another nut on other side of furnace base. (Install flat
washer if desired.)
4. Adjust outside nut to provide desired height, and tighten in-
side nut to secure arrangement.
5. Reinstall bottom closure panel if removed.
1
3
/
4
1
3
/
4
1
3/4
1
3/4
5/16
5
/
16
5/16
5/16
(44mm)
(8mm)
(44mm)
(8mm)
(8mm)
(8mm)
(44mm)
(44mm)
A89014
Fig. 26 -- Leveling Legs
Location Relative to Cooling Equipment
The cooling coil must be installed parallel with, or on the
downstream side of the unit to avoid condensation in the heat
exchangers. When installed parallel with the furnace, dampers or
other flow control must prevent chilled air from entering the
furnace. If the dampers are manually operated, they must be
equipped with means to prevent operation of either unit unless the
damper is in the full--heat or full--cool position.
Platform Furnace Support
Construct working platform at location where all required furnace
clearances are met. See Table 1 and Fig. 27. For furnaces with
1--in. (25 mm) clearance requirement on side, set furnace on
non--combustible blocks, bricks or angle iron. For crawlspace
installations, if the furnace is not suspended from the floor joists,
the ground underneath furnace must be level and the furnace set on
blocks or bricks.
Suspended Furnace Support
The furnace must be supported under the entire length of the
furnace with threaded rod and angle iron. See Fig. 28. Secure
angle iron to bottom of furnace as shown.
Roll--Out Protection
Provide a minimum 12--in. x 22--in. (305 x 559 mm) piece of sheet
metal for flame roll--out protection in front of burner area for
furnaces closer than 12--in. (305 mm) above the combustible deck
or suspended furnaces closer than 12--in. (305 mm) to joists. The
sheet metal MUST extend underneath the furnace casing by 1--in.
(25 mm) with the door removed.
The bottom closure panel on furnaces of widths 17--1/2--in. (445
mm) and larger may be used for flame roll--out protection when
bottom of furnace is used for return air connection. See Fig. 27 for
proper orientation of roll--out shield.
