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Buffer Tank or ??

Gauss79us Member Posts: 3
I moved into a home last spring; this past winter has proven to be very expensive, and I am wondering what I can do try and improve the efficiency of the heating system. Home was originally built in 1939 with hot water heat and A/C. Heating system consists of a boiler with two zones: Radiators and Hydrocoil. Hyrdocoil is integrated into A/C system. Zone valves are controlled by separate t-stats, tied together to activate boiler and pump. I have gathered the following:

EDR for radiator zone: 33k, estimated by best guess using all the knowledge on this forum.
Hydrocoil load: 62k

Boiler: Series 3 Burnham 140K input, with outdoor reset (factory settings)
Boiler run time: 7410 hrs
Boiler cycles: 98484

Boiler and hydrocoil are ~3/4 years old

An example of what I have witnessed: Hydrocoil t-stat calls for heat, run boiler, shutoff. A couple mins elapses and now rad. t-stat calls for heat, boiler restarts, runs, shutoff. And the cycle repeats.

Would installing a buffer tank help to reduce the cycling, and reduce the heating expense/wear on boiler? If, yes--am I looking at switching the zone valves to pumps as well?


  • leonz
    leonz Member Posts: 1,126
    Have you had the boiler cleaned and tuned up since you moved there??

    Have an energy audit done before you do anything else as improving the homes envelope
    will provide you a faster payback.

    Buffer tanks are usually used to store a great deal of heated water in solar panel systems that use parabolic sun tracking mirrors to heat the water.
  • Dave Carpentier
    Dave Carpentier Member Posts: 587
    Does the boiler short-cycle when it's feeding either load during a cold day ?
    If not, and this is just the case of when the alternate load appears causing a short time off duty, it's probably not a bad issue. Buffer tanks aren't cheap.
    But if you're getting short boiler cycles normally, then that could cause an early failure... so a buffer would help. The btu of your boiler vs the loads you figured would seem to indicate this.

    One method:
    In the buffer tank, you would have an aquastat that will wire to the boiler's TT terminals and likely control a primary circulator between the boiler and buffer tank. Now the boiler's job is to just keep the buffer tank hot, it doesnt care what's going on with load distribution.
    The tstats for the loads would open the load zone valves , and control your secondary (load) circulator. On mine, the zone valves have an end switch that control a relay which turns on the circulator. This half of the system doesnt care what the boiler is doing.. it's just taking water from the buffer tank.

    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • hot_rod
    hot_rod Member Posts: 22,120
    A heat load on the home would be a good starting point. How many square feet are you heating?
    A blower door test would show you where you have air leakage. Those areas can be easiest to deal with. Weatherstrip, sealing rim joists, etc
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 23,276
    Off topic, but a funny story. We are installing a large PV array at Cedric's home, and part of that process was getting an energy audit. Which was supposed to include a blower door test. When the jolly folk came to do the test, they took one look at the place... and the blower door test got tanked. Too many doors (19) too many windows (haven't counted) and too much elderly perimeter... they don't make a fan big enough!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Gauss79us
    Gauss79us Member Posts: 3
    Hi Leonz & hot_rod:

    The boiler was serviced right before I moved in. I pulled out some of the burner tubes and they look almost brand new. Flame looks great as well.

    The is a historic home and is roughly 4500 sqf. Is it leaky?: Yes. Could it use new windows?: Yes. Do I have to put back in custom made steel windows to match what is currently in the home: Yes (Thank you prior owners for getting it registered). I have spray foamed and sealed the walls & rim joists in one of the crawl spaces. I am working on cleaning up the electrical and plumbing on the other and will then spray foam the walls & rim joists in it.

    The loop with the fan coil is very short, maybe 15 LF total. Below is what I recorded a few weeks ago for a bit of time:

    27F outside, heating to 65F inside

    8:56pm off
    9:07 fan coil on
    9:08 boiler on
    9:14 boiler off
    9:16 fan coil off
    9:27 fan coil on
    9:29 boiler on
    9:31 boiler off
    9:36 fan coil off

    Thank you for all of your insights and help so far
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,840
    @Gauss79us this actually a well sized boiler it seems! That alone is great news. I can’t imagine a buffer tank would save any real money here. 

    7410 hours x 140kbtu input over 4 years? So about 2600 therms/year? Not cheap, but that’s a big house! 

    For your data, which admittedly is an extremely small sample size, the boiler ran for 8/40 minutes. That’s not actually that bad - you could play with the settings some to get that higher, 

    Be careful with insulation and air sealing: sealing obviously holes and going from 0 insulation to some insulation is sensible. But there are quick diminishing returns and it’s easy to pay much more per therm on insulation than you can buy a therm for. It’s not “low hanging” fruit. 
  • TonKa
    TonKa Member Posts: 104
    edited March 17
    Gauss79us said:
    Could it use new windows?: Yes. Do I have to put back in custom made steel windows to match what is currently in the home: Yes (Thank you prior owners for getting it registered)
    FWIW, if the current historic windows are in relatively decent shape, it would probably be significantly less expensive to perform long overdue maintenance/repair on the current windows and update them with spring bronze or bronze interlocking weatherstripping. If you then add internal or external period appropriate storm windows, you may find the insulating & air infiltration properties would now rival a new window.

  • hot_rod
    hot_rod Member Posts: 22,120
    We like to see at least a 10 minute boiler on cycle. And ideally at design conditions the boiler runs non stop

    Under 20 minute runs  leads to low cycle efficiencies. It could drive an 84% boiler down in to the 70% efficiency range
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream