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type L or type K copper pipe for water heating?

heatingFun Member Posts: 84
Which type of copper pipe are you using for hot water heating?


  • billtwocase
    billtwocase Member Posts: 2,385
    you mean type "M"

    for heating. Type "L" is for domestic. You can use either for heating, but there is a slight price difference
  • heatingFun
    heatingFun Member Posts: 84
    not type M

    Type M is the thinest pipe. I read from other place:

    As a general rule, use Type K whenever possible, Type L only when necessary, and Type M rarely.
  • Zman
    Zman Member Posts: 7,569

    I think the info you found is for underground water service. "K" is a thick walled soft copper that comes in a roll. "L" is thick walled and in my area is used for heavy commercial/industrial applications. I don't have experience in every part of the country, but I see "M" 99.9% of the time.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Ironman
    Ironman Member Posts: 7,376
    Use Type M...

    For hydronics; it's a closed loop system. As pointed out, type L is for well and potable (open loop).

    The only place I've seen type K is on government and industrial jobs; it's so thick that you have to use saws to cut it, tubing cutters are inadequate.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    Type "L" and "M" Copper Tube:

    The only time I have ever seen Type "L" used for heating is when it is specified to be used in the bid specifications. The only time I ever used Type L tube in heating was when it was specified in the plan/contract specifications. Or I ran out of Type M tube and needed a short piece to finish and I had a short piece in the truck. It was cheaper to use the short Type L than to go on safari to get a length of Type M.
  • MikeyB
    MikeyB Member Posts: 696

    Type M we always used for Hot Water Heating, used L tubing on HW systems when we had to buy the tubing underground, Type M offers les resistance to flow. Always used Tpye L for Domestic, actually saw a few times in Queens NY where M was used on a water heater and developed pin hole leaks. In our Commericial High Rise Buildings we require K Tubing for all Chill Water and All Hot Water Heating applications and all joints to be brazed
  • nugs
    nugs Member Posts: 77

    None of them are necessarily for heating or for domestic water and any of them will certainly be serviceable.  There was awhile when the plumbing code would not allow type m for domestic water but that rule has gone away. (at least it has here)  I have always used M for heating systems because it's less expensive and it's not subjected to high pressure or corrosive water conditions.  Type K has the advantage of being able to be bent which makes it handy for coming up through the sills of an old house but these days everyone is stringing HEPex because of the cost and it's a whole lot faster to install and you don't have to worry about burning the house down with your torch,
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