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All installations and services must be performed by qualified service personnel.
10
intake systems must be considered. This includes all elbows, or equivalent pipefittings, used inside the
furnace jacket in addition to those used to construct the termination. Furthermore, a credit of 5-feet of
straight pipe may be taken for each elbow, up to maximum of three (3) elbows, which is dropped from the
maximum permissible number for each system.
Table 2: Maximum Permissible Exhaust Vent and Combustion Air Intake Lengths When Using the Maximum
Quantity of Elbows
Thermoplastic
Pipe Vent Size
(Nominal)
2 in. Diameter IPS
3 in. Diameter IPS
Furnace Model
Exhaust or
Intake
Straight
Pipe
Length (ft.)
Maximum
Qty. of
Exhaust
Elbows
1,2
Maximu
m
Qty. of
Intake
Elbows
2
Exhaust or
Intake
Straight
Pipe
Length (ft.)
Maximum
Qty. of
Exhaust
Elbows
1, 2
Maximu
m
Qty. of
Intake
Elbows
2
CHB1 / CDB1-50
35
8
7
-
-
-
CHB1 / CDB1-75
CHB1 / CDB1-100
Not Permitted
35
8
7
CHB1 / CDB1-125
Superscripts:
1
The drain tee supplied with CHB1 / CDB1 furnace model series is considered equivalent to one (1),
90° elbow.
2
Two (2), 45° elbows can be substituted for one (1), 90° elbow.
Care should be taken to design the shortest possible intake and exhaust systems. Each system should contain
as few elbows as possible to insure the satisfactory operation of the furnace. However, system length
should never be less than 8 ft of pipe with two (2), 90 deg. elbows. For best overall operation of the
combustion system, we recommend the actual equivalent lengths for both the constructed intake and the
exhaust systems have approximately the same value.
9. Use a saw designed to cut thermoplastic pipe. All cuts should be made at right angles to the pipe wall.
Smooth jagged edges and remove all burrs and strings. All pipe joints must utilize standard PVC
Schedule 40 series, DWV type elbows, couplings, and fittings. Clean all pipe surfaces at connections
using a fine abrasive material or approved PVC cleaner (primer). Secure all pipe joints using suitable
permanent PVC pipe solvent cement. Joints are NOT to be made by simply gluing raw edges of butted
together vent pipe.
Piping joints inside the furnace vestibule should be sealed with silicone caulk, rather than pipe cement, to
allow for disassembly and removal of piping, if necessary, during maintenance.
NOTICE: DO NOT use silicone caulk to seal the pipe sleeve or coupling to the metal air intake collar
on the burner box. Securing the sleeve or coupling to the collar using a screw is sufficient.
10. Vent connections shall be checked for leakage with the furnace induced draft blower running and with the
vent termination blocked. Use a mild soap and water solution to check for leaks.
11. Vent pipe passing through an unheated space shall be insulated with 1-inch thick, foil-faced fiberglass
insulation, or equivalent, to prevent freezing of condensate within the pipe.
12. No clearance is required from the outer surface of the thermoplastic piping to combustible materials for fire
hazard prevention.
13. Thermo Products does not require screens be installed in the exhaust vent and air intake piping. However,
optional stainless steel screens are available from Thermo Products, should the homeowner request them.