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Adding a zone on a one pipe system

ok, long story as short as possible. Currently, my house has a gas fired boiler heating two stories of radiators as one zone on a single pipe loop with mono flows. The house heats fine and my gas bills are low even with an 80% boiler.  I am finishing my attic to create two more bedrooms and a bath. It will have 4 radiators total. How would I create a new zone? Do I break the loop downstairs and just continue with a single pipe loop in the attic? Maybe control the heat with TRVs? If so, would I need monoflows on the attic loop? Should I just break the main loop into a two pipe system? I’m open to whatever would work best I’m just getting conflicting views from the pros I have looking at it now. The new loop, whatever it ends up being, will be in the attic floor system and upgrading or changing it down the road would be a mess so I need to get this part right the first time. Thank you all in advance for the help. 


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited November 2020
    Do not break the loop. If it is properly sized you don't want to mess with it.

    You will want to start near the boiler with a manifold large enough to handle the GPM of the existing loop plus the new GPM requirement of the new zone. You could try another Diverter Tee loop or you could do some other configuration like a parallel piping direct return system or a reverse return system.

    Just make sure the shared piping is adequate for both loops. I would use a separate circulator in your case. You can add a flow check to the existing zone while the system is open. the new zone can use the IFC version of whatever circulator pump you choose.

    Also, monoflow and TRVs don't play well together.

    Here is a text that may be helpful http://media.blueridgecompany.com/documents/ZoningMadeEasy.pdf

    I used it when teaching classes on the subject. Easy to read and understand

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,618
    edited November 2020
    There is a chart on shared pipe size on page 12.
    There is information about TRV and Monoflo tee systems on page 21
    And a good story on Flow Control valves on page 9 We call them Flow Check valves now, but sometimes us oldtimers still say FlowControl valves.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    EBEBRATT-Ed Member Posts: 15,353

    Keep it simple. Add another zone with it's own circulator at the boiler. With only 4 baseboards a 3/4" loop will do the job if your baseboards total BTUs are under 40,000 btu. Connect your new supply and return close to the boiler.

    Install a flow check valve on the new loop and put one on the monoflow loop if it doesn't have one. Some circulator pumps include check valves installed installed in them.

    Other than that do not disturb the monoflow loop
  • Dave T_2
    Dave T_2 Member Posts: 64
    Seperate 3/4 loop to new attic heat from boiler and back to boiler. Ideally you make it an independant zone with own circulator, tstat, etc.. You can how ever connect it to the existing supply and at the existing return just above the circulator, there by creating a 'split loop'. Down side of the split loop is you have only one thermostat in the house controlling everything - on the plus side it will be cheaper and if or when you want to make it an independant zone you can do everything at the boiler except running a thermostat wire to the attic. I would do the independant zone and you probably would want to either now or later. Good luck.
  • gracecon1
    gracecon1 Member Posts: 4
    Thank you all for your replies and I apologize for my late reply. It took me a while to unpack that article and understand it. It’s great, by the way. I will doing as advised and adding a separate zone at the boiler. I ordered a circ and a zone controller. I’m a plumber so I can burn it in but I have local help from HVAC pros to guide the install. Again, I appreciate you all taking the time to help.