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Open system conversion concerns

SSmith Member Posts: 11

Been a while since I posted anything. I've run into a system I need some advice on! Downtown Denver home circa 1906, approx 4000 square feet. Basement, main and second floors, then attic. Gravity coal conversion. Cast rads throughout. Everything appears original! Except for a gravity type expansion tank in the attic that looks like it was added maybe 50 years ago.
Client discovers a leak in the ceiling one day, and it turns out in the attic is a mess of galvanized piping run low in the attic, under blown insulation about 12" above the plaster ceiling height. A hole had developed in a horizontal section, the pipe has failed to the point I could put my fingers through it.

I wasn't equipped to dig through all of the blown in insulation but from what I can tell, there is a galvanized riser branching from each radiator stack somewhere on the second floor. I am guessing there are six risers. At least four tie together at this leaky spot in the attic and run through the roof as 2" galvanized. Another 2" galvanized roof penetration can be seen across the attic. Someone tied in a Thrift No. 18 expansion tank to the galvanized mess using copper which is why I believe the expansion tank is not original.
Client is ready for a new boiler, which is the easy part and it should be done. The problem is closing up the system so that it holds water and works! Should I just sawzall off every galvanized riser in the attic, hoping the vertical runs aren't corroded to the point that I cannot propress on some steel caps? Do I need to rip apart the house on the second floor to find these atmospheric risers and plug it there? I want to keep the system pressure as low as possible, just enough to fill the rads on the second floor, so I don't expose the attic risers to forces previously unseen. What I don't know is if the entire system is piped with galvanized; which I have not seen before but may exist for all I know. I also don't know how or where exactly the riser connections were made. The other option is to repipe the whole thing, which is a problem with the budget and schedule and amount of destruction to the home, etc..

Any advice is appreciated! Even if you tell me to 'walk away'. I am a one man show here after all.-Sean Smith



  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,074
    edited September 2022
    Beautiful old boiler and very smart of you to ask these questions before bringing out the sawsall.

    Instead of an open system, what you have there is a gravity system - no pump. It relies on the density of water when it is heated to move the water around.

    I would leave all the risers there as they help keep air out of them system. Just fix the leak and terminate the group risers into one or two automatic air vents. The air vents have 1/8" threads on the Schrader valves that you can connect to and pipe 1/8" copper to the closest plumbing vent for drainage if they foul.

    Before you price the boiler replacement, search here for "Gravity Conversion" as there are certain guidelines for doing this.

    Here are some great questions and answers about gravity systems that Dan Holohan wrote:
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • leonz
    leonz Member Posts: 1,165
    edited September 2022
    Coming from a novice:

    Let us back up here a few yards please;

    1. "we" collectively do not know YET whether this system is a bottom fed gravity hot water system or a
    top fed gravity hot water system
    a. The open to air expansion tank should have a vent to atmosphere through the roof to a rain gutter or
    to a visible drain pipe in the basement.
    b. The other issue is asbestos and whether it is clad in asbestos which will require an asbestos removal
    company to come in and remove the asbestos cladding using the proper fresh air door airlocks with
    zipper doors in the basement and the HEPA air filtration vented to the outside of the home long '
    before the boiler before a new boiler and new pipe insulation is installed.

    2. The system needs work with the leak repair wherein a heavy duty pair of Fernco? pipe couplers could
    splice in a new section of unthreaded pipe to replace the bad one if space allows it or if there is room
    for a new pipe joint and couplers

    3. if this is the only leak it would be foolish to seal off the piping since all the radiators are intact and
    not leaking and the plumbing for the new open to air expansion tank is installed

    4. if there is no feeder and drain pipe rising from the basement that would fill or refill the system by filling the open to air expansion tank to the full point in the open to air expansion tank the water filler valve and piping was removed at some point and plumbed into a bottom filling system with no regard to the correct plumbing for the expansion tank

    If there are 2 sets of vent pipes going through the roof it should be corrected making it a one pipe vent rising from the open to air expansion tank.

    Whoever installed this system when the home was built knew what they were doing and sometime after it was installed someone worked on it without understanding how it worked and made it worse.

    The time involved would be better spent to just trace all the pipe in the attic space with a helper
    and two clip boards and flashlights to document every elbow, nipple, wye, tee, valve and riser so you know what is there and while your at it do a heat loss study the right way so you can size the boiler
    NOT forgetting the huge amount of thermal mass the homeowner is blessed with as it's just like very hot water in the water bank.

    The best thing you can do with a helper using two clip boards and flash lights is to see where every heating pipe is and see where it connects and diagram the entire attic and you should see where the tee for the original open to air expansion tank that was originally there and install a new open to air expansion tank plumbing it in the right way which will provide slow even heat for the homeowner as it was designed to do originally.

