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Repiping hot water system with pex

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Nick_27
Nick_27 Member Posts: 16
in THE MAIN WALL
Hi TimCo:

The lengths of each of the runs is 5', 7', 7', 7.5 ', 8', 8.5', ~8.6', 10', 14'. The emitters are all cast iron rads and there are 9 of them. The boiler is in the basement and all rads but a basement one is on the 1st floor. They currently have regular valves but I'd like to replace them with thermostatic valves. The approx system volume is about 40 gallons (currently with the big iron pipes). The boiler max is 180 degrees. The each radiator is fed by branches from the main line with a pump in place - homerun system (it's not a loop system, it's a gravity system converted to gas with a circ pump).

Thanks for your help TimCo!!! This forum is great.

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  • Nick_27
    Nick_27 Member Posts: 16
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    Pex to replace iron pipes in hot water radiator system

    Hi All: I want to remove these big iron pipes from my hot water heating system. It was previously updated with a circulator pump and gas boiler (from the 70's), and copper 1" pipes coming off the boiler system, but they left all the huge 3" riser pipes in place in the basement which really get in the way. I was thinking of just cutting them off and repiping the whole system with pex (pex-al-pex, i.e. with an oxygen barrier). It would then be possible to hide all the pipes and actually use the basement. Is there any problem with this idea? And what diameter of PEX should I use? 1",3/4"?
  • Timco
    Timco Member Posts: 3,040
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    We would need to know the length of runs, # of rads, or type of emitters for each zone. Circ type?

    Tim
    Just a guy running some pipes.
  • Nick_27
    Nick_27 Member Posts: 16
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    Data for TimCo

    Hi TimCo:

    The lengths of each of the runs is 5', 7', 7', 7.5 ', 8', 8.5', ~8.6', 10', 14'. The emitters are all cast iron rads and there are 9 of them. They currently have regular valves but I'd like to replace them with thermostatic valves. The approx system volume is about 40 gallons (currently with the big iron pipes). The boiler max is 180 degrees. The each radiator is fed by branches from the main line with a pump in place (it's not a loop system, it's a gravity system converted to gas with a circ pump).

    Thanks for your help TimCo!!! This forum is great.
  • Nick_27
    Nick_27 Member Posts: 16
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    Would it really change things that much?

    It seems the only side effect of getting rid of the big iron riser pipes would a decrease in the volume of the system somewhat. I wouldn't be changing anything else in the system. (At least until I can afford to replace the boiler with one of those hi effic ones.)
  • Nick_27
    Nick_27 Member Posts: 16
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    Will pex radiate more heat than iron?

    Will replacing the iron pipes with pex mean they'll radiate more heat in the joists? I wouldn't think so...
  • Dennis
    Dennis Member Posts: 101
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    Do it it will work fine,

    I do this in every rental property I own, along with installing a boiler to service each apartment.
    You have the right idea, Pex Al Pex is the way to go. Replace every valve with a TRV, also install valves on the manifold connections to adjust flow to the radiators.

    As far as the pex diameter, you will need to calculate the the heat loss of each room, or of each radiator. Most Joe Lunch Box homes have radiators that emit much less than 15,000 btu's so 1/2 pex will work for each radiator.

    Just do it, right.
  • Timco
    Timco Member Posts: 3,040
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    This is how I piped my 4-plex. While all the rads are drained, this is your chance to zone, zone, zone. I used 3/4" hpex and a 2-pipe system on the longest runs (25' each direction on the longest) and a simple series loop on the shorter 7-10' runs tot he small units such as the studio with two rads. Works great. Pex will lose less heat, and has no real drawbacks when removing large old gravity pipes. A 15-58 FC Grundfos will do very well for each zone, and a Taco 4-zone controller for the brain. I use all copper until the pipe hits the ceiling, then all pex except for penetrating the floors, which brass nipples on brass valves looks best. I do not use TRV's when zoning to your desired zones. Just when you have a loop that you want certain rads to be cooler on.

    Tim
    Just a guy running some pipes.
  • Nick_27
    Nick_27 Member Posts: 16
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    Floors and pipes

    Thanks for the encouragement! I appreciate it.

    By the way, like you said Tim, when the pipe comes up through the floor, I don't think 1/2"pex would look that good. You mention using a brass nipple, but what about just an iron pipe nipple (PEX for the run but then pipe through the floor)? (It's gonna be painted white anyway because...why?....well don't ask me I'm not the decorator.)
  • Timco
    Timco Member Posts: 3,040
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    blk iron is fine, but why 1/2"? That will greatly reduce your flow. Pex is already much smaller than copper at the fittings, and with 1/2" up to the rads, that's pretty tight. I would use 3/4" in & out of the rads...the brass is just for looks and can be undone easily later.

    Tim
    Just a guy running some pipes.
  • Nick_27
    Nick_27 Member Posts: 16
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    1/2\" versus 3/4\"

    I see your point Tim. I actually have some 1"pex-al-pex that my brother gave to me (construction worker) but that's a little big don't you think? I'll probably go with the 3/4" as you suggested.

    Thanks!
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