I'm planning to purchase and install a new condensing tankless water heater (Takagi T-H3J-DV-N) that will supply both domestic hot water and space heating (radiant via heat exchanger, separate closed loop).
The gas connection on the water heater is 3/4", but my current line running to my existing water heater is 1/2", off of a gas manifold with a 1" service from the meter (manifold is on the other size of the wall from the meter, ~8" away).
The distance from the manifold to the new tankless heater is less than 8'. According to the natural gas sizing chart in the Takagi manual pg 26, a 1/2" line will carry over 172,000 BTU/hr over the 8' distance. The heater maxes out at 160,000 BTU.
I have two questions:
- Since the 1/2" pipe will carry the required amount of gas to operate the appliance, would increasing the line from 1/2" to 3/4" at the appliance cause any functional issues?
- In general, do plumbing codes prohibit increasing from 1/2" to 3/4", as long as the line is sized properly (for 1/2")?