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Mod Con Buffer Tank for Short Cycling?

StewBrewer Member Posts: 10
I’m looking for some advice regarding the best approach to address potential short cycling I anticipate with my new mod-con, 11 zone, radiant underfloor plated + slab heating system.

I am concerned that the 17,000 btu difference between the boiler's minimum 18,000 btu output and 1300 btu load from bathroom floor radiant will result in short cycling.

If a buffer is the best way to go to address this problem, the calculations indicate a 30 gallon buffer would give me a 10 minute boiler run time.

Considering my primary concern is to prevent short cycling while getting the best possible efficiency from my mod-con, what is the best way to pipe this buffer (2,3,4); and consequently, what should control the boiler (buffer or thermostats)?
Mad Dog_2


  • kcopp
    kcopp Member Posts: 4,448
    Why 11 zones? How large is the house? Do you anticipate having that many different temps in the home?
    Mad Dog_2
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,917
    How likely is only 1 zone to be running? If the heat loss is 100,000btu/h, probably never. If it’s 30,000btu/h, likely. I don’t think you’ll ever make up the price of a buffer tank.
    Mad Dog_2
  • Dave Carpentier
    Dave Carpentier Member Posts: 604
    I use zone valves and the actuator end switches turn on the circulation (and by extension the boiler if needed).
    Disconnecting the end switches on my two smallest zones allows the system to ignore them when they are the only zone calling. Only when any other zone (with it's end switch still connected) starts the circ, do they get heat. The valves still open via a thermostat call, and still close once the room is warm enough. It/they just cant start up solo. The problem of a micro-load has been eliminated.
    Havent noticed the room(s) being colder than normal since I did this.
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
    Mad Dog_2
  • hot_rod
    hot_rod Member Posts: 22,476
    Sometimes those micro zones are bathrooms or kitchens that they may want to run year around. I ran mine a bit warmer than the AC temperature, although 78F is fine for me on the AC side.
    If so your system is a prime candidate for a buffer.

    One of the selling features of hydronics is unlimited zoning potential. And with mod cons that is easier than ever to accomplish.

    Cost would be the only downside of adding a buffer.

    Or use a high volume boiler like the HTP 55 gallon Pioneer, or the high mass Viessmann 300.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mad Dog_2Hot_water_fan
    EBEBRATT-Ed Member Posts: 15,839
    Over zoning adds to the install cost and then you need a buffer to make the job work.

    Why not do an accurate heat loss and put in the required radiation and put in fewer zones.

    Save money and be just as comfortable.

    Only if the microzone has widely different heat loss and you can't adjust for it with the radiation would you need to zone it
    Mad Dog_2MikeAmann
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,245
    All good suggestions.   Definitely could be over-zoned.  Hows about some pictures Sir?  Mad Dog