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CI baseboard

I have had a local contractor come in and repipe our WM boiler, set it up with 5 zones w/honeywell ZV's.With the provisions for a mixing valve later as needed. I have done heat loss using the Slant Fin software and I was to install the needed fintube. Now with all that I have read here on The Wall, I feel that CI base board is the way to go. Question is, do I still use the same heat loss figures? In other words, is a BTUH still the same no matter what type of emitters I use? And I read a lot about constant circ. Is this something I should strive for for best comfort? My system will have adventually a combination of CI, floor warming in the tiled bathrooms/showers, towel warmer, and kick space in the kitchen and laundry room, poss. panel rad's in a glassed in porch that I feel that the CI baseboard won't carry the load. Slant Fin CI looks the best and makes my wife happy. Also will have the contractor come back to install a out door reset. Need any advice and what I should strive for. I am in a schorched air area and not many knowledgable contractors near by.


  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    is a BTUH still the same...

    ...no matter what type of emitters I use?

    Yes. In a "perfect world" the type of emitter has ZERO bearing on the heat loss of the space. Forced air however IS QUITE ABLE to produce pressure imbalances in a space that push conditioned air to the outdoors/unconditioned space and pull outdoor/unconditioned air into the conditioned space.

    Manual "J" calculations have a decent "fudge factor" built in, so they generally overstate heat loss--but the overstatement is consistent and that's what really matters. This overstatement is really only a problem with radiant panel heat in spaces with tightly-controlled infiltration. In that instance, non-standard (i.e. non-Manual J) calculations are often used to get a better idea of the "real" heat loss.

    You can achieve nearly constant circulation if your system is VERY well balanced and you use a tightly-controlled reset curve. The drawback to this method is that unless the reset control has an automatic "boost" function recovery from setback can be extremely sluggish. You also have to take return temperature into account and take any necessary means to protect the boiler from low return temperatures. For a reasonable idea of the "real" heat loss from a Manual J calculation use about 80-85% and use those numbers at various outdoor temperatures and the output tables of your emission device to get a reasonable idea of "actual" supply/return temperatures in the system.

    Proportional control (TRVs or pneumatics) are the only way I know to achieve true constant circulation. Installing them in a baseboard system varies in difficulty with the construction of the baseboard (to accommodate the devices) and the type of piping (loop or two-pipe).

    If budget allows cast iron it will [probably] produce a quieter, more comfortable and longer lasting system.

    In a system as you describe with baseboard, kickspace, radiant panel and panel rads be HIGHLY aware that the OUTPUT CHARACTERISTICS OF THESE DEVICES ARE GREATLY DIFFERENT!!! You have devices that "want" VERY little reset (the kickspaces) combined with those that "want" LOTS of reset (the radiant panels). In between are the baseboards (with iron "wanting" more reset than fin-tube) and the panel radiators.

    Since you already have zone valves you have "committed" yourself to digital control. TRVs won't achieve constant circulation in this case but can give somewhat increased control versatility in any area "zone" where used. I won't say that the TRVs would be a "waste" but you won't get their real benefit and your money will be better spent making a system that works efficiently and safely with your boiler and other "givens".

    Be VERY aware as well that your radiant panel and panel rad zones will likely have a quite small proportion of the total system load and may well result in a short-cycling condition that requires buffering.

    STUDY A LOT or find a GOOD contractor to get this system running!!!!!

    For whatever it might be worth, a piping arrangement similar to below would [I think] work well without low temp or short-cycle problems while still giving constant circulation and proportional control to the devices that can use them most. Alas though, no zone valves and some definite concessions regarding simplicity. Many omissions for clarity, circulator placement may not be ideal and variable speed injection could possibly be used in lieu of 4-way valve.
  • Unknown
    Can't really add much to that, Mike

    The output from the Cast Iron baseboard is similar, but not exactly the same, as residential fin tube baseboard.

    If we at Slant/Fin can help you further, call at 800 873 4346, which is our Technical Service (and my) number. I'd be glad to talk about your system with you.

    Noel Murdough

    Slant/Fin Corp.
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