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Heating old/new church

Solid_Fuel_Man Member Posts: 2,646
I'm looking at doing a boiler replacement at our church. It has a single Smith oil boiler. About 1/3 has fin-tube, built in the late 70s. The remaining 2/3 is radiant slab built in 2000. I'll get all the heatloss and radiation surveys this week. Total building is in the neighborhood of 700,000 btu/hr.

My initial thoughts are 4 mod/cons, propane is much cheaper than oil in large quantities in our area, almost all my commercial work is propane.

2 boilers for the low temp, and 2 for the fin-tube. Dont know if the advantages are worth it of making 2 separate systems. There are also 2 Axman Anderson coal boilers in a separate location, so those would need to be integrated making some mixing necessary. There is a single 2" 3 way motorized valve now which I could keep for the AxA boilers.

Just working on the preliminary stages of a heating plant replacement as the Smith has been around for 40 years and leveraging the low return temps of radiant slab with propane would save some money.

Trying to be proactive before they have to re-rope the Smith again.
Serving Northern Maine HVAC & Controls. I burn wood, it smells good!


  • Steamhead
    Steamhead Member Posts: 16,904

    Trying to be proactive before they have to re-rope the Smith again.

    If they have to re-rope that boiler periodically, something is wrong.

    We had one large job where the seals on a 28A-11 kept leaking. Turned out, the flame pattern was concentrated in the front of the boiler- and guess where the seals were deteriorating?

    This was a PowerFlame C-series gas burner, so I adjusted the head to produce a longer, skinnier flame- which also lowered the CO levels dramatically. So far, so good...................
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • gennady
    gennady Member Posts: 839
    edited October 2019
    Why not install the mixing valve with outdoor reset off boiler loop after take off for high temp, and use all 4 boilers in cascade?
    SuperJdelta T
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    It was re-roped 10 years ago, which was the first time in 30 years. It's a 19 series 10 section. Fired with a Beckett CF1400 @9.5gph high fire.

    I have little experience with commercial oil, just gas.

    I'm going to do a heatloss this week when I get the time.

    My thoughts with the low temp boilers was for efficiency, so at least two boilers would only need to make 120 degree water or less.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • SuperJ
    SuperJ Member Posts: 609
    I would probably put 3 400mbtu modcons in so you have one boiler for redundancy and cascade them as @gennady suggested. It'll be a lot cheaper to schedule the loops temperatures than to have two separate plants. You just need to plan it carefully not to lose your efficiency to high return water temperatures in the process.

    Run the high temp takeoff's and returns before the low temp takeoffs to take advantage of cascading temperatures. Some commercial boilers can run at 40, 60 or higher temp deltas.

    I'm doing a hospital now that has a primary loop with cascading takeoffs (sets of tees) for DHW, then snowmelt, then Zones(reheats), and finally AHU glycol. Temp deltas can exceed 80F. Return water temps are always in the 75-90F range.

    Boilers are 3 big Riello RTC 6000s.