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Has anyone re-piped a steam boiler for hot water?

anthmatic Member Posts: 2
I'm considering the switch from steam to hot water. I have two Smith 8 Series cast iron boilers currently running my system and I'd like to continue using those to heat hot water instead of steam. After reading the manual, it appears that they use the same boiler for both steam and water but they're outfitted a little differently to accommodate different controls needed. It looks like I can still find the parts that I'll need, save for the wire harness which I can make up.

Has anyone done this before? What might I be missing or not considering?

I know there are folks that prefer steam, but humor me...


  • Jamie Hall
    Jamie Hall Member Posts: 15,391
    OK, I'll humour you. Yes, those boilers can be used for a hot water system, and yes, you need a variety of new controls and piping.

    You will also need several pumps and valves and manifolds.

    You will also need to repipe some of the distribution system, if not all of it.

    You will need to check that the valves on the radiators are corret for hot water, and that the radiation installed can supply the heat you need for your space at the lower temperatures.

    You will need to remove all steam appliances -- traps, vents, maybe orifices, what have you -- from the system.

    If the steam system is one pipe, you will need to add returns to everything.

    You will need to pressure test the boilers and the piping and radiation at 30 psi.

    You will spend a lot of money and not be a happy camper when you are done.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 1,907
    1st WHY?

    What are you doing with all the steam piping? That's a lot of water volume to heat.

    What are you going to do about the lost BTU output of each radiator 1/3 - 1/2 drop.
  • JohnNY
    JohnNY Member Posts: 2,624
    Yes. I've done it. You can order the hot water wiring harness and control package for the boiler from the factory and it will contain the pump relay and all the other stuff you'll need. Outside the boiler, of course, you'll need to reconfigure everything for hydronic distribution. If you want to do it, don't be afraid of it. Assuming once converted it's the still the right boiler for the job, you'll be fine.
    Contact John "JohnNY" Cataneo, Master Plumber
    in New York
    in New Jersey
    for Consulting Work
    or take his class.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 1,819
    edited August 2020
    Assuming the emitters (radiators) are all ready for hot water circulation, you need to remove the supply and return piping and remove the gauge glass (and low float type LWCO if you have one) and remove the pressure controls. (Now that you have removed the "Steam Trim" you can start to set up the "Water Trim"

    1. Install on the supply side tapping a verticle riser.
    2. At this point, you may need a flow control valve if you are going to maintain boiler temperature for any reason. (like a tankless coil for DHW)
    3. Then you will install what is called a pumping away module. see diagram.

    4. You will need to change the relief valve from 15 psi to 30 psi. (CAUTION The rating plate for the boiler may not have the proper label for a 30 PSI relief valve. Some boilers are rated for both, some boilers are rated for steam at 15 PSI, and putting a 30 PSI relief valve would be a legal or liability problem. Mechanically there would be no problem since it is the same boiler for both steam and HW)
    5. After the circulator, the pipe goes to the emitter(s)
    6. On the return side (coming back from the emitter) you pipe to the return opening near the bottom of the boiler. No Hartford Loop needed. Just run directly into the return so you can drain the boiler and the emitter(s) at the same boiler drain valve.
    7. At the proper location, install a combination aquastat relay to operate the burner and circulator.
    8. Wiring should be straight forward. L1 and L2 are for power to the control after a switch from a proper fused dedicated circuit. B1 and B2 go to operate the burner. C1 and C2 operate the circulator. If you still have an LWCO then wire that into the circuit just after the B1 so as to keep the burner from operating if the water is to low for safe operation. If you do not have an LWCO then you might consider the Hydrolevel Aquastat relay with built-in LWCO. You will need the proper well adaptor.
    9. Now look for any opening where the steam trim was removed and not used. You will need to put a plug in any opening that is left.

    If you are using the same emitters as the steam system used, you are not yet finished. You will need to determine if they are compatible with water circulation. Not all emitters are. The above list is for connecting a steam boiler to a piping system that will accept a hot water boiler.

    I can see how this might be a project for someone with very little money that needs a new boiler and can't afford it. I would do this if I had a church or other charity ask for donations for one of the needy members. a few controls on a boiler that was removed from a home that recently converted from one fuel to another. The gently used boiler is in good shape and just sitting in the shop hoping for a new home.

    If you are converting the entire existing system.... the Steam Folks on this site will let you know the problems with that can be encountered. (don't do it) Steam is very forgiving of small radiator leaks at valves and swing joints. Water is not so forgiving. Steam traps need to be removed or gutted and drilled out. a second return piping system will need to be added on a one-pipe steam system. the list of problems goes on and on.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • jumper
    jumper Member Posts: 1,593
    My recollection of steam to HHW projects is that boiler is least of problems. Except that boiler is not rated for pressure above 15 psig. If authority allows you to re-rate boiler the requirement is at least static test at 150% of pressure you'll use. Why is same boiler okay for more than double the pressure for HHW than steam?
  • Steamhead
    Steamhead Member Posts: 14,341
    @anthmatic , why are you considering this?
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • anthmatic
    anthmatic Member Posts: 2
    Thanks everybody for all the info and insight. I really appreciate it and this does sound do-able if I choose to head down this path.

