After a poor install, which the original contractor did not help out with, I contacted a Navien representative to assess problems with our on demand water heater. He suggested that our gas line looked to small and may be the problem.
I have 2lb gas pressure coming into my house. The contractor has installed some 1/2" and some 3/4" iron pipe. The sizing goes as follows: about 4" of 1/2" pipe coming out of the meter. This is joined to about 45' of 3/4" pipe. Then it is reduced down to about 5' of 1/2" pipe connected to a regulator which feeds into a 60,000 BTU furnace. After the furnace about 8' of 3/4' pipe goes to a 170000 BTU on demand water heater. Our incoming 2lb of pressure is classified as "high pressure" by Terasen, out local gas provider. Is the mixture of 1/2" and 3/4" pipe put in by the installer sufficient? Since I may have to redo the piping, I was wondering what is the max CFH @2psig from a 3/4 in 45' pipe?
Thanks
Joe

Hello Joe, unfortunately, your gas line is grossly undersized. You have 230 000 Btu's connected by 1/2" pipe. It just won't work...

That gas line should be at least..... without looking at the tables .... about 1 to 1 1/4" for 45' developed length.