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Residential Radiant Heating - Wirsbo Manifold/Balancing

JPG Member Posts: 3
I have a question about our residential radiant-heating system. We have two zones configured for radiant heat – the kitchen (first floor) and master bathroom (second floor). The kitchen loop is much shorter than the bathroom line. The rest of the home operates on forced hot-water radiators. The furnace is a Trio PurePro boiler and there is one Grundfos pump that services all HW lines. We have been here a few years and the radiant heat was installed by the previous owner. I have included pictures of the boiler and radiant-heat manifold.

The kitchen floor seems to warm up fine, the upstairs bathroom is slower to respond and generally does not get as warm as the kitchen. There is one thermostat in the kitchen that controls the two zones and both are activated when calling for heat. I don’t know anything about the amount of insulation installed in the upstairs bathroom floor.

The radiant hot water is distributed by a Wirsbo brass manifold with manually-operated balancing valves. Each zone (kitchen, bathroom) is set up on a separate 2-port manifold. For each zone, the supply line runs out to the floor and the control valves are located on the return side. A piece of PEX tubing runs between the supply and return line on the second port of each manifold. Both manifolds (kitchen, bathroom) are configured similarly. The picture only shows one of the manifolds.

We have been trying to balance the flow to ensure the bathroom floor is warm enough, especially important since cold weather is coming. The return line is hot when the thermostat is calling for heat and the flow is ~2-3 gpm (as per the meter on the Grundfos pump) for both zones. I flushed out the lines last year and don’t believe there is air trapped in the system. The manifolds do not have flow meters or temp gauges.

My questions:

1. Is there any reason for the ‘PEX jumper’ between the supply and return line? Can these ports just be capped off? I have tried to close down the adjusting valve to prevent flow in this line but not sure how tight it is. I don’t want to muck around with the valve cartridges as replacements are no longer available. Perhaps it’s just a by-pass line but not sure how it would be used, or if even needed.

2. We have a programmable thermostat and lower the temp during the day and raise it at night. For radiant heating systems, do folks generally set the temperature and forget it or can it be adjusted for day/night? I understand it takes longer to heart up these systems so perhaps it should be set at temp and left alone.

3. Given that the manifold is an older style unit, is there another type that would easily replace this one that would require minimal re-plumbing? There’s not a lot of play in the PEX lines so any replacement should be similar in size/dimensions to the original. It would be helpful if a new manifold had flow meters and/or temp gauges to assist with balancing.

4. Can PEX lines be connected/disconnected or is it a one-shot deal such that they that cannot be removed without damaging the o-ring/ferrule?

Thanks in advance for any help/advice you can provide.



  • Zman
    Zman Member Posts: 7,330
    edited November 2019
    1. It depends. I can't tell how the boiler is piped. Can you sketch it or take pictures from farther back and different angles?
    2. Just set it and forget it with radiant.
    3. That sounds like unnecessary work. If it turns out you don't need the bypass you could just install an adapter.
    4. If you take the tubing off the connector you should cut off the end. You can always splice another piece on.

    What mode is the Grundfos in?

    If you have fancoils and radiant loops off the same circ, that is probably the problem. The water is just lazy and goes through the fancoil.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • JPG
    JPG Member Posts: 3
    Thanks Zman, will provide more photos/information later tonight after work.

    The Grundfos is operating in the constant speed mode set to high. It is a model Alpha 15-55 F/LC

  • JPG
    JPG Member Posts: 3
    I sketched out the piping, let me know if you'd still like to see some other photos.

    The first diagram is of the HW feed and return lines.

    The second is of the manifold for the radiant heat in the kitchen and master bathroom. There are two of these manifolds (one for each room) and both are piped identically.