Filter
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All installations and services must be performed by qualified service personnel.
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K. FILTERS
1. CHB1 MODELS: HIGHBOYS
It is necessary to cut the return air opening in the bottom or side casing depending upon the needs of the specific
installation.
NOTICE: If your CHB1 will require air delivery above 1800 CFM, it is advisable that both sides, a combination of
1 side and the bottom, or the bottom only be used for return air. (If a return is cut in the bottom, it should be as large
as the return opening in the equivalent CDB1 model. (See specification sheet in beginning of this manual).
This CHB1 furnace has been factory supplied with a high quality re-usable filter rated for air velocities up to 600
ft/min. An optional Thermo Products filter rack assembly (part no. AOPS7547 for CHB1-50 thru 100 and
AOPS7375 for CHB1-125) is available which is sized for the filter provided.
If an optional Thermo Pride filter rack AOPS7547 (figure 19) is used with the furnace, it will serve as a template to
scribe a mark for the return air opening on the casing. Place the filter rack on the casing one inch up from the bottom
of the furnace and centered from side to side. Place the securing flange against the casing for locating the return air
opening.
Figure 19
PLEASE NOTE: While scribing the return air opening, the filter rack can be held into position by tape or similar
means.
Position the open end of the filter rack so that it is accessible for filter replacement. Once the filter rack is positioned
correctly, scribe a line along the inside of the securing flange of the filter rack on three of the sides. To scribe a line
on the fourth side, on the open end, use the open end support for a guide.
Remove the filter rack and cut the return air opening in the casing. Now the filter rack can be permanently attached
to the furnace with screws or pop-rivets along the securing flange.
Connect the return plenum to the filter rack and slide the filter into place.
2. CDB1 MODELS: COUNTERFLOWS
This CDB1 furnace has been factory supplied with two high quality reusable filters rated at 600 ft/min. These filters
are designed to be mounted on the return air plenum opening on the top of the furnace in the double “vee” style rack
provided (see Figure 20). If feasible, it is recommended that slits be cut in the return front to allow for easier access
of the filters.