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Gravity feed system conversion

I have an old closed system gravity feed hot water system. I have a newer boiler Im hooking up and want to make sure I dont forget anything. The original boiler is a converted coal to gas boiler. There are 2 2" supply lines and one return. There is nothing in the attic that would make this an open system. It appears to be closed. There is a large expansion tank 3' by 1' in the basement and a water line with a regulator coming from the water main as a make up to top off the system.

Im going to put in one circulator pump a BG 100, and a bypass with two valves. The new boiler will be about 6' from the old one and Im going to tie into the 2" pipes with 3/4 " pipes from the new boiler.

I attached a picture of what Im planning on doing. Will this work or am I missinf something? Is there anything special I should do when I tie the 3/4 into the two 2" lines? I was goint to extend the 2" line a bit so I can attach the two supplies then attach the 3/4 to it

I read the gravity feed info on this site and I think Im about set but any extra info would be great


  • HenryHenry Member Posts: 965

    If you are a licensed and certified gas installer, I can provide you with what is wrong with your installation. Otherwise, I would advise you to use a professional that is lecensed and certified for the work. Besides the liability issues with insurance and litigation, it ain't going to work right!

    I just looked at a botched job near Boston on my way to RI. Gravity system conversions are very touchy!


  • midnightmoonlightmidnightmoonlight Member Posts: 9

    Im the owner of the property. From what I have read on this site it says to replace the near boiler pipes with a smaller size(divide current pipe in half then drop down a size), Install a bypass line and use a Bell &

    SERIES 100 circulator pump. The water line has a preasure valve which I will replace and the supply line on the 2" pipe has a compression tank. Is my problem connecting to the 2 supply lines? I was also going to a add an air separator if I find I have air problems. Everything Ive read on this site says its a fairly easy conversion. Is there a reason why you ccant help a home owner with info? Is this site only for licensed installers
  • Big Ed_4Big Ed_4 Member Posts: 1,340
    edited April 2010
    System Layout

    Post a diagram of the system layout , radiator piping ,mains and returns ..
    I have enough experience to know , that I dont know it all
  • midnightmoonlightmidnightmoonlight Member Posts: 9
    edited May 2010
    general diagram

    Problem is Im not at the house now and wont be until the end of the month. I have someone who may be willing to get that info. I tried a layout from my head but Im not 100% on how the lines go and I think it may be a waste without correct info.

    Do you need the exact layout of the supply and returns on the entire house?

    I attached a basic diagram but Im not exactly sure but its a general idea
  • SteamheadSteamhead Member Posts: 13,815

    obtain and post the amount of radiation (EDR) in the system. We can size a circ from that. Go here for more:

    You can make a larger circ like that B&G 100 work by throttling it with small pipes, but why? A properly-sized one lasts longer and uses less power.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • midnightmoonlightmidnightmoonlight Member Posts: 9
    Answers coming soon

    Im going to have someone on the other end of a phone at my place on Sunday.

    Im making a list of questions so I can cover any questions you have.

    Anything else thats important I should note please tell me.

    I will get the edr, and complete pipe layout (the best I can over the phone)
  • midnightmoonlightmidnightmoonlight Member Posts: 9
    edited May 2010
    Pipe and edr info

    Looks like I need a 20 GPM circulator so will a 27gpm be okay?

    All the info everyone asked for is on the updated diagram

    The new boiler supply and return are 1 1/4"

    Thanks for the help
  • HenryHenry Member Posts: 965

    TOO much circulator!! It is a gravity system so it has hardly any head. It should be piped a P/S. This will reduce the velocity in the gravity system while not cooling down the pre heated water going through the boiler when not running.

    Do it once / Do it right! Call a pro!

  • midnightmoonlightmidnightmoonlight Member Posts: 9

    What is piped P/S?

    This link reccomends 20gpm at 3.5' of head for the EDR I have

    Is there something Im missing on circulator size? The pump Im looking at is high flow low head. Shouldnt I go to 27gpm @ 3.5' of head opposed to 17 gpm @3.5 feet of head? There is no 20 gpm @ 3.5' of head. That Ive found anyway. Plus Im thinking of using the boiler for our hot water as well but thats another story
  • SteamheadSteamhead Member Posts: 13,815
    edited May 2010
    That boiler

    probably comes with a Taco 007 circulator. It should work fine on your system. It should be installed so it pumps away from the air separator/expansion tank connection and out towards the system.

    P/S is "primary-secondary" which will help keep the boiler from getting too much cold return water. You'd use the 007 for the system and a larger one like a 0010 on the boiler loop.

    As others have said, this should be done by a pro.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • midnightmoonlightmidnightmoonlight Member Posts: 9
    edited May 2010
    Why P/S

    Why would I use a P/S pipe system with a single boiler and one heat zone? Wont a by pass pipe setup address the return water temp?

    As far as a pro doing the job........ well as long as I own the house no one but my self will do the work....... period. Like putting a globe valve on the bypass in stead of a ball valve. I've accomplished alot of things in my day and this wont be left to a pottential hack. I have guys put new tires on my car thats it.....everything else I do...In fact I only bring them the wheels and tires. The car stays in my driveway

    I mean no offense to anyone here but I trust very few people with things that dirrectly effect my family.

    I have a few friends and another boiler professional I will be consulting in the morning.

    My bosses house was similar to the conversion Im about to embark on. Its an old coal gravity feed system that has been changed over to a pumped system. I talked to the company that did the work and they would set it up the same as my bosses house. This company has worked in the Boston area for generations and is a very good company.

    My bosses house has 2 large 3" supplies and one 3" return right up to the boiler with about 5' of copper bypass (with ball valves) and two large high flow low head circulators. Heats the house just fine.

    I want mine to heat a bit better then fine so Im doing the research and development now. Turning the wrench, striking the torch, and sweating are the least of my worries.

    A bit better then fine is my first goal. The second goal is to completely renovate the entire system and run the new flex pipe but right now is stage one and there is no money for stage 2
  • steve_26steve_26 Member Posts: 82
    Mix it

    Read up on mixing valves, Any time we do a conversion we use a 4 way mixing valve to bring the water temp more in line to the original design . Lots of water fed by a circ tends to over heat with rads. They were designed for 165 to 170 deg water. slow moving with gravity. now thow a circ in and they heat too fast. 4 way will give the boiler some protection against shock. use a outdoor reset get more comfort and payback.

    Good luck you may need it.
  • midnightmoonlightmidnightmoonlight Member Posts: 9
    Mixing valve

    Whats the benifit of a mixing valve piping setup compared to a bypass piping setup that would mix supply water into the return line?

    My main concern is pipe size from the boiler to the existing gravity system. Im going to tie into the 2" lines. My boiler has 1 1/4. Its my understanding I need smaller pipe around the boiler that then ties into the larger pipe. Calculations tell my 3/4...does that sound right?
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