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Connect to Radiators with PEX

Dave Ewald
Dave Ewald Member Posts: 36
I have hot water radiators in a diverter tee system. It's a really rotten system now that short cycles and overheats, I think due to gravity circulation (although I haven't yet checked to see if a short is causing the circulator to run continuously). The Honeywell aquastat is designed to maintain a minimum boiler water temperature. Domestic hot water is a separate system. I was thinking of:

1. Adding a ball valve to the supply and one to the return to isolate the near boiler piping from the radiation.

2. Adding a Flo-control valve to the supply just to the boiler side of the ball valve.

3. Adding a check valve or Flo-control valve just to the boiler side of the return ball valve.

4. Moving the circulator from the return to the supply between the Flo-control valve and the boiler.

Since valves larger than 1" get expensive, can I reduce the diameter with fittings to 1" to use smaller valves? The boiler is less than 100k btu, serves a 1 bedroom house with 7 radiators on the single floor, using about 500 gallons of oil last year.

Later on, if I decide to repipe the radiators, can I use PEX to replace the piping below the floor, accessable in the unfinished basement?


  • Dont be in such a rush to get rid of your diverter tee system. They can work great when set up properly.

    I doubt your overheating is due to gravity circulation. These systems require a considerable flow rate in the main to divert water in the radiators. You might get some gravity circulation in the main but probably not enough to heat the radiators.

    Check your circulator and see if it is running constantly regardless of thermostat setting.

    What minimum temp is your aquastat maintaining in the boiler? Have you tried adjusting the thermostat heat anticipator setting to reduce the overheating?
  • Dave Ewald
    Dave Ewald Member Posts: 36
    No PEX

    I put the thread title in and then digressed while writing the previous post. I probably won't do anything to the system until winter's over - so I'm just brainstorming now. I had thought that PEX would be easier and less expensive to work with for repiping, but it would look out-of-place, and isn't all that cheap, so I'll probably use iron for repiping, if I do any. I had set the minimum boiler water temperature as low as possible earlier on, but it didn't correct the problem. Thanks for your response!
  • Contractor
    Contractor Member Posts: 41

    Look into FostaPEX. It's manufactuered by Viega. It has a metalic look to it even though it is PEX surrounded by a layer of AL then a thin layer of PE to protect it from rusting. Alot of guys in the feild are using this because it looks good, doesnt have much of an expansion factor and you can run 5/8" to the baseboards. Just an idea.
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