    The plumber that designed this system spent time in the basement mapping out the pipe runs to the first floor risers where he planned to park the all radiators for the first floor and the risers to the second floor radiators and the risers to the cross connections to the open to air expansion tank and the vent through the roof to the rain gutter.

    YOU may have mistaken a stack vent going through the roof for a boiler riser vent so keep thar in mind too.

    If that boiler is clad in asbestos you are going to have plenty of time to correct the plumbing and do it the right way it was installed in 1906 while the asbestos is removed and the boiler broken apart by the asbestos removal company.

    If worse comes to worse, you could snake a roll of pex from the basement to the attic to fill a brand new open to air expansion tank using a float switch and simply fill it from the top of the steam chest of the boiler with a small circulator feeding 160 degree water to heat the home letting it fall by gravity to the drop pipes in the attic and then into the living space and the drop pipes from the radiators will send the cooler water back to the boiler sump.

    JUST PRAY that a painter or painters did not remove the restrictor discs in the radiators and as a result make a mess of things by ruining the correct balance on this heating system where the first floor has the larger restrictors and the second floor has the smaller ones so the first floor is heated first and the second floor is heated last.

    Hopefully you will see plumbing that would have connected a radiator in the attic to keep the open to air expansion tank from freezing or a set of elbows with a capped Tee in the middle of them that shows you that the open to air expansion tank was heated with hot water from the basement hot water riser pipe.

    My thoughts anyway.

  • SSmith
    SSmith Member Posts: 11
    Thanks gents-

    Alan your link to Holohan's article helps a great deal- I figured there was such a resource out there somewhere.
    Leonz- you are correct on many points- the key is, like you said- not knowing if it is a top fed gravity system or not. I am inclined to say is is not, the main reason being every radiator is piped using the bottom connections only. And man I hope I am right...
    The boiler room asbestos abatement and demolition is always sub-contracted out to professionals and they would have that thing gone in one long day, maybe two.
    I am loathe to just repair the damaged horizontal section of pipe. If there is one failure now after 117 years chances are all of the galvanized in the attic has reached its service life. I'll be sitting to Thanksgiving dinner and get the call that another leak has turned up. I am also not keen on keeping the system open to atmosphere- even though it has worked all this time- due to the planned boiler replacement and keeping the new equipment (and the ancient piping) protected via closed loop.
    In the end you are correct- I need to map out the attic piping in detail, and potentially open up walls/ceiling near a radiator to confirm what connections were made for the attic risers; and determine if it is top fed or not. That will guide the repair/replacement decision.

    You are dead right about people working on this without fully understanding and befuddling the guys like me who come along. But that's why I'm here- to get your advice! I've got to head to work- but I'll draw up a diagram of what I'm seeing in the attic this afternoon.

    Many Thanks!

  • leonz
    leonz Member Posts: 1,165
    edited September 2022
    Good morning Sean,

    Taking a sample of the boiler water and testing it for hardness and acidity would be first on my list.

    If you do not mind my being a pain in the a$$ can you take a good picture of the existing open to air expansion tank any piping at the base of the tank and the vent pipe and upload it here?

    I would like to see pictures of the radiators and the piping to them BECAUSE you stated they have a bottom connection ONLY with "no other piping", That slapped me at first into thinking it is a steam system.

    A gravity hot water system may have a single drop and riser pipe connection with one end of the radiator or two pipe connections using unions and O-S diverter tees or with unions and one pipe connection on one end at the bottom and the other at the upper tapping on the opposite end of the radiator on the top tapping or vice versa with unions using an elbow If I have my "fittings" right.

    I candidly and really do not think you will have to rip out any of that beautiful horse hair plaster and lathe to find the ALL the piping as I doubt any of it is hidden in a wall anywhere as little if any insulation was used when that beautiful home was built and the heating system was installed.

    MY first thought would be to fire the system up after the repair and then look for hot spots to find all the piping with an infra-red thermometer to save digging through the insulation just to find it.

    If you have a helper your helper can diagram every fitting and union and pipe joint on a legal pad by
    using one sheet of paper for 1/4 or 1/6 of the diagram in the attic to map the pipe runs, the length of the pipe runs and all the fittings by measuring the size of the attics width and length to get a better idea of the pipe runs in the attic itself before you crawl around with your flashlight, clip board and hand held infrared thermometer.

    By doing this you can better see how the piping was laid out by the brilliant plumber that sat on a box in the middle of the basement before the first stick of lumber was cut for the basement ceiling joists.

    This is what will save you time because otherwise you will be distracted from finding everything pipe and fitting wise as you mark down and diagram the piping while holding a hand held temperature sensor and you may very well miss a wye, tee, 15 degree tee at the top of the hot water riser, reducing tee that could have fed the open to air expansion tank using a globe valve or cross fitting.

