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Mono flow delta P circulator or delta T circulator ?

mercedes Member Posts: 63
Cape style house with monoflow diverter valves original to the house. The house was expanded upstair and heated by baseboard and heat output is comfortable. After the conversion oil to gas boiler. The new boiler heat output on the monoflow first floor on cold days (15F) just make it ok but not great . The Heat Load Calculation shows 41K BTU loss (LoopCad software) the boiler DOE is 127kBTU. The feet of head 1.19 @ 2gpm on the monoflow first floor. A variable speed circulator would give me more play to get it right. So my question could I use delta P circulator (TACO VR1816) or delta T circulator (TACO VT2218)? The monoflow diverter tee is mainly controlled by pressure?
Thank you for any advice .


  • SuperTech
    SuperTech Member Posts: 1,671
    I also have a diverter tee system and I have used both the VT2218 and the Alpha 2 to pump my zones. They both can do the job adequately but I think the delta P pump is a little more appropriate for the application
  • SuperJ
    SuperJ Member Posts: 605
    edited March 2019
    ECM circulators are always good for energy savings (Delta P or T or constant curve).
    But Delta P only makes sense when you have changing flow characteristics, typically multiple zone valves.
    The Delta T pump makes more sense for a pure diverter valve system, but a correctly size constant speed pump could possible work just as well.

    Luckily both the pumps you mentioned have various constant speed settings as well as their fancier delta P/T modes.

    The infinitely variable adjustment on the VR1816 is may be more likely to fit your needs than the VT2218, assuming you system's operating point lies within it's curve.

    You have to pick one of four fixed speeds on on the VT2218 if you are in constant curve mode. If you want to use a variable flow mode delta T is the way to go for your system. But it's not always suitable and can have some undesirable interactions with outdoor reset curves.

  • hot_rod
    hot_rod Member Posts: 14,871
    Was the operating temperature changed with the new boiler? Does the boiler fire non stop on the cold days and not keep the home warm.

    To move heat energy you need temperature and flow, did either change with the remodel.

    Unless the radiation is zoned with TRVs or other, I think a fixed speeds the best option.

    ∆T circulator control needs these 3 conditions to operate as intended, Personally I think running fixed speed and modulating temperature based on outdoor and indoor feed back would give you the best control and efficiency.

    Some good reading about heat transfer in general here

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Gordy
    Gordy Member Posts: 9,514
    edited March 2019
    What was the original circulator before the changes? 2 gpm for the whole first floor mono flo isn’t moving much.
  • mercedes
    mercedes Member Posts: 63
    Gentlemen thank you for the response. Please forgive my grammar. My skill level is a beginner and I am learning about Hydronic Heating . The house renovation happened before I was asked to look at the heating issue. There was no Heat Load calculation done before the boiler replacement. The 2gpm I got was from the Hydronic Formula with a delta T 20F and added alittle. The Head loss I used the formula from J. Siegenthaler Heating with Renewable energy. So I develop a system curve to compare with a circulator. This is where I get lost and also with monoflow diverter tee's. I checked the radiators EDR from Dan Holohan page 216. The radiators exceed the heatloss on the main floor. Yes we have a new boiler and 2 new Taco 007 circulators one for main floor and other for upstairs. On the main floor monoflow is all original except the kitchen has floor heat kicker under the cabinet (fifth heat emitter on the line from the supply) and no monoflow diverter inline. The next inline is the bathroom radiator and no monoflow inline. One more radiator after this then return to the boiler.
    Hotrod: The boiler setting is at 180F. I will ask that question to the owner, if the boiler was running all day on the Zero degree temperature. I have Idronic #23 and will read tonight.
    Thank you.