I was looking up the clearances for the vent on a Paloma tankless water heater and found this on the installation guide:
“The vent can be installed with a slight downward slope of 1/4” per foot of horizontal run toward the vent terminal (see diagram below). This ensures that any condensate formed during operation of the unit is evacuated from the appliance”
Do the other tankless water heater manufacturers having similar installation recommendations? I would have never guessed that it was okay, or even recommended, to put a downward slope on the vent. I looked up a couple of different models (direct vent and non-direct vent) and the recommendations were the same.
The full PDF install guide can be found at: