Thermo Pride Thermo Pace Downflow/Horizontal Furnace (CSA) - Manual (Page 17)

Installer’s Information Manual Page 17
For example: A 108,000 Btu per hour furnace requires two
openings of at least 108,000 ÷ 4,000 or 27 square inches.
See Figure 18 and Table 3.
Table 3. Free Opening Area Based On One Square Inch
Per 4000 Btu/hr.
TOTAL
INPUT
(Btu/hr)
REQUIRED
FREE
AREA PER
OPENING
(square inches)
MINIMUM
ROUND PIPE
DIAMETER
(inches)
MAXIMUM
INPUT FOR
GIVEN PIPE
DIAMETER
(Btu/hr)
54,000 13.5 5 78,000
72,000 18 5 78,000
90,000 22.5 6 113,000
108,000 27 6 113,000
126,000 31.5 7 153,000
144,000 36 7 153,000
When communicating with the outdoors through vertical
ducts, openings and ducts must have a minimum free area
of one square inch per 4,000 Btu per hour of total combined
input rating of all gas appliances within fu rnace space. See
Figure 19 and Table 3.
Figure 19. All Air Through Vertical Ducts From Spaces
That Freely Access The Outdoors.
Figure 20. All Air From The Outdoors Through Horizontal
Ducts.
When communicating with the outdoors through horizontal
ducts, openings and ducts must have a minimum free area
of one square inch per 2,000 Btu per hour of total combined
input rating of all gas appliances within fu rnace space. See
Figure 20 and Table 4.
Table 4. Free Opening Area Based On One Square Inch
Per 2000 Btu/hr.
TOTAL
INPUT
(Btu/hr)
REQUIRED
FREE
AREA PER
OPENING
(square inches)
MINIMUM
ROUND
PIPE
DIAMETER.
(inches)
MAXIMUM
INPUT FOR
GIVEN PIPE
DIAMETER
(Btu/hr)
54,000 27 6 56,000
72,000 36 7 76,000
90,000 45 8 100,000
108,000 54 9 127,000
126,000 63 9 127,000
144,000 72 10 157,000
Example: Furnace is 90,000 Btu per hour input and is to be
installed in a confined space that contains no other gas
appliances. Rectangular combustion and ventilation air
ducts will run horizontally from outdoors to fu rnace space.
Calculate the free area required.
Because combustion and ventilation air ducts run
horizontally, allow 2,000 Btu per hour.
Furnace input (Btu/hr) = Free area required
2,000 Btu/hr
per square inch
90,000 = 45 square inches
2,000
Each duct must have a minim um cross sectional area of 45
square inches.
SECTION 5. CONDENSATE DRAIN
This furnace produces water as a product of combustion.
Much of this water condenses on the stainless steel tubing
of the heat exchanger and in the vent system. This water
(referred to as condensate) must be drained from the
furnace into a household drain. The following notes should
be considered when connecting condensate drain:
??
The furnace’s drain trap must be primed. This is easily
done by pouring a few cups of water into fu rnace vent
pipe after drain installation is complete.
??
Field installed drain line from furnace must flow down
hill from furnace trap.
??
A frozen or blocked drain line will cause fu rnace
shutdown and “no-heat” complaints. Protect drain trap
and drain tubing from freezing.
??
When a condensate pump is used, select a pump
designed for fu rnace condensate.
CAUTION: Make sure that drain connections do not leak.
Air leaks around drain hoses will prevent furnace from
draining and cause the furnace to shutoff. Make sure all
hos e clamps are installed correctly.