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Hot water plumbing

May 7, 2015
Catalina 22 Washington Sailing Marina
Retrofitting our 1982 S2 9.2A with a Kuuma 6 gal water heater that fits on the platform provided under the binnacle (water heater was an unexercised option). The boat was plumbed with what the owner's manual indicates is 5/16 I.D. plastic from the galley forward to the head lavatory, but the manual indicates hot water should run in 3/8 in copper tubing. Would I be crazy to try running hot water in the plastic tubing? Do you have any descriptions of the fittings that would finish the job, connecting the cold water back to the heater with its 1/2" female fittings, and hot water to the galley sink with its standard flex metal tubing, and on to the head (assuming copper needed in place of the existing plastic tubing)? Thanks for any experience, lessons learned, specifics.
Jan 4, 2006
Hunter 310 West Vancouver, B.C.
Also never heard of a boat with copper plumbing. Plastic tubing is so much easier and no metal taste if you plan to drink the water.

My '99 Hunter was factory installed with all plastic compression fittings (for which I cannot find the brand name to save my soul) and 1/2" plastic tubing.

I've done a lot of plumbing renovations and nothing could be easier and quicker.


Jun 3, 2012
Hunter 33 Steamboat Wharf, Hull, MA
5/16" and 3/8" seem too small to me. Hot and cold water are usually in 1/2" or 5/8" tubing. Plastic (reinforced PVC) will work fine. You may occasionally need to tighten a hose clamp.
May 7, 2015
Catalina 22 Washington Sailing Marina
Thanks, Gents! All good info. One thing that reassures me is the heater is limited to 140 degrees (electric-only) and I'm seeing most plastic hose specs good to 150 or 160. I'm going with the existing PVC--Worst case is a leak into the bilge.
Jul 7, 2004
Hunter 30T Cheney, KS
I replaced some PB (poly polybutylene ) on the front end of my water heater with PEX. PB works, but it is being phased out.
Feb 11, 2017
1983 S2 9.2A I have a retro hot water tank and line. The hose is plastic. Leave extra inches so can repair if needed. ie. leaking split ends.