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Gravity hot water system

KingEdward
KingEdward Member Posts: 4
I have a customer that would like to switch from oil to natural gas.  They have 3 floors if  gravity radiators. The original tank in the attic has been disabled and there is a steel expansion tank in the basement ceiling.  It also has a pressure reducing valve.  Todays boilers only have 1 1/4 boiler tapings, I'm worried about adding a circulator if the house would not heat as even. I know i would have to add a bypass line or use primary/secondary piping. Should i consider using a steam boiler for the larger tapings converted to water and keep it gravity? The circulator in the photo was a basement zone and will be disconnected. 

Comments

  • Ironman
    Ironman Member Posts: 6,399
    We do gravity conversations frequently and also use a mod/con. They work great together if you know how to marry them.

    Don’t worry about the larger piping sizes: that was only necessary for gravity and pumping it won’t be a problem if everything is sized correctly.

    One thing to look for is orifice plates in the inlets of the upstairs rads. Remove them and put them in the downstairs rads. This is necessary because the flow dynamic has changed from gravity to forced flow.

    Have you done a load calc? That’s a must as well as a radiation survey.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    kcoppHVACNUT
  • KingEdward
    KingEdward Member Posts: 4
    Thanks for the comment,  I have read about the restriction plates you mentioned, i have not opened a union as of yet because the job is only in the planning stage.  I did see the valves are only 3/4". A heat calculation will be be done as well. I was trying to make  A decision on whether to keep it gravity or make it a pumped system.
  • Ironman
    Ironman Member Posts: 6,399
    Circulators aren’t that expensive and may actually help system performance.

    The gravity piping is 100+ years old. Over time, the interior of the pipes can become rough and smaller in diameter. That causes the flow to hindered and reduced. Converting it to forced flow eliminates that issue.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • I like the idea of keeping the gravity system and using the larger tappings of a steam boiler, but have never heard of it being done.
    Often wrong, never in doubt.
  • KingEdward
    KingEdward Member Posts: 4
    Converting a steam boiler to hot water isn't very difficult, basically replacing the steam pig tail and pressuretrol with an aquastat.  Replace 15 lb relief valve with 30 pound and gauge to T&P  Gauge. In my case i would not need to add on a circulator.  
  • mattmia2
    mattmia2 Member Posts: 3,429
    You only need to move enough water with the circulator to move the needed amount of heat which is far less than the maximum capacity of those pipes. I don't think the manufacturer would want to warranty a new boiler set up as gravity hot water. Pumped conversion is done all the time. I think there is an Idronics that talks quite a bit about it.
    KingEdward
  • pecmsg
    pecmsg Member Posts: 2,130
    One advantage of a circulator is being able to Zone areas. 
    Another is indirect HW heater. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 9,394
    edited September 10
    @KingEdward

    I would not go back to gravity now, it's forced hot water now. How does it heat with the existing boiler?

    I see at one time it had an HB Smith boiler, they left the old header in place @Jamie Hall

    Do a heat loss calculation. @DanHolohan tells how to do a gravity conversion in one of his books "How Come"

    I would do P/S no matter which boiler I installed.

    I would try the system without touching orifice plates first. Since it's already FHW it may be ok as is
    KingEdward
  • pecmsg
    pecmsg Member Posts: 2,130
    The house were living in HAD Hw Gravity system. I will say most comfortable / Even heating system I've ever seen. Also the most expensive to operate!

    Zone it
    1st floor
    2nd floor
    3rd floor
    Domestic HW
  • I would not go back to gravity now, it's forced hot water now.
    @KingEdward said, "The circulator in the photo was a basement zone and will be disconnected."

    As far as zoning an old gravity system, it's not that easy. One of those take-offs from the header at the boiler may serve radiators on multiple floors.
    Often wrong, never in doubt.
    mattmia2KingEdward
  • Zman
    Zman Member Posts: 6,712
    I say pump it. Buy an antique car if you want a fun project.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Ironman
  • KingEdward
    KingEdward Member Posts: 4
    @EBEBRATT-Ed Thanks for the comment, ill check out the book how come. The system is gravity now not pumped. The circulator is only on a disconnected basement zone. I wasn't interested in making it more that 1 zone. Im only looking for opinion on if it will still heat 3 floors evenly with a circulator.  Ed
  • HVACNUT
    HVACNUT Member Posts: 4,015
    edited September 11
    Primary/Secondary piping, constant circulation, TRV's, ODR, and a regular (STUPID) thermostat. 
    Is that a good combo?
    KingEdwardZmanPC7060