035-15241-003 Rev. A (201)
10
Unitary Products Group
DOWNFLOW (50-125 MBH MODELS ONLY)
Filters must be mounted in a location where they are easily
accessible for replacement, either behind a central return air
grille or in a filter box mounted on top of the furnace as shown
in Figure 7. A filter rack is supplied with the furnace. The table
lists the minimum filter sizes.
UPFLOW
An appropriately sized permanent cleanable or disposable fil-
ter shall be used. The filter should be installed in a side return
filter rack or, if bottom return is to be used, in a suitable filter
box under the furnace. Filters must be located external to the
furnace casing. See Figure 8.
HORIZONTAL
An appropriately sized permanent cleanable or disposable fil-
ter shall be used. The filter should be installed behind a return
grille or other location with easy access for filter change.
Locating the filter in a crawl space, attic or other inaccessible
location will result in filters not being changed as frequently
as recommended.
GAS PIPING
Before installing gas piping, check with local code authorities
for requirements concerning gas piping.
In the absence of local codes, follow the recommendations
contained in NATIONAL FUEL GAS CODE ANSI Z223.1 for
gas piping materials, pipe sizing, and the requirements for
installation. In Canada, refer to the latest edition of the CAN/
CGA-B149 Installation Code and local codes for specifics. It
is recommended that a gas cock shutoff valve be installed in
the gas supply line outside the casing, where it is readily
accessible, as close to the furnace as is practicable, as
shown in Figures 9, 10 and 11.
An 1/8 in. NPT (plugged) pressure tap for test gauge connec-
tion must be installed in the gas supply line immediately
upstream from the furnace, if local authorities do not allow
use of the pressure tap in the gas valve for this purpose.
Install a dirt leg at the bottom of any vertical riser or drop, as
close to the furnace as possible, to collect moisture and for-
eign material. Install a ground joint union just ahead of the gas
control valve. A typical downflow arrangement is shown in Fig-
ure 9. A typical upflow arrangement is shown in Figures 10, 11.
When making the connection at the gas control valve, use a
wrench on the inlet side of the valve to prevent any possible
twisting of the valve body, which could cause damage and
leaks. When making up pipe joints, use pipe thread com-
pound which is resistant to natural and LP (propane) gases.
FIGURE 7: DOWNFLOW FILTERS
(50-125 MBH MODELS ONLY)
INPUT
BTUH
Furnace
Width
Cleanable
Filter
Disposable
Filter
50,000
17-1/2
14 x 20
(2) 10 x 20
75,000
17-1/2
14 x 20
(2) 14 x 20
75,000
21
16 x 20
(2) 16 x 20
100,000
21
16 x 20
(2) 16 x 20
100,000
24-1/2
20 x 20
(2) 20 x 20
125,000
24-1/2
20 x 20
(2) 20 x 20
ACCESS
PANEL
FILTERS
FILTER
RACK
FIGURE 8: UPFLOW FILTERS
Use only the type of gas for which the furnace is
equipped. Using the wrong gas could create a
hazard, resulting in damage, personal injury or
death.
SIDE
RETURN FILTER
BOTTOM
RETURN FILTER