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Heating System Retrofit

grrrdot Member Posts: 10
Looking to replace an old oversized boiler with a more appropriately sized mod-con. Additionally, the current system has performance problems; one zone too hot, one zone too cold and one zone just right.
Looking for some feedback / new ideas to improve performance when doing the boiler install.

This is in an old 1800 sqft brick row house, the building was gut renovated in the late 90's with an open floor plan so its laid out as three large rooms with a zone for each floor. Boiler is piped P/S with two secondary loops.
  • Bottom floor/zone is a Concrete slab with two 1/2" pex loops. It uses its own thermostat and gets 120F water. This zone works great.
  • Second floor/zone uses its own thermostat and is a mish-mash; a single large panel w/ TRV is in series with one loop of a two loop suspended 1/2" pex radiant floor. This zone is using zone valves to share the pump and mixing valve with the bottom floor, so it gets 120F water. This zone struggles to keep up and falls behind on colder days.
  • Top floor/zone uses its own thermostat and has three panel radiators all with TRV. Residents have to leave the TRVs wide open or the system makes a lot of noise. This zone has its own pump and gets full temp water, 175F. Feeling is this zone is always hot.
Doing a zone by zone heat loss calc and a lot of estimating for top floor emitters it should be able to keep up at ~160F, 10F delta.
So, thoughts on setting up the boiler something like?
  • ODR curve to 160F for design day temp (17F)
  • Top floor and second floor share a variable speed delta-p pump with two zone valves.
  • Bottom floor continues with mixing valve at 120F and current pump.


  • hot_rod
    hot_rod Member Posts: 18,177
    First assure that the amount of heat emitters can meet the design day heat load. At the SWT you are considering.

    It could b e the TRVs are installed backwards, they should be absolutely quiet.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream