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Redoing Dumb Hot Water Loop in kitchen (indirect, heat)

lewkewlewkew Posts: 6Member
Good news is I paid a flat price for the plumber to install an indirect hot water loop to heat the new 16'x14' addition (kitchen + mudroom + bathroom). Bad news is that the three radiators don't heat the space. I've done all the tweaking - opening buderus panel valves all the way (plumber had them half-closed), adjusting temperatures on indirect tank (triggers circulator at 175F, off at 185F), etc. Space is new construction, well-insulated. I've narrowed the problem to two solutions: 1) There is close to 5,000in^2 of tubes for this loop, because the dumb plumber didn't understand how surface area works and ran the hoses all the way around the basement... for fun, I guess, because it cost him $$$$ in supplies. I don't need/want the radiant heat from these tubes - if anything they're heating a different zone in the house, unhelpfully. I've measured and a much-more-direct 2,500in^2 loop is possible, but obviously that's a redo. 2) Other solution is to add another baseboard radiator to the loop, but if the loop is losing too much heat already then another heat sink won't be great ROI, not to mention punching more holes through the new tile floor. Or I could do both.

In mid-winter the loop circulator is on constantly, and can hold the temperature of the room but doesn't increase the temperature. If I'm cooking with the stove or oven that heat is enough to heat the room and it stays warm for hours and then the loop can hold that temp (running constantly). The three current radiators (1 6' baseboard, 2 buderus panels) measure a surface temp between 120F and 140F. So we're losing 40-60F from the indirect tank en route, and probably the same coming back. I've even spent $200 wrapping the tubes in insulation, which bought me ~25F at the radiators. But not enough. So frustrating.

Question: Do you think redoing the loop, cutting surface area in half, will be enough to bring the radiator surface temps up to ~160F? My arithmetic makes me think it will work, but what do people who do this in the real world think about this? ...I know math isn't always the answer. Thanks!


  • Jamie HallJamie Hall Posts: 10,550Member
    Shorter runs will help. So will better insulation. But... what is the flow through that system? And can you accurately measure the temperature going into the radiation and coming out? And are these things piped in series (one to the next to the next) or are they in parallel?

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • JellisJellis Posts: 121Member
    how long is the piping run from your boiler to the addition?
    the shortest possible path should certainly be used.
    what size tube is run to the radiators? if the tube is too small it will not allow enough BTU's to be delivered to the system.

    Some pictures may help. I cant imagine you would need another radiator for the space described.
  • lewkewlewkew Posts: 6Member
    Thanks for the reply! Current system has ~2,500in^2 of 3/4" tubing circulating around "old" part of basement (under a different heating zone of house), and a total of 2500in^2 of 1/2" in tubing runs off of the 3/4" loop going to addition, as well as (additionally) 1/2" tubing off the 1/2" loops to connect each of three radiators. Radiators are not in a series; these are connected as offshoots from the 1/2" loops. My "new" idea would run ~2,000in^2 of 3/4" tubing in a single loop pumped from indirect tank through to addition and back, with a total of ~500in^2 of 1/2" tubing off of the 3/4" loop to connect to/from each radiator - I can reuse the existing connections this way, and possibly re-cut the existing 1/2" tubing, so that my new cost is limited to the new 3/4" run.

    I think flow is not good right now, in addition to the long runs - I'm not an expert in fluid mechanics or anything but I can't imagine that a pump on the 3/4" loop is providing much circulation on the 1/2" loops that perpendicularly branch off, nor that the 1/2" connections to the radiators get much out of it.
  • JellisJellis Posts: 121Member
    yes sir, it sure sounds like your runs are FAR too long.
    Check out this article by Dan, it illustrates this problem nicely
    It would be best to run 3/4" to your Radiators, in as short a loop as possible. the addition should be a individual loop supplied from close to the boiler as you say. Your plumber certainly did not have a good handle on this.
  • lewkewlewkew Posts: 6Member
    I've made simple sketches (gifs) of current and proposed... let's see if this uploads...

  • STEVEusaPASTEVEusaPA Posts: 2,994Member
    Your last post mentioned a very important point that you previously didn't mention. That this is a water loop off of a steam boiler. Entirely different animal for the near boiler piping and controls.
    Need length of loops only, not sq ft.
    Need pictures of near boiler piping.
    Need to show controls used.
    Need to know circulator(s).
    Need to know type/size of tank and pics of how it's piped.
    Both sketches shown will not work at all
  • mikeg2015mikeg2015 Posts: 816Member
    Is the indirect also used for domestic water?

    Should be able to get indirect up to 160F with 185F water. Output if boiler circulator is sized right should be at least 50k BTU.

    So the problem must be flow rate on the load side.

    Need more temperatures and flow rates using pump curves. Best if you knew the pressures across the pumps.
  • mikeg2015mikeg2015 Posts: 816Member
    edited April 19
    lewkew said:

    I've made simple sketches (gifs) of current and proposed... let's see if this uploads...

    Is this a slab? Is the slab insulated under it? IS the slab perimeter insulated? How much insulation? Did you see the insulation installed. Is the ground frozen along the house in winter or does all the snow melt right next to the house for 6-12” away?

    16x14’ kitchen? that’s all? Is heat venting out a big kitchen hood all the time or something? Tight construction? At most you should be able ot heat this with maybe 15,000 BTU... assuming 3 outside walls, 1 exterior door and lots of windows.... unless they forgot to use any insulation... at all.

    SOmething is wrong with your indirect tank itself. Does it use a pump from the boiler to the indirect coil? Or just gravity flow? If just gravity flow, how big is the pipe?

    Let’s follow the BTU’s here. I’m perplexed.

  • mikeg2015mikeg2015 Posts: 816Member
    edited April 19
    Are you sure the system was bled of air? How was if bled? Is ther ea place to bleed the radiator and a high point on the floor loops? If all the connections are below there in the basement.... you have air. No pump will push air trapped in a loop. Flow will be minimal and heat transfer will be minimal.

  • ZmanZman Posts: 4,979Member
    edited April 20
    Pictures would help as would length of pipe.
    Sounds like a flow issue.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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