I am about to install a tankless heater and have a question for the "Pros" in here as to what they would do in this instance.
It is a single family home, one bath, kitchen, D/W, etc.
The water heater (Rinnai) has the 3/4" supply and cold water inlet. However, the water service to the house is only 1/2". That being said, which of the following would you do:
-Call the municipality and try and get the service upsized?
-Run 1/2 make up water to the heater, then use a 3/4" x 1/2" red at the connection?
-Tee off the water main and increase size to 3/4" and run it to the heater.
It is worth noting that the house did have a back apartment, and that had it's own separate water heater, but again served by the same 1/2" service listed above. The apartment is not used now, nor will it be in the future.
Not sure what 3/4" main you are going to tee off from. Any connections should be made after the meter. I have seen this problem being asked about before, and it troubles me that some have said to just put a 1/2x3/4 adapter at the unit. The heater must need the volume of a 3/4" line to operate properly. If there was a warranty issue, this would violate the installation process. I would contact Rinnai and inquire about this since their units are not cheap.
If you have never made a mistake, you haven't done much.