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Replace 3" cast iron mains with smaller copper

Dawsonh4
Dawsonh4 Member Posts: 12
We are in a 100+ year old home, 1500 sq ft per floor, 3 floors and an unfinished basement, with a new Bosch (ZBR 28-3) water boiler and Grundfos (29896341P1) circulation pump, attached to large (3" reducing to 1.5" at the end of the run) iron supply/return lines. These supply cast iron rads. Basement is heated only by the exposed heating lines. It all works fine at this point, reasonable heating bills, no concerns.

Time to finish the basement, so those low hanging heating pipes have to be raised to the joists. Would it be fine to replace the old cast iron 3" pipes with smaller copper pipes now that it is no longer a gravity system? How small could I go? Any other recommendations?

Thanks so much!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Yes... with this precaution. You will upset the flow balance between the various radiators. Can't help it. So -- you will probably need to add balancing valves.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Solid_Fuel_Man
  • bob eck
    bob eck Member Posts: 930
    if you are going to do this why not zone each floor.
    build a supply and return manifold for each floor and run from the supply manifold to each radiator and then back to the return manifold. with the manifolds you can then balance flows to each radaitor.
    can you get to each radiator supply and return in the basement?
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    I am not opposed to doing something like that. Each radiator supply and return is in the basement. What is the advantage to doing this? How difficult is adding balancing valves?
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    If you can get at the supplies and returns in the basement -- do do what @bob eck suggested -- zone the system with proper manifolds and balancing valves. That's not at all hard to do, and will give you all sorts of nice control over what gets warm when.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    Thanks Jamie. One thing that worries me is that all the supply/returns from the radiators are iron. I heard connecting to them becomes fairly difficult. Can anyone provide color on this?

    Also, are there any good "how tos" on what you are suggesting with the manifold and zoning?

    All the help is very much appreciated
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Threaded iron? That's no problem at all to connect to. Just takes a few fittings. Pex-Al-Pex, copper, whatever. If the ends aren't threaded, Megapress or equivalent.

    Once you get the whole thing hooked up, what you need is one supply and one return manifold for each zone, with balancing valves on it (check Caleffi particularly). A zone valve or zone pump for each zone. Pipe the whole thing primary/secondary of the boiler loop. Lots of guidance on that -- again, check Caleffi's offereings.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Ironman
    Ironman Member Posts: 7,373
    edited December 2020
    I'm a little afraid that we're making this sound a good bit simpler than what it really is - especially for a home owner. This would be a very extensive project requiring the skills, knowledge and tools to do it. We can help with the knowledge part, but no more.

    Something else to consider: what's gonna heat the basement once the large black iron pipes are removed?

    Also, the Bosch is already piped p/s.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • GW
    GW Member Posts: 4,691
    I agree not a cake job to run Pex to every rad or riser. Half the plumber dudes out there wouldn’t touch this type of job, I suspect 

    1 -1/4” should work for the capacity of the boiler you mention. 

    That’s a big system, hope your boiler is good to go. You may wish to install an FW200 in the living space and make this a constant circulation system, to reduce huge stand by losses 

    hope you’re gonna protect the boiler with big low loss header and dirt magnets and such 

    Bob the ZBR, you need to do primary secondary in the field right? The KBR has a cute little p/s option which I like a lot. 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Ironman
    Ironman Member Posts: 7,373
    Correct Gary. It has an onboard circ and the OP mentioned an external Grundfos, but IDK what model from the number posted. So, that would indicate it's been piped p/s.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • GW
    GW Member Posts: 4,691
    That’s the general hope anyway 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    Sorry for my arrogance. What does piped p/s mean?

    I was hoping to run some floor heating in the basement.

    Why do you consider the system to be "big"? And why wouldn't plumbers touch it? It seems simple enough.

    Not trying to make this out to be less than it is. Just trying to gain a better understanding.

