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Near Boiler Piping for multi Temps

Jetman Member Posts: 4
Would like your input on the proposed piping diagram for a multi temperature design. This is a second home which I plan to keep at 45F when not in use. I would then turn on fan coil units several hours prior to arriving and then switch over to the more comfortable panel rads and radiant floor heat.
I have studied several different piping designs and settled on a Primary Seconary "Series" Loop. the system uses a conventional 3 sectional boiler.

Other alternatives consider were a Caleffi Hydraulic Separator ($$$) and a separate boiler loop with closely spaced Tees piped to the primary loop. I could not see the benefit of this adding another pump for the boiler loop over the "Series" Loop. My design data is shown on the sketch.

Any comments on the design would be appreciated.
Thank You


  • Zman
    Zman Member Posts: 7,328
    Overall, I like the design.
    If you are planning on keeping the house that cold, I would glycol the whole house to 30%+ and be done with it. This would eliminate a heat exchanger and a bunch of parts.It would also prevent the possibility of freezing the whole thing.

    I assume you plan on achieving the boiler minimum with smart mixing valves on the radiant and panel rads, that should work.

    The system will be at risk of short cycling a bit with all those panel rads. Some possible ways to mitigate would be: buffer tank, 2 stage boiler, a wide on off differential on boiler control.
    It is important to consider that outdoor reset reduces the emitter output and makes short cycling worse on warmer days.

    If this was my system, I would eliminate the fan coils and start the warm up period sooner using a home automation system. You could also set up the control side to sent hotter water to the rads and floor for faster warm up. Any system (tekmar and others) with indoor feedback will do this automatically when it sees how far behind the target it is.

    I assume the CI boiler is a personal preference. This would be a good application for a mod/con.

    I am not a fan of the boiler mate. Most other brands have more surface area in heat exchanger and are designed to reduce fouling.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Jetman
    Jetman Member Posts: 4
    Zman...Thank you for taking the time to look at the design. A couple of comments. Relative to the CI boiler, when comparing Propane to Oil including efficiency gains with the Mod-Con, Propane is 2X /BTU output in our area of NH, so I am sticking with Oil. Relative to Glycol, the Heat capacity is not as great as water and therefore requires more BTU's/lbF. For 160F and 30% mixture it takes 8% more BTU's, for 50% it is 15%. So I was limiting the amount of Glycol in the system.

    The Boiler Mate is existing so are the Fan coil units in the Air Handlers. I am using these now but really eager to hook up floor radiant and panel rad's. The house has a lot of volume and I turn on the air handlers remotely now and it takes about 4 hrs to go from 45 to 65F with outside air at 25F. Using the panel rads and radiant alone would take much longer to get the temp up in my experience.

    Good point about the cycling. I will leave a provision for a buffer tank.

    Again appreciate the comments, and wanted to give you a little more background on my thought process.
  • Paul48
    Paul48 Member Posts: 4,469
    Your boiler will short cycle itself to death, if only the panel rads are running. You're mixing the supply temps to the panel rads to 140, then forcing a 20* DT, but have 135* boiler protection.
  • hot_rod
    hot_rod Member Posts: 16,272
    A two pipe buffer tank would solve a few problems. It will buffer the boiler for small loads, and you have a lot of them :)

    It serves as the hydraulic separator.

    And it eliminates the temperature drop that you have with series P/S. Every time you connect another set of closely spaced tees you have a different mixed down temperature.
    With a two pipe buffer every load gets the same temperature, always. Mix down with motorized valves as needed.

    It could be less piping also.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,328
    I see the thought process.I did not realize the fuel option limitations and that some equipment was existing .

    Don't be confused by the glycol conversation. Just because the the glycol mix carries less BTU's/lbF does not mean you are losing the energy. You just need to move a bit more volume (higher gpm) to get the same amount of energy out of your system. I think glycol is good idea in a second home especially if you plan large temp setbacks.

    BTW, your are way ahead of most homeowners and many professionals on this.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein