My house copper lines are 3/4 in and my new water heater accepts 1/2 copper in a compression connection. Is there any issue with adding a 3/4 to 1/2 reducer before and after the heater?

  • 2
    no there is not
    – jsotola
    Commented Mar 9, 2018 at 5:31
  • What type of water heater is this? I thought only point-of-use (POI) units were 1/2" or even 3/8", but pretty much any whole-house water heater would be 3/4"...
    – Hari
    Commented Mar 9, 2018 at 6:06
  • ECO 11 cdn.globalimageserver.com/… "1/2 CF connection"
    – Alex
    Commented Mar 9, 2018 at 6:07

1 Answer 1


Just doing the math for the area A = πr2

  • 1/2 inch pipe that is A = π(.25)^2
  • 3/4 inch pipe that is A = π(.375)^2

You can see the difference in area and that changes the amount of volume that will flow. Your water heater has a flow rate based on its piping and therefore it will be the limiting factor. Your house could handle more.

The only problem I can foresee possibly happening and would be most likely after install is that your 3/4 pipes could have an air gap but this should dissipate over time by running the water slowly in order to fill the line and build pressure.

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