Replacement of a hot water iron pipe monoflow to pex or smaller copper

Discussion in 'HVAC Heating & Cooling' started by chuckdiy, Jan 15, 2010.

  1. chuckdiy

    chuckdiy New Member

    Messages:
    7
    Location:
    MA
    I have a 1 1/2" cast iron monoflow heating system with 8 convector radiators running off of the loop. I am looking to refinish my basement and would like to get some extra headroom. My house is 24'x44'. I'm inquring about the possibility of switching out the cast iron with pex or copper.

    I'm thinking I could possibly move the monoflow loop to one wall running the length of the basement (while switching it over to copper or pex). This way all of the headroom loss is in one area that is not often used.

    If I go the copper loop, I'd then have monoflow tees running 1/2" copper going to the convectors and running parallel to the joists and inside a ceiling. I guess my first question would be, can I replace my 2" cast iron pipe with 1" or 3/4" copper monoflow system? The second question would be, is there are concern with having the radiators up to 24' from the loop?

    If I go the pex route, I just saw that there are now pex monoflow tee by a company name Raven Products (link below). I'm now thinking I could maybe just replicate the current system with pex (but putting it up in the floor joists. Has anyone every used this type of product.

    http://www.ravenproducts.us/pex.htm

    I'm really looking for suggestions or any other ideas; things I should stay away from, etc.

    Also I have another general question. Is it OK to use Pex for a hot water heating system @ 180 degrees?

    Thanks in advance.
    Last edited: Jan 15, 2010
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    Most pex can withstand 180 degrees at low pressures. But, I don't think your system will work if you decrease the supply pipe diameter. The cross-section of a 2" pipe is 4x the size of a 1" pipe...you won't be able to pump enough heat around the system. If you used a manifold and ran home runs, maybe, but balancing things might get tougher. See what the pros think, but I think you'll have problems.
  3. chuckdiy

    chuckdiy New Member

    Messages:
    7
    Location:
    MA
    Thanks for the comments. I've just rechecked and I have 1 1/2" cast iron. Not sure if that makes the pressure situation better. Another thought is, could I swap out to a smaller pump to make the system pressure lower?
  4. chuckdiy

    chuckdiy New Member

    Messages:
    7
    Location:
    MA
    OK so I was thinking that maybe just dropping the monoflow system and going to a Two Pipe system would be much easier. The question would be is could I do this system with convector radiators and a 1" PEX pipe?
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    1.5" pipe is still 2.25x more volume than a 1" pipe. You need the volume to transfer the heat. You shouldn't use a bigger pump. In a closed system, the pump provides mostly the circulation of the water, and doesn't contribute to the system pressure. The pressure is dictated by the boiler used and the maximum height you need to pump the water. There's a limit on how big a pump you can use - move the water too fast (different than pressure), and it both becomes noisy and wears away the insides of the pipes.

    Hopefully someone better versed in this will comment over the weekend. My guess is you could convert this to a 2-pipe system, but the details would need to be assessed by someone who knows what they are doing (not me!).
  6. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    The smallest main you can run with monoflow tees would be 1 1/4. What you can't do is have a 24' horizontal run from the main to the convectors. As far as using pex I don't think you can get 1 1/4 x 1/2 monoflow tees in pex. As far as a two pipe system your main piping would have to start out at 1 1/2" then reduce as you pick up your convectors. At no point would it be smaller then 1".

    John
  7. chuckdiy

    chuckdiy New Member

    Messages:
    7
    Location:
    MA
    Thanks for your help, fellas. Much appreciated. Two more questions regarding the two pipe solution. Is there any downside to doing 1 1/2" Pex to a couple 4 output manifolds. Then having 1/2" Pex from each manifold output go to each convectors....and obviously reverse for the return water. And last question, is there any suggested or pex tubing or fittings to use (or NOT use)?
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