M or L copper?

TomTA

I'm replacing pretty much everything in my boiler/DHW/radiator systems. Keeping a couple of the decorative cast iron radiators, but virtually everything else needs to be replaced. Existing piping to radiators is iron; some left over from gravity-feed days, some more modern 1.25" OD iron. I'm inclined to just start from scratch and re-pipe the radiator system with copper. Is type M OK, or should I stick with L? I can find GPM flow data and head loss data for pex and copper, but nothing for iron. Would 1" or 1.25" copper on the radiator runs cause excessive head loss compared to the existing iron? I'd like to go with 1" obviously, but since this is a one-time expenditure (knock on wood) the additional cost of 1.25" can be dealt with.

Larry Weingarten

Hi, It seems an ideal time to do heat loss calculation using an online calculator like Slant/Fin. This will get you the gpm flows needed and from there you can size the pipe. What temperatures are you looking at? Maybe PEX could work? DHW should be sized separately and for expected flow, based on the pressure available. Water quality plays into this also. Type M is basically OK for low intermittent flow and good water.

I seem to have expanded your question, but there seems to be more to take into account to get good life and service.

Yours, Larry

JohnNY

We've been using M copper on heat for decades with no issue but some higher end projects specifically call for L tubing.

TomTA

Larry Weingarten said:

Hi, It seems an ideal time to do heat loss calculation using an online calculator like Slant/Fin. This will get you the gpm flows needed and from there you can size the pipe. What temperatures are you looking at? Maybe PEX could work? DHW should be sized separately and for expected flow, based on the pressure available. Water quality plays into this also. Type M is basically OK for low intermittent flow and good water.



I seem to have expanded your question, but there seems to be more to take into account to get good life and service.



Yours, Larry

Thanks, Larry. According to the Slant/Fin calculator I need about 70k. That's with stingy indoor temps, and I wasn't sure how to incorporate the stairwell, so 80k might be more in line. The indirect comes with 1" supply/return connections, so I just assumed I'd run 1" from the boiler circuit to the indirect. We're on insanely hard well-water, and I'm not sure if hard water or softened water is worse for the insides of the closed system.

I was reading on some other posts for steam systems that you don't use copper for the near-boiler piping due to temperature expansion/contraction for copper versus iron. Does the same thing apply for a hot-water system running at 180? Most of our near-boiler piping was replaced with copper last time around (well before we bought the place), but the runs to the radiators are still iron.

mattmia2

Copper is fine for hot water. Need to arrange it or any other piping system so it can move as it expands and contracts with temp changes.

Use the calculator to find the loss per room, that will let you calculate what supply you need to each room. I would be inclined to use pex for most of it both from a cost and ease of installation standpoint. .5" and .75" pex which is probably adequate for the feed to each room is easy to route. Larger pex is much stiffer and harder to work with and you may be better off fitting copper or at least fitting elbows in to the pex for the larger runs like to the indirect and main piping if you have that sort of arrangement rather than home running each room.

BobC

Copper is not good for steam piping because the expansion and contraction can cause joints to fail. It's ok for hot water because the amount of expansion is usually less. Copper also does not take kindly to being firmly fixed at both ends while it's expanding and contracting.

If you repipe the radiators be sure to mind the slope of the pipes and be sure to use swing joints so things can mve to accomodate expansion of the piping.

Bob

EBEBRATT-Ed

Copper M tubing is fine for heating. Hot & cold domestic water needs to be type L.

I agree with @Larry Weingarten size the new piping base on what flow it needs

HVACNUT

> @JohnNY said:
> We've been using M copper on heat for decades with no issue but some higher end projects specifically call for L tubing.

Some towns and villages require L copper for heating as well. On Long Island anyway.

Intplm.

Have been using type -M- copper for many, many years now for domestic hot water heating systems. It has been the preferred type of copper used for this purpose that you are describing.