Should i use 1/2 " or 3/4" pex?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dp200, Feb 6, 2013.

  1. dp200

    dp200 New Member

    I have 3/4" water coming in to my hot water heater and then 1/2" to everything else.
    I live in a single wide trailer 70' x 14'.
    not sure if distance matters.
    I have seriously low pressure.
    takes 18 minutes to fill garden tub.
    I am remodeling plumbing due to water leaks in old grey pipes that are no longer legal and my insurance says I have to upgrade by may.
    I want to use pex.

    am considering using 3/4 inch throughout and then 1/2" to fixtures.
    does this end up increasing my pressure?
    does this increase my electric bill due to hot water sitting in lines?
    is it worth the extra money to increase size?
    do fittings inserted in pex decrease flow?

    I need help deciding.

    also need help deciding on connections.
    sharkbite, clamps, or whatever else is offered. crimps etc.
    which is lower cost?

    pipes will be under trailer exposed to cold but not in daylight.
    I am considering using the insulator sleeves to wrap pipes.

    any ideas, suggestions as to the proper way to do install under a trailer?

    thank you!!!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    Increasing the diameter of the pipe should supply greater volume, but it won't do anything to the pressure...don't confuse pressure with volume. I'd check the actual pressure you have - HD and any hardware store, sells a water pressure gauge. It's the only real way to know what you have now. Because it can freeze there, you want to make sure the pipe is run as close to the floor with insulation under it so that it traps some of the trailer's heat. Pex won't typically split if it freezes, but fittings can. Remember, insulation doesn't create heat, it just traps it. If there isn't any, the pipe will still freeze.

    3/4" pex is about the same ID as 1/2" copper, so yes, I'd run 3/4" pex to the bathroom group. The tub, I'd convert 3/4" to the likely 1/2" valve you have. Everywhere else, things are flow restricted, so 1/2" is plenty. Well, a washing machine might use the 3/4" up to it as well as a hose bib.

    Yes, larger pipe will hold more water, and let it take longer to get hot at the end (a recirc system might work out for you if things actually have to go that full 70'). But, as I said, 3/4" pex isn't much larger than 1/2" copper.
  3. dp200

    dp200 New Member

    thank you jim! any insight as to the best connectors to pex? I guess the number one consideration is the weather as you said typically fittings can split. are there better fittings than others?

    (and I will definitely install those wrapper insulation sleeves around pipes and I have extra strips of insulation I can probably wrap as well).

    messy job but I am certainly digging getting under the trailer and getting dirty.
    started out with leaking fixture that soaked much insulation.
    ripped out all insulation and now see MANY dripping fixtures.

    I guess fixtures are my real problem.
    any suggestions as to best fixtures are greatly appreciated.
    thank you sir!
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    New England
    It's hard to say what a trailer had, or whether 'standard' valves, etc. will fit easily. There are lots of discussions on pex, so a search and some reading time will help. Personally, I like Wirsbo/Uphonor, but their connection system requires a fairly expensive tool to make connections. I don't have enough experience with others to tell you what to stay away from.
  5. 6t7gto

    6t7gto DIY Junior Member

    Bedford, Ohio
    Quite a few pex crimpers on e-bay.

    buy it, use it, and put back up for sale.


    p.s. interesting that I couldn't put up the link for e-bay.

    Last edited by a moderator: Feb 7, 2013
  6. hj

    hj Moderator & Master Plumber Staff Member

    Cave Creek, Arizona
    Larger pipes will increase volume and should increase "dynamic" pressure. Insert fittings are an enigma. They do reduce the size of the line, but since it is for a very short distance, the water should compensate by moving faster at that point.
  7. LiveNLearn

    LiveNLearn New Member

    I just finished re-piping a significant part of the line from the street and into my house. Previously I had 3/4" galvanized and, based on the "good advice" from forums like this one, I used 1/2" PEX in place of the 3/4" galvanized. The flow rate is now less than 1/2 of what it was. Maybe it's the fittings that slow things down (the fit inside the PEX), but going with 1/2" was definitely a mistake. I should have used 3/4" PEX.
  8. Terry

    Terry Administrator Staff Member

    Bothell, Washington
    The only time 1/2" PEX may replace a 3/4" line is if you "home run" the system. Supply "each" fixture with it's "own" 1/2" supply.
    Sharing a 1/2" line with other fixtures can be sketchy.
    If you have an existing 3/4" line, and it's run in the same matter with branches, they it must remain 3/4" or even bumped to 1"
    PEX has the same outside diameter, and a lesser inside diameter. Add to that the restriction of the fittings which have an even smaller ID.

    I have run 1/2" PEX to the hot in a bathroom feeding one tub and one lav, and 3/4" cold PEX for the tub, toilet and lav.

    A tub valve needs a "full size" pipe to the tub spout if you are diverting to a shower head off of it. That would be copper or threaded galvanized or brass. PEX does not work in that location. It forces water to the shower head when the tub is filling.
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