    It would also eliminate mistaking stack vent pipes for overflow pipes from an open to air expansion tank.

    Thoughts from a novice stupid kid.
  • mattmia2
    mattmia2 Member Posts: 9,828
    Be careful that you don't create too much flow in those radiators, they rely on the slow flow that the gravity system had for convection within the radiator to heat the whole radiator. If you over pump it when you replace the boiler the water will just circulate across the bottom and won't heat the whole radiator very well.
  • leonz
    leonz Member Posts: 1,165
    Thats why I suggested simply repairing it and fixing the past mistakes
    and not creating a pumped system as the radiators my not work well
    shed heat slowly as the system was designed to do.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    You want to install the new boiler in accordance with the manufacturer's instructions. And that will include a circulator pump. There are specific instructions for cast iron boiler that require a minimum 130° return water temp. to avoid flue gas condensation. If you are going with a more efficient ModCon boiler, then the large water volume will increase the boiler efficiency with much cooler water returning to the boiler over longer cycles as the outdoor temperature drops. They usually have a primary/secondary manifold in their instructions as one option. The circulation of the water thru the radiators are not usually a concern because the circulator you purchase for the "system circulator" can be an ECM variable speed model that works on delta P, or Delta T so the radiators will not experience the problem @mattmia2 is suggesting. If you are sure that all the radiators are bottom fed and returned, then I would disconnect/remove the attic piping so you don't get the Thanksgiving Day call.

    I hate it when a customer says that they should not need to pay for a service call on a new boiler of system when something that was not included in the job goes wrong. So I try to include everything that I have control over. Get rid of the "possible problem" pipes if they are not necessary. Put a bladder expansion tank in the boiler room and forget it.

    Just the opinion of an old fart with 40+ years of experience.

    Mr. Ed

    PS. That old coal conversion is awesome! I remember working on those old things with oil burner conversions. After a good vacuum cleaning, we would slap on another coat of asbestos furnace cement to seal the clean-out doors back up. It's a wonder I can still breath today.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 9,828
    edited September 2022
    I'm not sure that galvanized pipe is original either. Most very old steel piping I have seen has been black iron with galvanized showing up between the 30's and the 50's. I think the alloy in galvanized is different than black iron as well with black iron being more inherently corrosion resistant, so perhaps the galvanized is trashed from the oxygen introduced from the open tank.

    I think at very least you need to very clearly state that you aren't sure of the condition of the existing piping and are not responsible for it with the new boiler connected to it, like a separate line to initial.
  • WMno57
    WMno57 Member Posts: 1,383
    edited September 2022
    Non-trades homeowner here. 1916 home, 2 1/2 inch (nominal) gravity pipes, 1950 boiler, one pump, not pumping away, one air over water compression tank. Nothing in the attic.
    I disagree with @leonz suggestions. Mostly agree with @Alan(CaliforniaRadiant)Forbes although I'd try to sell the client on not having anything wet, or needing maintenance in the attic. Since this is Denver, you have cold, winter, and unconditioned space in the attic.
    There are two paths you can take. Mod Con (maybe 88% efficient) or Cast Iron (maybe 82%). The problem with ModCons and gravity piping is you have to know how to adapt the ModCon to the old system. @Ironman knows how to do this, and has some great threads on The Wall with excellent pictures. Much more complicated, and hard to do right.
    Simple solution is a Basic modern cast iron boiler with a pump. It will be much more tolerant of all the grit and rust that is in the 100 year old pipes and radiators. Easy to configure, easy to maintain, might last 50 years.
    You DO NOT want an open system. No one does that today. Air mixing with water causes corrosion. Heating water in the attic so it doesn't freeze? Not very green. Both climate change green and pocketbook green.
    Gravity circulation was nifty 100 years ago when homes didn't have electric. Today, those 100 year old pipes and radiators don't flow as well. Today's boilers (even the cast iron ones) are different also. Smaller passages. If you don't have a pump, you need to plumb the new boiler to the existing pipe with large diameter pipe. Large diameter pipe is expensive.
    I think the only debatable item is diaphragm tank or air over water tank. Since this is a high volume system, you will need a large tank (or multiple small tanks). Diaphragm tanks are available everywhere and require no maintenance. They last about 10 years. A single large air over water tank is much cheaper than a large diaphragm tank or several small ones. It might last 70 years. Downside is they require annual maintenance and are harder to find at a supply house. Whichever way you go, the tank(s) should be in the basement. Future service techs don't want to visit the attic, and it could freeze up there.
    If it were my house, I would pay you to open the walls and cut the risers off mid second floor. If you and your client decide to roll the bones and have water in the attic, I suggest you replace all the attic horizontals with Pex. Probably should be barrier Pex, although that might not handle freezing as well.
    I DIY.
  • WMno57
    WMno57 Member Posts: 1,383
    Agree with Ed and Matt, who are faster writers than I.
    Black pipe vs galv pipe. Both are steel as are most of today's fittings. Doesn't matter because Iron, Steel, Galv, or Black all rust when oxygen is present. My 100 year old black steel pipes and mix of cast iron and steel fittings have not failed because they see a mostly anaerobic environment. Any dissolved oxygen in the water separates out when heated and either gets directed into my compression tank or the radiators on the second floor (which I bleed occasionally).
    All the more reason to avoid open systems, and have devices or procedures for removing air from the system.
    I DIY.
  • leonz
    leonz Member Posts: 1,165
    edited September 2022
    My owning an old home in the last 44 years has taught me a lot.

