According to ANSI code, gas tankless water heaters normally require stainless steel, category II/III vent pipe. This is due to the fact that gas tankless water heaters actually burn at a higher BTU rating. As such, the gas is extremely hot when it leaves the water heater, but cools quickly. This cooling process results in acidic condensation which could eat through regular galvanized pipe.
Eccotemp Systems recommend using Z-Flex vent pipe. Both of the i12 and FVI12 models use 2.5" single walled venting while the 45 Series uses 4" single walled venting.
Installation requirements: Horizontal Termination
We always recommend a horizontal installation when it is possible. It requires less pipe and as such, less expensive. When doing a horizontal run, your maximum lengths are as follows:
1 elbow: 47' 6"
2 elbows: 42' 6"
3 elbows: 37' 6"
Each elbow is equivalent to 5' of straight pipe.
Installation requirements: Vertical Termination
When installing a vertical vent stack, you will need the following pieces:
Universal appliance adapter
Drainpipe for condensation
NOTE: A TERMINATION HOOD OR STRAIGHT PIPE SECTION MUST BE EQUIPPED WITH A DAMPER/BACKFLOW PREVENTER IS MANDATORY TO ENSURE THAT FREEZING AIR DOES NOT COME BACK DOWN THROUGH THE VENT STACK. THIS MAY CAUSE FREEZE DAMAGE INTERNALLY IN THE WATER HEATER AND IS NOT COVERED UNDER WARRANTY.