4.6.3 Vent specifications
Establish vent clearances that comply with the vent
manufacturer's specifications and all applicable national/local
Minimum combustion air and exhaust pipe length
The minimum exhaust pipe length is 1 ft (0.3m) of straight vent
pipe. The minimum air intake pipe length is one 1 ft or one 90°
elbow or an air intake grill cap to prevent debris from falling into
Maximum combustion air and exhaust pipe length
The table 8 displays the maximum allowable straight pipe
lengths for air intake and exhaust piping. Reduce the maximum
allowable pipe length by the equivalent lengths for each elbow
used and termination used.
PROPER GAS PRESSURE!
The following section assumes the water heater will receive gas
pressure greater than or equal to 5" WC for the 199kBTU
models (4" WC for 160kBTU models). In cases of gas pressure
below 5" WC for the 199kBTU (4" WC for the 160kBTU models)
the maximum heat input is reduced.
The values of maximum flue length in table are 8 before any
deductions for elbows or terminations.
2" Twin pipe
3" Twin pipe
1) To assure maximum heat input at maximum vent length
minimum gas pressure should be 5" W.C. for the 199 kBTU
models and 4" W.C. for the 160 kBTU models.
Maximum Allowable Exhaust and Air intake Lengths
Greentherm T9900 SE/i – 6 720 813 635 (2019/03)
Improper gas pressure or vent length may result in undesired
symptoms or errors such as noisy burner, C1, C2, CF, EA, EC.
The vent for this appliance shall not terminate:
1. over public walkways; or
2. near soffit vents or crawl space vents or other areas where
condensate or vapor could create a nuisance or hazard or
cause papery damage; or
3. where condensate vapor could cause damage or could be
detrimental to the operation of regulators, relief valves, or