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Oil fired hot water boiler sizing

David2424
David2424 Member Posts: 4
Hi folks. I am replacing my oil fired hot water boiler and this site has been incredibly informative. I did the Slant Fin heat loss calculation at 64,000 BTU. I have a 3 zone 3000 sq ft home. 2 zones are forced hot air and one is hot water baseboard. I have a domestic hot water coil in the boiler and a electric hot water heater plumbed before the boiler. I'm thinking that hot water heater should be plumbed after the boiler ? I have a pellet stove in the house as well. I am looking at a Crown Tobago TWZ-065WC or a TWZ-075WC. Does anyone have an opinion of which will better suit me. Dead on my heat loss calc or the 75,000 BTU ?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,059
    I'd go dead on my heat loss, assuming it's reasonably detailed. And yes, the electric hot water should be after the boiler -- that way you are using electricity (expensive) only as a booster.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    David2424
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,305
    edited June 2017
    They are the exact same boiler, only difference is the nozzle and the settings. The 65 nets out at 70,k btu's and the 75 @ 79k. The extra btu's would help keeping up with a coil, but you have storage.
    I would go with the 65 set up. If it's not keeping up on the coldest day you can bump it up to the 75 set up. You can even bump it up to the 100 settings-but this is only with a Beckett burner (remove low fire baffle) or a Carlin. Riello's F5 is only recommended with the 75 or 100. You could call Riello and ask them about an F3. I bet it would work as a 65 or 75.
    I'd rather you didn't get a pinner and use a triple pass and either make your water heater it's own zone with a flat plate heat exchanger, or use an indirect. I feel using making/storing domestic hot water with this boiler is cheaper than making/storing with electric (unless you get some very low electric rates).
    steve
    David2424
  • David2424
    David2424 Member Posts: 4
    Thanks very much Jamie !
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,385
    Why not convert that electric HWH to a storage tank with a flat plate heat exchanger and circ? Or an aquabooster, wired cold start? Either of these would drastically reduce the idle loss, the largest waste of fuel in off season and shoulder months
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    David2424
  • HVACNUT
    HVACNUT Member Posts: 4,194
    Definitely choose a triple pass boiler. If your upgrading, choosing a boiler with a tankless coil really isn't saving you anything on efficiency. Like the others have said, a 4th zone with an indirect or flat plate heat exchanger is the way to go. You could add outdoor reset, and with a cold start aquastat you'll see more savings.
    A Buderus G115/3 with a Riello BF3 will give you the BTU'S your looking for and there are many others to choose from rather than a pin block. I think (but not 100% sure) the Energy Kinetics EK1 can be downfired, and is also a boiler I would research.
    With a new boiler and a lower stack temperature, you might find you need to install a stainless chimney liner.
    David2424
  • newagedawn
    newagedawn Member Posts: 586
    not a fan of tolbago's they are very hard to open up to clean, want a cheaper boiler look into williamson about the same price but way easier to open and clean
    i agree with hvac nut, if you can afford somthing alittle better get the triple pass you will save money on oil cosumption 4 surrrr
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
    David2424
  • David2424
    David2424 Member Posts: 4
    Great advice. If I make a flat plate heat exchanger as a 4th zone, what controls that recirculating pump ? Is the Buderus G115/3 a triple pass ?
  • HVACNUT
    HVACNUT Member Posts: 4,194
    Yes, the G115 is a 3 pass CI boiler.if you go with that boiler and opt for the Logamatic 2107, you'll see huge savings. A lot of guys here won't agree on the 2107, but I think its a hell of a control.
    You can get product literature at Buderususa.com.
    GrallertDavid2424
  • Grallert
    Grallert Member Posts: 524
    HVACNUT said:

    Yes, the G115 is a 3 pass CI boiler.if you go with that boiler and opt for the Logamatic 2107, you'll see huge savings. A lot of guys here won't agree on the 2107, but I think its a hell of a control.

    You can get product literature at Buderususa.com.

    I'll second that. It is a great control. Simple to operate and trouble shoot.
    David2424
  • bob eck
    bob eck Member Posts: 928
    Where are you located at? Check out the Trio oil boiler low water volume and it is a 3 pass horizontal cast iron boiler. You can buy it with a oil burner but for any reason in the future if you want to burn LP gas or natural gas all you need to do is to change the burner. I would install a indirect water heater for your domestic hot water needs.
  • David2424
    David2424 Member Posts: 4
    So I bought and installed the Buderus G115 and installed a flat plate heat exchanger on top of my electric water heater. I did not buy the Logamatic because I already had zone relays on the wall. I added a relay and recirculator pump. The Buderus came with a Fuel Smart Hydrostat and I assumed I could contol the flat plate heat exchanger with it. Now I'm scratching my head. I'm thinking I need a aquastat from the hot water heater to control it's tempature. Is that correct ? I don't see anywhere to install one.
  • HVACNUT
    HVACNUT Member Posts: 4,194
    edited October 2017
    No aquastat.
    There is a thermostat inside the lower access panel on the water heater, and probably a manual reset high limit behind the upper panel.
    Your going to have to change some wiring in the water heater.

    The electric water heater is no longer powered by 115v or 220v correct. It can't be.

    On top of the water heater is access to the electric.
    You'll have black and white if it was 115v.
    Black and red if it was 220v.
    Basically, you need to remove the common or neutral from the upper and lower heater elements and rewire the circuit in series through the high limit and thermostat, eliminating the elements
    Connect the low volt wires from R,W or TT on the switching relay and then connect (splice) to black/red or black/white on the water heater.