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What to make of this weird piping?

mcscott Member Posts: 2
I'm in Western Washington State, so the heating season lasts from October till almost June, but its pretty much what most of you would consider shoulder season all the time; lows usually in the mid-high 30's except for four or five day's worth cold snaps where it'll get down to the low 20's. We'll often still need heat through May because it'll struggle to get to 60 during the day & get down to mid to low 50s at night.

House is 1950 1000 sq ft living space with a semi-finished mostly unheated basement of 680 sq ft that we're going to finish & heat in the next year or so. Monoflow, mostly fin tube baseboard & Trane Convector "radiators". IBC SL 20-115 modcon boiler.

The DHW right side makes perfect sense to me.

I'd love some opinions on the right side.

The ODR is sitting uninstalled with the boiler & its manuals.

The setup was explained to me thus:
"Because our temperatures are so mild and with such gentle swings, and because the system is using a buffer tank there's no need for the ODR. The boiler can heat the mass in the buffer tank and the system can call for heat as needed."

I'm by no means a heating professional, but it seems really weird to have two disconnected system like this. Why wouldn't you have the boiler control a circulator that pumps water *from* the buffer tank and around the house, and entirely do away with the circulator from the boiler to the buffer tank?

I'd imagine if that was the design then the ODR could be used successfully. What am I missing?



  • Alan (California Radiant) Forbes
    I would have piped it the same way including leaving the ODR out. Dialing in the heating curve on BB can be tough without significant savings.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • SuperTech
    SuperTech Member Posts: 2,186
    I would think that given everything you said regarding the weather in your area that outdoor reset would be a no brainer for energy savings and increased comfort.

    I would much rather see cast iron radiatiors or baseboards with that type of system. Take advantage of the mass and the fact that the radiators hold the heat longer and heat by conduction rather than convection. I believe these types of emitters offer superior comfort and less frequent cycling of the boiler.

    Are you using a single pipe monoflo system or two pipe?
  • mcscott
    mcscott Member Posts: 2
    Yup it's monoflow right around the perimeter. Kitchen has a radiator, I guess due to a remodel. Bathroom will eventually get a towel rack. It's just not cost effective to replace the rest of it much as I'd like to--and thermodynamics-wise know I should.

    Is odr really able to handle 60 for a high and 48 for a low which is what Oct, Nov, Mar-May look like around here?

    Nice to hear a fellow west coaster would have done it the same way! But why the two pumps Alan. And the tstat not controlling the boiler.

    And things'll most likely change once we do the basement. I guess there's the possibility to staple up radiant pex from the basement ceiling before we close it off.
  • Voyager
    Voyager Member Posts: 395
    mcscott said:

    Is odr really able to handle 60 for a high and 48 for a low which is what Oct, Nov, Mar-May look like around here?

    Nice to hear a fellow west coaster would have done it the same way! But why the two pumps Alan. And the tstat not controlling the boiler.

    ODR will handle whatever curve you give it. It may not make much difference with an outdoor range of only 12 degrees, but it should still work as intended.

    The two pumps are to give you a primary/secondary system. The buffer tank is basically the hydraulic separator or closely spaced Tees in a more conventional system.

    The thermostat controls the buffer tank circulator since the tank is effectively the heat source for the structure. The boiler is the heat source for the buffer tank and thus only needs to run when the tank temp gets below a certain setpoint, not every time the structure calls for heat. If there is enough heat in the tank to satisfy the demand of the structure, then no need to concurrently fire the boiler.

    Given your mild climate, the buffer tank may satisfy two or more calls for heat from the thermostat so why run the boiler each time unnecessarily?
  • hot_rod
    hot_rod Member Posts: 22,261
    It will work as drawn, assuming the return connections are near the bottom of the tank?

    There is another option called two pipe which helps eliminate mixing the tank with flow always going across it, it leverages stratification better and direct to load for quick delivery.

    If the tank runs at a high temperature, say 180, then ODR could work on the distribution side. It will reduce the mod con efficiency if you need high temperatures to cover the loads?

    Large connections on the tanks are required for 2 pipe.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream