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Thread: Insulating water lines in attic?

  1. #1
    Water system engineer riverside67's Avatar
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    Default Insulating water lines in attic?

    I'm building a single story home in Oak Glen, Ca. The plumbing for the home runs above the ceiling. My hot/cold trunk lines are both 1.25". The hot line is already insulated along with the recirculation loop.

    I am thinking about insulating the cold lines myself to cut down on the noise that is heard when water is running.

    Are there any issues I should be aware of regarding insulating cold water lines that are in an unconditioned attic space?

    My roof has radiant barrier sheeting and the ceiling insulation will be R-38, but there are a number of roof vents and we experience freezing temperatures once and a while throughout winter.

    Thanks for any input!
    Last edited by Terry; 12-26-2010 at 01:18 PM.

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    Plumber jimbo's Avatar
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    Ideally, the water pipes would be under the ceiling insulation, so they are mainly exposed to the house temp at the ceiling, more than the cold attic temp.

    Last edited by Terry; 11-02-2010 at 09:51 AM.

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    Water system engineer riverside67's Avatar
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    Some of the R-38 attic insulation may make contact with some portions of the pipe but it certainly will not "encapsulate" them.

    Should I be concerned about condensation on the cold lines if I was to insulate them in the attic space?

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    Forum Admin, Expert Plumber Terry's Avatar
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    You are better off to leave the pipes bare, and lay insulation over them like a blanket.


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    Water system engineer riverside67's Avatar
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    Sound control is the primary objective here...

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    Forum Admin, Expert Plumber Terry's Avatar
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    That may be the case, but when pipe in an attic is insulated from the warmth of the home, you will have a lot more to worry about then sound.
    Have you ever seen a split copper pipe in a ceiling? I've seen entire ceilings drop onto the carpet below.

    However, since you are in Riverside California, when does it ever freeze anyway?

    For sound, it's the attachments to solid objects where most of the sound comes from. Work on the attachment points, and it should help.
    Last edited by Terry; 11-02-2010 at 11:29 AM.

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    Homeowner Thatguy's Avatar
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    Quote Originally Posted by riverside67 View Post
    Sound control is the primary objective here...
    So you need some viscous pipe wrap material to damp out the sound but that also conducts heat, and then use the diagrammed layout to allow house heat to warm the pipe.
    Rubber is viscous but has 2000x the thermal resistance of copper. Depending on the heat capacity of the water filled pipe, incoming water temp. and the amount of time that the air is below freezing, it might work.

    This link is one step in the calculation
    http://www.engineeringtoolbox.com/co...loss-d_19.html

    Or, maybe someone makes "shock mounts" for pipes. This would prevent the pipe noise from being transmitted to the house frame.

    Your outside design temp. is right at the borderline, pg. 74 of the link.
    http://host31.spidergraphics.com/nra...ES-137_Web.pdf

    You could also use a t'stat controlled heat tape to warm the insulated pipe but then
    it's a lump sum up front plus a continuing very small cost for elec.
    vs.
    a lump sum up front for the non-elec. solution but the outcome is more iffy.
    Last edited by Thatguy; 11-02-2010 at 12:30 PM.

  8. #8
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Default Freeze protection for pipes in attic

    My under-slab copper pipes failed a few years ago, so I re-plumbed the house overhead with CPVC. There are 2 80' 3/4" manifolds with 1/2" branch lines for each fixture along the way. Thanks to global warming, "deep freezes" are becoming common here in central FL, and I'm wondering how best to prevent these pipes from freezing. I'd love to know exactly how long it would take for CPVC to suffer damage at low temperatures, but so far the Flowguard folks have not responded to my requests for information.

    So far, the "dribble water from all the fixtures" method has worked, but the new showers, toilets and washing machine don't dribble, and there are portions of the sytem that dribbling won't help anyway. In a really severe freeze situation, I can drain everything, but that gets old.

    I've looked at several "heat tape" - style solutions, but none were designed with a multi-branched system in mind. The most elegant seems to be the Easy Heat "Freeze Free" cable, which is self-regulating. In theory, it you could cut and splice the bulk cable into any topography you want as long as no leg exceeds 75' from the power source, but the Easy Heat folks insist on strictly linear application of the cable using only their proprietary fittings. It's also wicked expensive, but I'm leaning toward this in spite of the manufacturer's warnings.

    There are other pre-formed cable/thermostat systems that could be forced into conforming to my layout, but by the time you buy lots of short cables, the price is really outrageous. Operating costs for all these heat-tape approaches are reasonable, since power consumption runs only 2 or 3 watts per foot.

    Another alternative is simply to heat the attic to maintain a temperature above 32. I can get a used AC airhandler unit with, say, a 5KW heat strip, and just fire it up when necessary, using the branch circuit for the existing home airhandler. Or, I could divert the airflow from the existing airhandler to heat the attic instead of the living space. The price is right, but the operating cost is obviously higher than the heat-tape method. I already block the attic vents to restrict outside airflow through the attic, but the roof and attic aren't tight or insulated at all. There's a good argument for insulating the attic to some degree, since that would also be beneficial in the summer cooling season.

    The last idea so far is to arrange a continuous circulation through the entire system, via the water heater, to maintain water temperature above 32. This is pretty-much a nonstarter.

    Interestingly, I brought this problem on myself by adding insulation to the attic -- prior to that, there was enough heat transfer from the living space to keep the attic at a safe temperature, but no more.

