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is the flow rate of 3/4" pex enough

rich67 Member Posts: 21
for my hot water baseboard heating? I reinsulated the walls in one room of my 960 sqft ranch and am replacing the baseboard units. I ripped out all the old 3/4 copper and want to run pex to the new units and reconnect to existing system.

I am noticing that 3/4 pex looks like 3/4 ID while copper is 3/4 OD. Is this true?

The main zone runs the perimiter of the house about 130 ft loop all 3/4 copper except what I want to replace. The circulator is Taco 007. Am I choking off the water supply by using pex?

I'm sure I omitted some tidbits of info that you would need. But any help is appreciated.



  • SpeyFitter
    SpeyFitter Member Posts: 422
    Based on info, should be fine...

    If memory serves me correctly, for the 2 to 4 feet per second recommended flow rate for Copper is from about 3.2 GPM to 6.5 GPM. At 20 degree delta T that is 32,000 BTUH to 65,000 BTUH's worth of heat loss. If you go with larger Delta T's, then you're looking at lower flow rates (more heat transfer time) to widen that delta t.  

    It's a 934 sq. foot rancher? Even with slight differences in friction, and the fact the fittings aren't as large as the pipe (compared to Copper where the fittings are as large as the pipe), 3/4" pex should be ok. Just do your best to try and minimize the fittings - try and use those black open bend supports instead, if possible (they are a b*tch to get on 3/4" sometimes but they do make a difference in pressure drop), when you need a serious change in direction. Even with poor insulation and old single pane windows and a cold environment I don't see a 934 sq. foot ranger seeing more than 30,000 BTUH' heat loss on a 0 degree F design day. My 1000 sq. foot rancher in Vancouver with 19 degrees F design temp (newer double pane windows, R12 insulation, etc.) has a 17,000-ish heat loss.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • rich67
    rich67 Member Posts: 21
    Yes, the pex 90 fittings are tiny inside

    I went to 3 supply houses on Saturday. 2 places had little to no pex fittings. They wanted to know how come I just didn't rerun in copper. I suppose for my purpose I could have but, I just had to try it out. My plan is that as I redo each room, (kitchen, baths, etc.) I'll pipe with pex. I just need to find a supply house that has the parts I want. Thanks for the advice I'll stay away from fittings as much as possible.
  • Ironman
    Ironman Member Posts: 6,555
    Make Sure...

    That you use O2 barrier pex or you'll ruin your boiler.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • rich67
    rich67 Member Posts: 21
    Yes, I'm using barrier tubing

    thanks for the heads up. Hopefully I'll start installing this weekend.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,195
    I am curious why you are replacing

    the copper with pex. I could see if you were going from new but the copper is already there.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • rich67
    rich67 Member Posts: 21
    I had some construction work done.

    So I had to take out the pipe to make room. Some of the fittings were corroded anyway. So I thought I'd try pex when reinstalling.
  • Magnehelic
    Magnehelic Member Posts: 63
    Shark Bite

    fittings can be bought at most ACE hardware stores........I think they'll do pretty much any material joining.......but you need to make sure before using them.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,195
    Please use the fittings

    That are specified by the manufacturer of the piping and use the joining method they recommend. This way is anything does go wrong with recalls or any such nonsense it is one singer one song. I would have stayed with copper if it were my job or my house. But your reasons do hold water. Yes that was a terrible pun.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
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