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Advice needed: Twin Boiler Gravity Conversion Heating System W/indirect Water Heater

First of all; Thank you, Dan, for "Pumping away", "Primary and secondary Pumping", and your fabulous article online about gravity heating. My 1909 system originally used the dining room radiator as the expansion tank: It has two bleeds, one top, and one on the bottom so you could establish an air cushion in the radiator. And the room was over-radiated to make up for it... (a second large radiator). The system has been heated with coal, then fuel oil, and, since 1985 with natural gas. Sometime ago, I got a good price on two high mass boilers that essentially split the heat load, and I have the Danfoss balancing valves as well. My plans to use the exsisting gravity heating loop as the primary circuit, with the two boilers connected to it (the secondary circuit) with reverse return on the boilers. I will be following up with a circuit plan, but I have many questions first: Should I plumb the non-gas portion of this with copper or steel? What are the pros and cons? I'm basically equipped to do it with either material. I lack experience with threading and positioning unions. I've done lots of sweating...
(I'm sweating a little bit right now, Winter is getting closer... Hee Hee) Also, It seems like the contractors in the Minnesota area mostly have no clue about "Primary-Secondary" Is there someone near Minneapolis that might be able to advise me as well? Thank you, Dale.


  • DCastleDCastle Posts: 6Member
    I'm sorry, I thanked Dan, but I'm welcome to any and all opinions from everybody. Thanks, Dale
  • Erin Holohan HaskellErin Holohan Haskell Posts: 1,216Member, Moderator, Administrator
  • Jamie HallJamie Hall Posts: 12,124Member
    Can you post a piping diagram of what you are proposing? And perhaps what is there? That will help...
    Br. Jamie, osb

    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
  • DCastleDCastle Posts: 6Member
    I didn't do a heat loss calculation because the house is un-insulated, and the two boilers are replacing one that was 2,000 btu smaller than the two that are replacing it. I figure with proper insulation, the larger of my two boilers would probably do the job, with one as emergency backup. The 575 edr heat loss was calculated by measuring the 9 radiators and using the correct old literature for the large column radiators. The reason for the lower seperate circulators is to avoid having the cold water from the primary return slowing the heating process of the domestic water. The water heater circulators need a controller get priority over the primary heating circuit. All the circulators have the built in check valves, and I can see (now after sketching this out) that I am going to have to add some carefully placed ball valves, boiler drain cocks and perhaps 1/2" lines so that I can purge the water heater and lower circulators first, then the upper circulators, bleed the air up top (drain cocks on the primary line), and then continue to fill the system. Maybe there is an easier way to plumb this.... The primary circuit circulator would run continuosly (turn it off in the Summer). Thanks, Dale
  • ch4manch4man Posts: 203Member
    what brand and model boilers did you get? your schematic leaves a lot to be desired.
    im in your area, i know of no contractor that will install a boiler they themselves didnt supply.

    why bother with primary/secondary if you house is piped in a single zone. a Taco SR502 i believe will give you priority control of the indirect WH
  • ZmanZman Posts: 5,529Member
    I like primary secondary because it allows constant flow to the system which will distribute more evenly. With the ESBE's, the output flow from the boiler(s) will vary.
    I think piping it something like this would be cleaner.

    There is , of course a bunch of stuff missing and little decisions to be made.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • ZmanZman Posts: 5,529Member
    I would also suggest a simple controller like a Tekmar 261 to handle staging the 2 boilers and running outdoor reset and DHW priority
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DCastleDCastle Posts: 6Member
    Thank you, so far.... Especially for the nice computer generated piping diagram, and the Tekmar advice. Problem is, I can't feed the indirect water heater off of the primary circuit... The primary circuit is a "battery" of 9 large radiators. It's like heating up a swimming pool. Thats why I have the Danfoss esbe's... And besides that, the primary circuit will be off (circulator and all) during the Summer. My goal is to have the primary circuit running continuously (turned off in the Summer), compare it to the way that old 1-zone baseboard systems worked... The water circulates continuosly, when the thermostat calls for heat, the burner on the boiler runs. It takes so long to heat up the primary circuit, I would rather not stop the flow. The other problem is I need 180 degree water for the water heater immediately. Thats why "my diagram leaves alot to be desired". And I would like to be able to heat the domestic water off of either boiler without opening an closing valves. I'd like it to be done at least electrically, if not automatically. Why am I using primary-secondary? Because from what I can tell, thats the only way you can have the load divided between two boilers, as opposed to just one. Google "Gravity Hot Water Heating-Old House Web". A great article by Dan Holohan... That's my starting point. As far as contractors that won't install a system unless they provide the boilers, not a problem, that's why I'm seeking professional advice. I don't need an installer for the install. The larger of the two boilers is a Weil-McLain CGa-3PIDN and the smaller one is a New Yorker CG30CNC-TE2. Thanks so far, keep thinking about this, I'll update you later with a better diagram. Dale
  • DCastleDCastle Posts: 6Member
    Almost forgot, it was asked "why do you need primary-secondary with only one zone? The indirect water heater makes it 2 zones...
  • ch4manch4man Posts: 203Member
    priority control on the indirect dictates its either the central heating or the indirect that gets full attention from the boiler(s) this can be piped parallel or pri/sec. heating the indirect happens in short order and done well before the central heating zone cools off
  • ch4manch4man Posts: 203Member
    to help you further as your tackling this yourself.

    read up on #1, #15 and #19 or all of them, its a great resource

    good luck
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