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    Master Plumber Redwood's Avatar
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    Its a pity that the Florida plumbers don't feel the need to plumb like they do a little further north.
    The pipes would be run against the sheetrock ceiling with insulation on top and would probably work well for you providing freeze protection as well as cooler water in the summer.

    They didn't run lines up the outside of the house did they?

    I'm also not a fan of CPVC at all. If that stuff freezes its all over!

  10. #10
    Moderator & Master Plumber hj's Avatar
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    I have NEVER heard of using CPVC with a manifold. It sounds like it must have used an enormous amount of pipe and fittings. The only two ways to prevent freezing are to either apply heat to the pipes, OR keep the cold away by heating the area. We cannot tell you which is most expedient, and economical for you since we would have to see the situation first. Disregarding the heat tape manufacturer's instructions COULD create a hazardous condition, unless you treat EACH branch line as an individual section. Circulating hot water using a "retrofit circulator and its bypass valves" would keep the hot line above freezing, and would probably also help the cold, at least to the water heater, since it would keep the water moving, thus keeping it above ambient temperature. The problem with a manifold system, however, it that you would need "bypass" valves at EVERY faucet, or at least the ones that could freeze, unless you modify the piping.

  11. #11
    Master Plumber Redwood's Avatar
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    Who says moving water can't freeze?
    http://www.snopes.com/photos/natural/niagarafalls.asp


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    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    "Manifold" was probably a strong word to describe my situation. The hot and cold "manifolds" are just 80-foot long 3/4" pipes running the length of the house, with 1/2" branch lines going to each fixture or group along the way. Both hot and cold manifolds are center-fed above the water heater. Most branch lines go straight down from the manifolds, through interior walls, to the fixtures, but there are a couple that run about 10' before they dive down into the walls.

    The manifolds couldn't be run against the ceiling sheetrock for a couple of reasons: 1) the joists get in the way every 24", and 2) the pipes wouldn't have any protection from errant nailguns. They're about 12" above the tops of the joists. I did consider just blowing a whole heap of insulation over them, and may yet do that. The branch lines do run parallel with the joists, of course, and could be dropped down closer to the ceiling.

    CPVC is just about all they use around here, even in high-end homes. So far, everybody seems to like it, and freezing is not normally an issue. During the deep freeze of a couple of weeks ago, my attic got down to about 28 for a few hours, but my "canary" bucket of water I keep up there never froze over. I'm going to make up some 2' lengths of CPVC and fill them with water to hang up there (over the bucket) to see what happens. I have another canary bucket outside. On that cold day, when I went out at 5AM to pick up the paper, it was liquid. I walked to the end of the driveway, got the paper, and when I came back in there was about 1/8" of ice on it. When that last BTU leaves and triggers the state change, it happens quickly.

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    One who lurks Basement_Lurker's Avatar
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    That's a cool pic redwood.


    Quote Originally Posted by Mikey View Post
    The manifolds couldn't be run against the ceiling sheetrock for a couple of reasons: 1) the joists get in the way every 24", and 2) the pipes wouldn't have any protection from errant nailguns. They're about 12" above the tops of the joists. I did consider just blowing a whole heap of insulation over them, and may yet do that. The branch lines do run parallel with the joists, of course, and could be dropped down closer to the ceiling.
    Mikey, you have a standard trunk and branch system, and both of those reasons for piping in the attic space only point to laziness and inexperience. Pipe penetrations in lumber are protected now by nail plates. If the insulation had been placed above the piping, you wouldn't have this problem. However, since the insulation is below it, if you now insulate above the piping, you won't be solving the actual problem. Insulation doesn't stop pipe freezing, it only slows it down. If the flash cold storms are very brief, then sandwiching the piping in insulation might be enough to stave off freezing. And I don't think leaving an unmonitored heating device (not including heat tape) in an attic is the safest choice.
    Broken promises don't upset me. I just think, why did they believe me? -Jack Handy


    www.blackbirdkitchenandbath.com

  14. #14
    Aspiring Old Fart, EE, computer & networking geek Mikey's Avatar
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    Quote Originally Posted by Basement_Lurker View Post
    ... both of those reasons for piping in the attic space only point to laziness and inexperience. Pipe penetrations in lumber are protected now by nail plates.
    Guilty as charged, as least as far as the "inexperience" part, and you can add "panic" to that -- the overhead installation was done hurriedly, since the house was without water. As far as nail plates, an earier post implied that the pipes should be laid directly on the ceiling sheetrock, so they'd have to be mighty big nail plates.

    Seeing the cross-section drawings that jimbo and Terry posted makes me think I can come up with something like that, and move the existing system on top of the joists to allow insulating like that. The pipes were placed as they were to get them out of the way of existing AC ductwork, but it might be possible to move them to run in contact with the ductwork, and then wind up placing both the pipes and the ductwork inside the newly-insulated space, killing a couple of birds with a few rolls of fiberglass.

    Aside, I've been looking at heat transfer calculations for pipe. I'm still fussing with details, but I'm encouraged to find that the thermal conductivity of CPVC is on the order of 2,500 times poorer than that of copper, so the time-to-freeze should be significantly longer for CPVC than for copper.
    Last edited by Mikey; 12-26-2010 at 06:03 PM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    When power is lost, ducts conduct cold very well.
    I would keep the pipes away from the ducts. It sounds like a good idea when the heat is on, but pipes normally freeze when the power is out.

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