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Boiler repipe with pex

saxsquad29
saxsquad29 Member Posts: 8
Hi
I have a Weil McLain VHE series boiler 72000 BTU and cast iron radiators. I am planning on using a pex manifold with flow meters and balance valves. 1/2" pex to each radiator.
My questions are:
I purchased a rifeng SS manifold already, but it's only good up to max 158deg. Will this work with my cast radiators and current boiler?
Also, with this setup, do I really need these big b&g flow control valves near the boiler with the manifold?

Pictured is my current setup.
Thanks
Brian

Comments

  • EzzyT
    EzzyT Member Posts: 1,167
    So your doing a home run set up for the radiators into a manifold station, you won’t need those flow control valves nor any of that old big piping. 
    Did you do a room to room Heatloss analysis on the house along with a heat emitter survey to determine what is the lowest operating temperature you can run at based on the coldest days of the year in relation to the heat loss analysis?
    If you can operate at low to medium temperatures a new high efficient boiler might be something you want to look at to. What are you doing about zoning  or are you operating with trvs on the radiators? Either way you might need a buffer tank to prevent the current or a new boiler from short cycling .
  • saxsquad29
    saxsquad29 Member Posts: 8
    Yes, performed heat loss and calculated what each radiator could put out. Given that, the lowest temp would be about 150-160 deg F. I plan on using trvs at each radiator.
    If the boiler was properly sized, what would cause short cycling?
  • Jamie Hall
    Jamie Hall Member Posts: 16,651
    Problem. You have calculated that the lowest temperature you can run will be around 150 to 160. And the Rifeng manifold has a maximum temperature of 158.

    Um... really? Does not compute...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • saxsquad29
    saxsquad29 Member Posts: 8
    Yeah, I will have to find another manifold that can handle the higher temp. I got the manifold thinking it's max was 180-200 just like most I was looking at. After I purchased it I did more digging and realized its max was only 158.
  • Jamie Hall
    Jamie Hall Member Posts: 16,651
    Done that. It happens...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • JakeCK
    JakeCK Member Posts: 258
    Could you tighten the envelope so you would have lower water temps?
  • EzzyT
    EzzyT Member Posts: 1,167
    @geno907 a hydro separator won’t prevent boiler from short cycling. 
    mattmia2Ironmangeno907
  • saxsquad29
    saxsquad29 Member Posts: 8
    With my new setup- 1/2" pex manifold to each radiator with pex-al-pex, 1 1/4" boiler piping to manifold. TRV on each rad, 88000 BTU WM VHE-4 boiler. It doesn't short cycle now with the larger galvanized pipe, so why would it short cycle with switching to 1/2" pex?
  • Ironman
    Ironman Member Posts: 6,478

    With my new setup- 1/2" pex manifold to each radiator with pex-al-pex, 1 1/4" boiler piping to manifold. TRV on each rad, 88000 BTU WM VHE-4 boiler. It doesn't short cycle now with the larger galvanized pipe, so why would it short cycle with switching to 1/2" pex?

    You just stated the reason it doesn't short cycle now: large pipes. Actually, they're probably black iron. The large pipes and their water content add a lot of mass (buffer) to the system. You're planning on removing that.

    If the boiler is oversized, you're subject to short cycling. Adding TRVs is good idea, but that can also increase the likelihood of short cycling since many of them can be partially or fully closed at any given time. The mass of the cast iron rads is in your favor, but that may not be sufficient depending upon the other factors.

    If you find any old orifice plates in the inlet of any of the rads, they should be removed when using TRVs.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Ironman
    Ironman Member Posts: 6,478
    Make sure you use O2 barrier pex, not standard plumbing pex.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Leonc
    Leonc Member Posts: 16
    I'm planning the same thing, and made the same exact mistake with the manifold. I returned the one I got initially, and ended up with the caleffi, which had a rating up to 180 degrees. Bonus with the caleffi, that it is approved to be used upside down, so I can avoid looping the pex-al-pex downward into the bottom of the manifolds.
  • saxsquad29
    saxsquad29 Member Posts: 8
    Question on the pex al pex return and supply lines- can they all be touching and ziptied together. I've ran the boiler and the supply lines getting fairly hot when the water temp is at 140 degrees. Just wondering if the hot supply and cooler return lines touching would impact the efficiency of system.
  • saxsquad29
    saxsquad29 Member Posts: 8
    Just reposting this question about my boiler and pex manifold set up. Question on the pex al pex return and supply lines- can they all be touching and ziptied together. I've ran the boiler and the supply lines getting fairly hot when the water temp is at 140-170 degrees. Just wondering if the hot supply and cooler return lines touching would impact the efficiency of system
  • Jamie Hall
    Jamie Hall Member Posts: 16,651
    You will get a small loss of efficiency as the hot water going in will transfer heat to the cooler return. How much loss will depend on how much length is tied together and the temperature differential. A few percent, perhaps.

    As I'm sure you are aware, if you are running 170 to 180... you are right at the limiting operating temperature for PEX or PEX-AL-PEX.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 3,718
    If you are concerned about efficiency you should really insulate it. That will also protect it from UV.
  • saxsquad29
    saxsquad29 Member Posts: 8
    Is it okay to lower my max boiler temp to 150 on my non condensing boiler. I am getting about a delta 40 right now between return and supply with a max of 170 and return is right around 130. The boiler does shut off when it reaches the max and allows the circulator to run and that brings the return closer to supply temp obviously. Then it kicks on again at 150.
  • Jamie Hall
    Jamie Hall Member Posts: 16,651
    That low a return temperature for a non-condensing boiler will pretty much guarantee a short and miserable life due to corrosion. A much better arrangement would be to increase the flow in the main loop, to bring the delta T down to something reasonable, like maybe 20, then use primary/secondary piping to allow the boiler to run at a reasonable temperature for the boiler -- like say 170 or thereabouts.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • saxsquad29
    saxsquad29 Member Posts: 8
    Our boiler was installed in 1985, so it's nearing the end of life. Looking at a high efficiency condensing boiler. I have 1/2" pex al pex from the manifold and 1 1/4 near boiler piping to the manifold. Home run installation.