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12. DUCTS AND REGISTER MEASUREMENTS
(sample calculations)
SIMPLIFIED METHOD
DISTRIBUTION SYSTEM
Ducts size (heat)
4 inch outlet reduce by 1”
5 inch outlet reduce by 2” Always by 8” thick
6 inch outlet reduce by 3”
N.B.: The main duct must be reduced every 2
outlets.
Ducts specifications (heat)
Dimensions Length Elbow Average equivalence
4”
10’
1 x 90
o
Max 4,000 Btu
5”
10’
1 x 90
o
Max 6,000 Btu
6”
10’
1 x 90
o
Max 7,000 Btu
DAMPER
For a 4” warm air outlet: 2” x 10” damper
For a 5” warm air outlet: 2” x 12” damper or 4” x 10”
For a 6” warm air outlet: 2” x 14” damper or 4” x 12”
WARM AIR SYSTEM INSTALLATION
HOUSE DIMENSIONS
Example: 28 x 40 bungalow: 1,120 sq. ft.
28 x 40 x 8: 8,960 cu. ft. x 1.8 Ch. air/hr:
16,128 Btu
Exposed walls:
40 + 40 + 28 + 28: 136 x 8: 1,088 cu. ft. x 22: 23,936 Btu
Number of windows:
12 of 3 x 4: 144 x 60:
8,640 Btu
Number of doors:
2 x 3 x 7: 42 x 100:
4,200 Btu
52,904 Btu
Non-insulated basement:
25%
Insulated basement:
15%
7,906 Btu
or 54 Btu per sq. ft.
60,840 Btu
FOR ELECTRIC ELEMENTS 80%:48,672 Btu or 14,28 kW
TO BE ADDED: House 1 1/2 floor = 25%
House 2 floors = 40%
BEDROOM (for example: 12 x 12)
12 x 12 x 8: 1,152 cu. ft. x 1.8 Ch. air/hr:
2,074 Btu
Exposed walls:
12 + 12 x 8: 192 x 22:
4,224 Btu
Windows:
3 x 4 x 60
720 Btu
7,018 Btu
