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Sizing system

ECW Member Posts: 14
I need to understand more and may be second guessing my HVAC contractor; but ...  am I way off base on design load?

1000 sq ft single story cottage, on very windy ridge, built on posts, open crawl space, south shore of Lake Ontario;

planning on panel rads with manual actuators, outside reset, 4 zones/4 circulators, Triangle Tube Prestige boiler, 3/4" PEX, 120 or 140 F supply temp

R-40 plus, high density cellulose in the walls, in the low cathedral ceilings and in the floors; very well sealed and caulked (needs mechanical ventilation)

My contractor says we should size for 40 BTU/hr/sq ft. The Climate Zone rules of thumb for this area say 50 BTU/hr/sq ft design load. 

My personal calculations show a 30 - 32 BTU's design load is fine in all but the living room (large windows) but contractor says its better to oversize the demand and get bigger/more rads (emitters) and run at a low temp (120 F) supply for comfort, fewer temp swings and better, more even dispersion of radiation into building, less convection. 




  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    as long as it's your emitters

    and not your boiler that you are sizing for such a huge load, I'd agree.

    this is a solo 60 for the heat load, though, definitely not the 110.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • heatboy
    heatboy Member Posts: 1,468
    Why not one pump.........

    ............and thermostatic radiator valves and no thermostats?  Much less complicated.

    There was an error rendering this rich post.

  • ECW
    ECW Member Posts: 14
    complicated, overkill ?

    Oversizing was referring to the emitters (panels) and the engine will be the smallest Prestige. 

    I wondered about 4 circulators and thermostats, and it was explained that zone isolation (series piping, 3/4" tube, 4 small pumps with zone thermostats and actuators on each panel), would enable responsiveness yet mindless control and different setpoints for different zones. Building will frequently be left unoccupied throughout heating season.

    This might be an issue: Two of the zones are all the way around the perimeter -- so these supply/return runs are significantly longer than the other two zones. Those more distant zones have the greatest heat loss factor. Tubing runs are through my 8" Larsen Truss wall cavities (in the cellulose).

    BTW - Larsen Trusses were recommend to me on this Wall 10 years ago. Condensing boilers were hotly debated then. Things are calmer on this site these days.

  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited March 2010
    Panel Rads

    with thermostatics and use a Grundfos Alpha or similiar pump. If not thermostatics then zone with valves and use the Alpha as a system pump. I would use a radiant manifold, feed the rads with 3/8" pex, use thermostatics and the alpha as my system pump

    There was an error rendering this rich post.

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