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Heatload and boiler pump

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mamuel
mamuel Member Posts: 8
in Gas Heating

Good afternoon. Got a heatload calc done on house for getting a new boiler put in sometime this year yet. Install guy is down and I'm not around so haven't discussed the details too much but just wondering a few things for discussion. Heatload summary shows total load at 46.5K btu total load. Includes basement that has built in emitters but isn't sealed and finished as well to retain heat so will be doing windows and such shortly). The calculation was done with design day being 0 degrees so most most of the time, around 20 degree winter. Just reading the summary photo i have with measurements and btu's and gpm, the GPM required on all emitters is mostly less than 1 gpm. What size pumps would i even consider with a boiler that is 50k or less BTU and such low gpm than usually what comes with pumps?

Screenshot 2026-07-07 153259.png

Comments

  • Steamhead
    Steamhead Member Posts: 18,731

    What type of emitters are you using (radiators, baseboard etc)?

    Is everything on a single zone? What piping will you use- series-loop, Monoflo, home runs to a manifold, type and size of pipe?

    All Steamed Up, Inc.

    Baltimore, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting

  • GroundUp
    GroundUp Member Posts: 2,530

    The resistance in the piping and emitters are 95% of what determines circulator choice. Flow rate and BTU are only a small piece of the puzzle

  • mamuel
    mamuel Member Posts: 8
    edited 3:54PM

    Everything is baseboard. I have to pull off the basement ceiling to trace and map out the piping but I assume series. I dont remember if its 1/2 or 3/4 at the moment. I'm overseas right now so will have to verify when i get back hopefully soon. I thought that if I split it up diagonally, then total length of emitter in both zones will be just over 70ft (which i think is ideal max lenght?) so I was curious on doing zones that way or just have them parallel but 1 zone if that works. House isn't large or anything. Was suggested a HTP or Loch Knight 55kbtu mod con for the turndown. Even know its high temp emitter, shoulder season would help with modulating at least.

  • hot_rod
    hot_rod Member Posts: 27,901

    Fin tube generally designs around a 20° delta. A 46,500 BTU/ hr load would require 4.6 gpm of flow. Seems odd that the fintube lengths are in inches. Add them all up, 65- 70" of 3/4 fin tube is about max on one loop.

    3/4 fin tube will have a low pressure drop so most any of the common residential circs will work Grundfos Alpha 15-58, Taco 007E, etc. I like the newre electronic circulators, especially if you have multiple zones.

    The Knight comes with a variable speed circulator for the boiler itself. Usually that boiler is piped with a primary secondary of better yet a hydraulic separator.

    Download the installation manual for the Knight, or other boilers you are considering, for their suggested piping options.

    As for piping the fin tube, series, or individual home runs are a couple options. Depends on how many zones you want? Fig. 6.2 shows a home run with pex runs to each fin tube. This allows every room to have it's own temperature control, which may be overkitt for your project. But home run allows you to add zone control later on.

    I would suggest at least an upper and lower zone for best control.

    Screenshot 2026-07-07 at 10.32.40 AM.png Screenshot 2026-07-07 at 10.31.52 AM.png
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream

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