Separation between cold water line and heating ductwork

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by DavidTu, Feb 15, 2012.

  1. DavidTu

    DavidTu Member

    Messages:
    239
    Location:
    Seattle, WA
    The heating supply trunk line on a 38000 btu furnace runs down center of house. How close can we run cold water trunk (1" pex) as it must run parallel to it? Obviously we don't want to heat our cold supply.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,537
    Location:
    Cave Creek, Arizona
    If the heating duct is going to heat the cold water supply at any distance away, then someone forgot to insulate it. But, then, a 38,000 btu furnace is awfully small anyway.
  3. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    I wish water lines and ducts were insulated as they should be...but in the past insulation on such things has been surprisingly rare. It's not uncommon on new home builds to find whole sections of the attic, etc. that were supposed to be insulated, but weren't.
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,948
    Location:
    New England
    If you have access to it now, if it isn't insulated, insulate the ductwork and make sure you've sealed all of the seams so it doesn't leak. you can do the same with the water lines. Generally, that is enough. But, insulation just slows heat transfer, won't stop it.
  5. liquidplumber

    liquidplumber In the Trades

    Messages:
    69
    Location:
    Gastonia NC
    I dont think anyone actually answered your question. you could run that waterline INSIDE the ductwork if you wanted to. theres no code stopping you from running it next to it, inside it, 2, 10, or 20 feet away from it. As far as heat transfer from the duct work to the cold water, I cant imagine that unless you actually did run the line inside the duct that much if any heat would transfer to the water. And if it did transfer some small amount of heat.... what problem would that be anyway? I think perhaps you are over thinking on this. I cant see your specific situation, but i just cant even imagine how this could be a problem worth worrying about.
  6. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    You need to expand your imagination then. ;) Some of my water lines sit alongside the ductwork and the temperature impact on that water from the ductwork is obvious. If I could reach them without tearing out the sheet rock they would all be insulated...and sealed. The whole cavity is warmed or cooled and that includes the water in the lines. Makes for a toasty floor in the rooms above in winter...which is nice...but it also means that the air reaching wall registers is colder than it should be and the core of the house is warmer.

    What is far more problematic is to have supply and return air running side-by-side touching one another with no insulation between. We call that a heat exchanger, and yes, my system has that problem as well. Of course the idiots that ran the ducts also didn't seal the seams. Although the build was for the previous owner I talked with the co-owner of the business once, feeling out their knowledge: idiocy confirmed. When I replaced the AC unit, the new installers were in stitches over the humidifier configuration.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,537
    Location:
    Cave Creek, Arizona
    quote; the new installers were in stitches over the humidifier configuration.

    That is not unusual. Often when a worker sees something that is not done the way he would do it, he will make some comment about how it was done.
  8. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    True, but it was both ugly/overly convoluted/bulky and performing poorly. The new install re-oriented the existing humidifier and the humidistat. The new orientation makes fuller use of the pad (an astute observation on the installer's part) got rid of at least six feet of contorted metal ductwork (mostly swivel elbows) and a stupid looking hand fabricated metal box hanger on the wall. The difference in performance is night and day. An added bonus is that it opened up several square feet of floor space in the utility room.

    But the real icing on the cake is that it didn't cost me a dime. The rework was part of the new HVAC install and made use of the existing humidifier and humidistat.
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