    If a plumber is unwilling to go into a cold attic to check an open to air expansion tank, that tells me a lot. We have local plumber that will not work on hot water or steam boilers nor install them, that tells me a lot.

    A properly designed and maintained system will be pushing 170+ degree water from the basement through the radiators to the open to air expansion tank.

    With a bottom fed open to air hot water heating system the attic may or may not have a radiator next to the open to air expansion tank or the hot water riser will be plumbed with some care to pipe hot water into the base of the open to air expansion tank first before it drops back down to feed the hot water to the radiators.

    I had an open system that worked very well to heat my home using an open to air saddle tank prior to the plumbers installing my hand fed boiler wood and coal boiler. Knowing what I know now I would have made sure the open to air expansion tank was left in place and the system left as a closed
    manually fed system as it would have made my life simpler when my well failed.

    I have no doubt a smaller steam rated boiler with an H stamp could be used to replace the converted boiler in this case as the steam chest has no baffles as far as I know.

    At most a work order would have to be created to have the boiler manufacturer weld in the matching tapping sizes near matching sizes to the steam chest and boiler sump.

    Once the system is refilled and an open to air expansion tank is in use the only steel that sees oxygen is the steel above the water line and the vent piping through the roof that drains to the rain gutter or the
    laundry sink drain or the overflow drain pipe to the basement floor drain.

    The only time you add water is when you do not see water in the lower sight glass and you open the fill
    valve if there is one in the attic or open a fill valve in the basement and wait for the water in the open to air expansion tank to spill in the laundry sink or the floor drain which tells you to turn the fill valve off.

    A while ago we had a new member whose rectangular open to air expansion tank began leaking that was on the third floor of his home at the third floor landing of his home. The repair was done by him and the replacement with the new tank worked fine.

    It was a simple enough job for him to have a new double wall tank sheared, bent, soldered and insulated when the new one was made and reinstalled it where the old one was as it was plumbed with N.P.T. unions to allow simple installation and removal.

    Knowing what I know now I would have never let them remove my old open saddle tank it and replace it with a bladder tank as they eliminated the manual fill system and as a result of that it caused me many, many, headaches which I do not have now with the closed system and 30 gallon steel compression tank.

    It is simple enough to add water treatment to a system like this one by pumping in non-toxic anti-freeze like the Hercules Cryotek 100 used in many home heating systems.

    Judging by the piping in the basement the water in the system will not be kept in the system when the boiler is scrapped and broken up and the system will have been exposed to atmospere until it is refilled.

    As long as the right steam rated boiler is chosen and a non-toxic antifreeze is used along with de-ionized water or good well water they can use the open to air expansion tank system with a new tank, sight glass, piping, and fittings successfully as long as it is plumbed correctly.

    Until the piping is fixed and the new boiler installed and the permanent non toxic antifreeze is pumped in to the new boiler the system will be exposed to atmospere UNLESS every valve to every radiator is shut and the vent pipe if found is capped or plugged.

    There are gravity hot water heating systems that are still heating homes today that are over 100 years old requiring simple maintenance.

    Draining the system may very well end up exposing faulty radiator valves that may very well need to be replaced and stir up dirt and rust that will require that the radiators be flushed out to rid them of the dirt and rust particles by using hot water and possibly washing soda to help clean them.

    If the system is bottom fed the air in the piping will be bled out as each radiator is bled free of air and the system is slowly filled with water pushing the air upwards into the open to air expansion tank and out of vent pipe and leaving only the steel above the maximum water line of the expansion tank exposed the atmosphere.

    If the non toxic antifreeze is pumped in first and the water is then added the antifreeze is mixed in with the water and the mixture is tested for its antifreeze vale and more antifreeze is added if needed.

    Adding a circulator and bladder bag expansion tank air scoop and air vents would be a waste of money as the air vents would have to be replaced when they start leaking and any trapped air in the system is going to be a problem to get rid of completely and in my case the slugs of air stopped all the heat transfer in the past.

    My thoughts on a gloomy cloud filled day.