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Convert gravity heat to pumped...or not?

Gasper
Gasper Member Posts: 148
Customer wants to replace their 1924 boiler. It is currently gravity hot water, and works well. My question is: is it best to replace with a cast iron boiler or possibly a copper fin, etc? Also, since the heat works well as is, should we convert to pumped? Or leave as gravity? Thank You!

Comments

  • Paul48
    Paul48 Member Posts: 4,470
    I wouldn't consider copper. Iron and copper don't play nice together. If you search "pin-holes in copper pipe", you'll find that some are caused by iron deposits. If gas isn't available, I'd stick with cast-iron. I'd also pump it, using Steamhead's data, available here. "Circulator sizing for gravity conversions". Because of the volume, if you don't pump it correctly, it will drop the most remote circuit.

    Disclaimer: I am a homeowner, with mechanical skills, but still a homeowner.
    HVACNUT
  • Gasper
    Gasper Member Posts: 148
    Thanks for feedback. I guess my biggest question is: why not just keep the system gravity? What is gained by adding a pump? The system works well now. Is it necessary due to the smaller water capacity of present day boilers?

    Using dialectric unions should solve the copper-black iron issue, if copper is used (pipe or heat exchanger). And adding a bypass should solve the temperature issue. Lochinvar Solution (as an example) makes a nice copper fin boiler, at a decent price.
  • HVACNUT
    HVACNUT Member Posts: 4,195
    Disclaimer: This is above my pay grade, without doing a week of research, but...
    I would think you'd definitely want to pump it. The existing boiler (just a guess) probably holds 3x the amount of water as a modern CI atmospheric boiler. That, with the large volume in the piping, I think you'd want to move it so you don't short cycle on limit.
    You might even need to pipe in a system bypass. Or boiler bypass. I forget which one.
    Real professional advice will be coming soon.
    Stay tuned.
    Paul48
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,290
    Stay with gravity. You can always add a pump after if you need too. Also install a couple of plugged tees in case you add a bypass (if you do put a circulator in).

    In my opinion adding a circulator to a gravity system that works well will only cause potential problems.

    Check with the boiler mfg. for any restrictions on using their boiler in a gravity system
  • JUGHNE
    JUGHNE Member Posts: 8,949
    I would consider the sizes and numbers of pipes connected to the old boiler.
    A lot of large openings in and out of boiler let the water move pretty freely. IMO....I have seen very few gravity HW and those without pumps did not perform very well.
  • jumper
    jumper Member Posts: 1,710
    Can a modern boiler work without a circ?
  • Paul48
    Paul48 Member Posts: 4,470
    I'd be concerned about the rusty water traveling through the copper HX. Mine is one of the countless gravity conversions that are out there. I put a Smith series 8 on the system. You have to look at the time that those systems were put into homes. There was no bang-bang boilers. You lit the boiler in the fall, and stopped feeding it coal in the spring. Provided you could achieve that with a modern boiler, I wouldn't want to pay the fuel bill.
    HVACNUT
  • kcopp
    kcopp Member Posts: 3,820
    I have done a few gravity conversions. 2 small, 2 very large. 2 gas. 2 oil.
    The key is to not over pump the system. Mimic the gravity flow to the system.
    The primary/ boiler piping should be done... properly sized.
    A robust mod /con could do vey well in this system.
    A good flush of the system would be in order and a magnetic separator a REALLY good idea.
    delta T
  • jumper
    jumper Member Posts: 1,710
    kcopp said:

    I have done a few gravity conversions. 2 small, 2 very large. 2 gas. 2 oil.
    The key is to not over pump the system. Mimic the gravity flow to the system.
    The primary/ boiler piping should be done... properly sized.
    A robust mod /con could do vey well in this system.
    A good flush of the system would be in order and a magnetic separator a REALLY good idea.

    Replace old boiler with same size pipe as original supply & return. Then circulated hot water from boiler feeds into & out of that bigger pipe. You need special fittings to prevent short circuit recirculation. The OEM circulator may be incorrect. You want required flow through boiler but the only pressure drop is through boiler itself. When big boilers were being replaced in seventies with multiple little ones that's how reps advised the piping.

    OTH I've seen old gravity systems with one floor being warmer than another. When new boiler with circ got installed directly piped into supply and return that problem went away.

  • newagedawn
    newagedawn Member Posts: 586
    do they have cast iron radiators, (they must), i just converted a 1900's gravity boiler to a buderus gas boiler with primary / secondary loops and used the grundfos 3 speed that came with the boiler on primary and used a taco true multi speed on secondary the radiators get hot in 20 minutes, the house used consume 1 tank of oil a month now a 250 gas bill a month with hot water ,stove, and dryer
    i did a whole house heat loss to get the numbers and built the system accordingly
    have pics if you want to see them
    truly my best energy saving job yet !!!!!!!
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
    Henry
  • HVACNUT
    HVACNUT Member Posts: 4,195
    @newagedawn .
    Yes, post pics.
    I love boiler porn.
    Canuckerdelta T
  • jumper
    jumper Member Posts: 1,710
    Pump salesmen love PrimarySecondary
    Solid_Fuel_Man
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    I'd convert to pumped with a modcon power plant.
    kcopp
  • AMservices
    AMservices Member Posts: 597
    Whatever you do, make sure you factor in some time rebalancing the radiators.
    Two years ago I help a customer that had his gravity system replaced the year after he bought his home. No attention was given to the radiators. his heat was extremely unbalanced and couldn't even reach the third floor.
    To fix the problem I move the pumps to the supply side of the boiler and replaced 28 radiator valves.
    Happy to say his system heats much faster and balanced.