Combustion & Ventilation Air (cont.)
If horizontal ducts are used, the free area of each open-
ing must be at least 1 square inch per 2000 Btuh com-
bined input of appliances in area.
GRILLES CONNECTING ROOMS TO MAKE
UNCONFINED SPACE
FOR EXAMPLE: Your furnace is rated at 80,000 Btu per
hour. The water heater is rated at 30,000 Btu per hour. The
total is 80,000 Btu per hour. You need two grilles, each with
20 square inches of free opening, unless connected by
horizontal ducts which would require each grille or open-
ing to have a free area of 40 square inches.
*Openings for inlet or outlet air should not be made into
attic area if attic is equipped with a thermostat controlled
power vent.
FREE AREA IN SQ.INCHES - EACHOPENING (FURNACE
ONLY) - BASED ON ONE SQ. INCH PER 4000 8TUH
Furnace
Btuh / Input
30,000
35,000
40,000
45,000
50,000
60,O00
Req'd Number of Holes
Sq, Inch Sill or Header Plates
of Opening 1_/2'' 2" 3"
7.5 7 4 2
8.75 8 5 2
10.0 9 5 3
11.25 10 6 3
12.5 11 6 3
15.0 13 8 4
Recessed Mount Installation
FIND THE STUDS (See CAUTION on page 6)
CUT WALL OPENING
Use a stud Iocator or small finishing nails. Repeatedly
drive and remove a nail into the wall in the area of the
stud until it is located. Then find the inside edge of the
stud. Leave the nail at this location.
The other stud should be about 14-1/2 inches from the
one found. Drive finishing nails on the insides of this stud.
Draw wall cut out to required size as shown in Fig. 13,
page 12. If wall studs are not on 16 inch centers see
"CLOSE OFF STUD SPACE," Fig. 12, page 12.
Provide an opening as shown in Fig. 10, page 11. Work
from the top in the attic to cut away the ceiling plate.
ATTACH HEADER PLATE
MODELS: 5508331; 5508332; 6508731; 6508732
Locate header plate (Fig. 10, page 11) between wall studs
at 88V2 inches from finished floor and nail into position
with end flanges pointing up.
--10--
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