    Thank you very much for the help!
  • bob eck
    bob eck Member Posts: 930
    No this is not the easiest job to do. 
    If the home owner does not think they can do the job it’s time to hire a professional. 
    Yes taking 3” black steel mains out of the basement will reduce the heat it was giving off in the basement. 
    If they want some heat in the basement they could install a 4th zone using Ecostyle steel wall radiators. 
    This is a job to do over the non heating season where there would be no rush to get the job done. 
    Also depending on how much 3” black steel pipe is removed in the basement the new system will have less water in it so the heat the boiler produces will get out to the radiators faster. 
    On the supply and return piping to each radiator if you can not get to the threads on this pipe you can use a Viega Megapress MIP or FIP adapter and then a Pex adapter. 
    Viega has a product called Fostapex. Fostapex is a Pex pipe with aluminum in it that works as the oxygen barrier. This tubing is great for this type of job. The aluminum in the Fostapex helps to keep the pipe from growing in length when hot water runs through it and it will not droop and sag when hot water is running through it. Fostapex comes in 1/2” - 3/4” - 1” size and it comes in 20’ lengths or 150’ rolls. 
    This is a great product. 
  • GW
    GW Member Posts: 4,691
    Hi Dawson p-s is primary secondary, it’s jargon we use. Post a pic of your boiler from 10 feet back and we can comment on how your boiler was piped. All small boilers should have some form of “decoupling the boiler” from the heating system. Unless the heating system is quite small. Plus it gives some separation from dirt and crud in the old system (different topic) 

    Big- the moment you say 3” mains, is the moment I think you have a big system (residential). That’s a huge amount of water, as is the steel and iron. Water is a mass and it obviously needs to be heated. Think of a large cast iron pot versus a small thin gauge steel pot. What takes more energy to boil your pasta? Once that energy is heated up you kninda want to let it keep going. That’s why “constant circulation” is popular with heating guys that pay attention to details. 

    East vs difficult- it’s not brain surgery but most certainly several steps up the skill scale. If you don’t have very costly tools such as Mega Press, you’ll need to “un thread” all the rads and risers. That’s a lot of work, skilled labor. If you start dinging and slicing threads by mistake, you can double or quadruple your work, quite easily. Even mega press isn’t a slam dunk- the pipe has to be pretty perfect (clean and smooth), and getting the machine in tight places is sometimes a pain. 

    Here is my boiler, notice the “jumbo tee” (my wording, you’ll get a funny look if you ask for this at the vendors) under the boiler. 


    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Ironman
    Ironman Member Posts: 7,373
    Gary, what type/brand of tubing is that coming off of the manifold?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    edited December 2020
    Thanks for clarifying. Below is [crappy] picture from 10 feet back.

    Understood the task isn't "simple". I will definitely be getting help from a plumber friend. Just looking to understand it myself before diving too far in.

    Again - all help and input is much appreciated!




  • GW
    GW Member Posts: 4,691
    Bob that’s Hydronic Alternatives. Between the wood decking and the basement and garage slab, I have a bout a mile the stuff.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • GW
    GW Member Posts: 4,691
    Yes Dawson you have a primary secondary there. Are you running an FW 200 control? If you flip that white little door down on the boiler, the answer is behind that door.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    Not sure what an FW 200 is, but here is a picture.

    Also wondering if there is a problem with having the iron pipes running to the rads being 1 inch while the supply off manifold is something smaller?


  • Ironman
    Ironman Member Posts: 7,373
    No FW200 there.

    A 1" line can easily carry 80k btus on a FHW system, which is the net rating of your boiler.

    Considering all the variables and the fact that you'll have to do something to heat your basement, you'd do well to let someone design it for you.

    Where are you located? There may be a pro on here near you.

    Or, you can contact @Steve Minnich on here.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    What are the benefits of the FW200?

    I am definitely having my local plumber help me. He has experience doing a manifold system and a megapress.
  • PerryHolzman
    PerryHolzman Member Posts: 234
    You will definitely loose your heat in the basement by converting the piping; and will need to add basement radiators.

    All I did was switch to a mod con boiler which ran lower circulating temperatures for all but the coldest days of the year - and remove the old boiler that acted as its own radiator in the center of the basement - and I now have basement heating issues (and in reality should add some kind of radiator to the system to add heat to the basement).

    I suggest that you get the Slant Fin heat loss & radiator sizing app (download it off of their site) and figure out how big of radiators you need to install in the basement.

    You can use very old stand up cast iron radiators to the most modern sleek European styles. But, add them if you want a warm basement.
  • GW
    GW Member Posts: 4,691
    edited December 2020
    Perry that's certainly not incorrect, but if the rads upstairs are yuge and the basement rads are 'normal', less good- right? Always a twist with this stuff. Any heat will be better than nothing
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • GW
    GW Member Posts: 4,691
    Dawson just google outdoor reset control. It makes your boiler smarter and save fuel ESPECIALLY your system, you have a huge amount of mass
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • GW
    GW Member Posts: 4,691
    Oh I don't see any dirt mags there- if your plumber man shows up you may want to improve the near-boiler piping a little. If the boiler pulls in some crud you'll be replacing it sooner than later
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Dawsonh4
    Dawsonh4 Member Posts: 12
    10-4. Thanks for the help!