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Small loops or zones in hydronic system – your experience?

dalee | Posted in General Questions on
Does somebody have experience with small loops or small zones of radiant (hydronic) heat they can share?
The emitter panels will be constructed mostly in walls or ceilings.
I have some low load rooms.  For example, one of them – a bathroom – loses 380 btu/hr on design day.  It would be ideal if that room were on its own loop with a balancing valve or TRV.  But, I’m looking at a flow less than 0.1 gpm if I do that.  I know this is a low value so I’m concerned.
For those of you experienced with hydronic heating in lower-load houses, feedback on how this has worked out for you or any problems you’ve had is appreciated.  Thank you.

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  1. scsiguy | | #1

    My radiant floor system has 15 zones. The smallest zone is a bathroom which has 505 btu/hr of heat loss (at design temp 0F), with another 67 btu/hr added for ventilation loss (Zehnder ERV) and 191 btu/hr for downward loss to the first floor, yielding a total of 763 btu/hr. Design flow rate is .15 gpm. Both heating and cooling from the floor works fine. There is rockwool installed in interior party walls (including surrounding this bathroom) to improve zone independence — e.g. bedrooms 2-4F colder than bathrooms.

    Lower flow rates than for my bathroom should be possible with the correct type of balancing valve, but perfection isn't required. So long as your thermostat controlled zone valve or TRV can fully close, you shouldn't drastically overshoot your temperature set point.

  2. Expert Member
    DCcontrarian | | #2

    It depends on what your heat source is and what it can handle.

    There's no reason why you have to slow the flow down. The heat output is determined by the water temperature and the floor design, if you have a higher flow the heat output will be the same the temperature drop will just be smaller.

    1. dalee | | #3

      It's will be an A2W heat pump, 3-pipe buffered. The heat pump manufacturers all recommend a delta-T and I really don't understand the impact on efficiency if a loop returns with a smaller delta-T. (OK, it mixes and slightly reduces overall delta T to the tank and pump - to what effect?) Therefore I thought it was safest to have about the same temperature drop on each loop.

      1. Expert Member
        DCcontrarian | | #4

        With a buffer tank you'll be fine.

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