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Replacing Large Low Hanging Boiler Pipes

I'm thinking about replacing the old low hanging 2" + pipes that connect to the boiler with PEX in the entire basement but leaving all the pipe in the walls that run to the radiators.  We want to get the space to drop a ceiling in.  I've attached a picture of our setup so you can get an idea of how the system is currently set up. 

I'm generally looking for anything I should consider or lookout for before starting this project.  I will be doing the work myself and have little plumbing experience but a very high attention to detail so I'm not concerned.  Mainly wondering if the new pipe which will be 1" or smaller will be change the flow of the system.


  • Gordan
    Gordan Member Posts: 891
    edited August 2010
    Sometimes the cost of perfection is too high

    Painting the pipes the same color as the wall, or hiding them in soffits, may be "good enough" unless the pipes are positioned in such a way that you'd be bumping your head on them all the time. Yes, reducing the pipe size by a half will affect flow, and also will affect the water content of your system (and therefore the length of the boiler firing cycle.) You've got what's called a direct return two-pipe system, so the effects of the reduced pipe size could be felt at the furthest emitter. The magnitude of this effect would be difficult to estimate without proper design.

    Really, if there's any way that you can be made happy without disturbing that pipe, you may want to consider it.

    Otherwise, you may want to consider a manifold piping scheme, where you run a separate PEX pair to each emitter's risers and hook them up to a manifold at the boiler. Manifolds are not cheap, however. Better ones give you the ability to balance the flow among various branches, but this still doesn't obviate the need to have a good design before cutting into existing pipe. If you're not comfortable with terms like "pressure drop" and "flow curve", you're better off leaving things alone (if they're otherwise working fine) or getting a competent professional.
  • Wayne Heid
    Wayne Heid Member Posts: 49
    Doable but ...

    Assuming we're talking about water, and not steam, replacing the basement headers with PEX is absolutely doable. However, as Gordon points out, there's more to consider than just pipe size. If you're serious about this project, you'll first need a heat loss calculation and radiator survey to determine the proper flow to each radiator. Using home-runs from a boiler room manifold to each riser, you may be surprised at how small the tubing needs to be. But you need to do the math first.

    There are other considerations such as boiler type and size, circulator sizing, pipe insulation, control strategy, etc.

    Unless you have hydronic system design experience, I'd suggest hiring a pro to provide you with a proper design before you break out the wrenches.

  • knockando
    knockando Member Posts: 3
    Responses to replies...

    Gordan - Believe me I wish I could just leave them or paint them but they hang too low in 50% of the area where finishing any space in the basement would be worthless.  I forgot to mention that they are wrapped in asbestos too and the cost to remove the asbestos from the pipe leave the the pipe would be 3x greater than cutting out the pipe leaving the asbestos. 

    Would the included picture work for my installation?

    Wayne - Yes, we are talking about hot water, not steam and yes, I have zero hydronic design experience :)  I will look into consulting with an area professional for the heat loss calculation and radiator survey.  Although I'm sceptical that we have anyone in the area that actually knows this and just doesn't pretend that they do. 

    If anyone know a hydronic professional in the western Iowa area let me know.
  • Steamhead
    Steamhead Member Posts: 16,832
    edited August 2010
    The A-word

    is a major red flag. In most parts of the country you need a licensed asbestos contractor for this work. Cutting the pipes and leaving the asbestos in place as you describe is probably illegal, and even it it's not, will release so much asbestos into the air that it could cause you or your family major problems later. Don't do it.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • tarro
    tarro Member Posts: 3
    similar problem

    knockando- Did you find anything else out, I posted a similar question today, not seeing yours first. I was wanting to do home runs with the pex and do a multi zone system. I saw a piece on This Old House were they did exactly that, but I can't find any info on specific designs.
  • knockando
    knockando Member Posts: 3
    Next step...

    We'll be bringing in a local hydronic heating specialist (at least they say they are) from a large plumbing company.  I will be asking him questions about flow rates to radiators and zoning but I don't seeing this project being a big deal at all, maybe I'm naive.  I'm thinking this would be a great time install some sort of zoning using a manifold.  Not sure on how I should go about installing a thermostat on the second floor though, if that's how it works.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    Where are you?

    Have you tried the find a professional page?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
This discussion has been closed.