    One thing that I didn't mention is that if I went this route I'd remove the radiators and steam pipes.

    For everyone asking "why?": As my house has been improved / added on to over time, the heating system pretty much stayed the same. I think it would be too complicated to rework the steam system to work for my family. We'd also benefit a lot from having multiple zones. A few sticking points for me are:
    - At some point my house was split into two apartments (split down the middle) and the furnaces are set up the same way (this might have also been done to "follow the sun", I guess. So at this point, if I want to heat my entire first floor, I need to run both furnaces which also heats the second floor. And the opposite is true at night, if I want to heat the bedrooms, the first floor gets heated all night too.
    - There is an addition that was added at some point that has no heat and we'd like to heat it.
    - There are currently two sun porches that are being heated. I do still want them to remain heated, but at a lower temperature most of the time.

    As for the boiler pressure there is a label that suggests they're rated for 40 psi:

    but I agree that it makes sense to pressure test for sure.

    I can see how this might be a project for someone with very little money that needs a new boiler and can't afford it.

    @EdTheHeaterMan From what I've seen, I'm looking at around $ per boiler not including all the other stuff needed. If I can convert each over for < $, I'm saving $ which frees up the funds to put into other parts of the conversion. Let me know if that sounds too optimistic, though.
  • Zipper13
    Zipper13 Member Posts: 200
    If you want the upstairs and downstairs separately zoned and already have two boilers, have you looked into repiping the mains such that 2nd floor are on one boiler and first floor are on the other? Certainly, second and first floor radiators can be on the same branch in a wall which would complicate it, but I know that in my house, all radiators on both floors are separately branched and tied into the main directly in the basement. I suspect that would be a far cheaper option. I'm no pro, just a homeowner with a brainstorm on this.
    New owner of a 1920s home with steam heat north of Boston.
    Just trying to learn what I can do myself and what I just shouldn't touch
  • Jamie Hall
    Jamie Hall Member Posts: 15,391
    No prices. However, kindly allow me to assure you that you can't convert the boilers for the figure you mentioned and do it either correctly or safely. Indeed, you'd be hard pressed to find a competent person who even clean them and tune them up for that figure.

    A realistic budget for the complete removal (you mentioned radiators and pipes going out) of the steam system and installation of an all new heating system -- which is basically what you are talking about -- will be in the high five figures. To the left of the decimal point. If not low six.

    Further, for the level of work you appear to be contemplating, you should go back and do a complete, room by room, heat loss calculation and size the new boilers and the new radiation to that.

    Please do yourself a favour and don't try to MacGyver existing bits and pieces here and there into something which might or might not work. I've seen folks try to do it, and honestly I've never known it to work. Either do it right from the beginning, or don't do it at all.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 1,819
    @anthmatic said:
    @EdTheHeaterMan From what I've seen, I'm looking at around $ per boiler not including all the other stuff needed. If I can convert each over for < $, I'm saving $ which frees up the funds to put into other parts of the conversion. Let me know if that sounds too optimistic, though.

    I have been out to touch with the internet. I just moved from Southern NJ to Charleston SC. Internet turned on today.

    I see you found out that we don't post pricing here, so I did not get to see your actual $ amounts. I can see that you have a large project on hand. I agree that separating the steam system and reconfigure it from side-by-side to up-and-down would be a project. It would be best to start from scratch.

    If your current radiators are compatible with a water system, and they are of a size large enough to heat the space (Check this with EDR and Load Calculation) then you will need to start piping from the radiator back to the boiler on paper. As you add another radiator to the main pipe you can start to see how many BTUs are required in the shared (Main) piping. As more radiators are added to the Main the pipe size will need to be increased to accommodate the total flow BTU capacity

    This is a book that will help you to do just that.

    Once you have the layout you can start hanging pipes. You can use Copper or PEX with oxygen barrier, you may also want to build your near boiler piping with iron pipe and fittings to give you better support.

    Like the other herein, Do it Right the first time. The Wholesale price of a new package boiler v. the price of the components to make the existing boilers operable will save you something, but the wholesale price level, it won't be thousands. Maybe just one thousand plus or minus. Then there is warranty and liability for the old equipment you may be giving up

    Look at the big picture. Then see "if you are considering Air Conditioning..." There may be a lower cost furnace or inverter system that will provide you with the necessary heat for much less.

    The steam guys are going to crucify me for suggesting a "Scorched Air system" to replace a steam system. I have already reprimanded myself for even thing of such a mortal sin. Now I have something for Confession on Friday.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • Ironman
    Ironman Member Posts: 6,327
    edited August 2020
    If you're wanting to achieve different temps in different areas, then using TRVs is a much less expensive and viable approach. That way, the temp at each rad can be set differently. The thermostat would still have to INITIATE a call for heat, but each TRV could be set to limit the temp in each room. You would want the stat located in the coldest area.

    You also must realize that your piping and radiators have been operating at 2 psi or less for decades. Increasing that to 10 times that pressure which is where a hot water system operates at is asking for leaks. Something that will quickly ruin that system.

    Please carefully read what Jamie posted, it's spot on.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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