I may have made a mistake. I just bought a tankless hot water heater with 1/2 inch water connection fittings. My house used 3/4 inch water pipes. Is it OK to reduce from 3/4 to 1/2 inch copper pipe and connect to the hot water heater and then as the water leaves the heater to go back from 1/2 to 3/4 inch copper pipe? Thanks for any info!

Hey Pisces:

No mistake there... not ideal.. but no mistake. There will be a drop in VOLUME.. but pressure should not decrease... read on.

Tankless coils at boilers are only 1/2" tappings...and most everyone connects 1/2" pipe to them or JUMP to 3/4" no problem.

Some tankless water heaters, like yours, actually want to have 1/2" tappings to control the volume of water getting heated at one time (3/4" tapping/feed may overwhelm the system and reduce ability to heat the water as fast as it does).

Still... I want you to call the manufacturer of your particular tankless water heater and I want you to pose this question to their technical department... just so you can be 100% sure. I don't want you to find out that this is in fact an issue later... say 1/2 way into winter next year (I don't even know what particular tankless hot water heater we are talking about.. so I am just GENERALIZING for you)!

Call them... let us know what they said... Mark

Connecting a fixture with 3/4" inlets with a 1/2" supply? Bad idea!
Connecting a fixture with 1/2" inlets off a 3/4" main with a 1/2" supply? Good plumbing practice! Another great answer by Mark. Tom