Water line in attic?
user-980774
| Posted in General Questions on
Need to get a hot water line from one end of the house to the other in a ranch with a concrete slab.
Existing ranch has very low ceilings (7-8) so dropping any ceilings will not work.
No interior walls to use either. My plan is to run PEX thru the attic BELOW the insulation.
Water line would run over the top of the 2×4 bottom truss cord and I would create a tent over pipe so there was no insulation below PEX and R-40 above. House is in Colorado.
Any advice or code problems?
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Replies
Richard,
Q. "Any advice?"
A. Don't do it. I don't know your elevation in Colorado, or your minimum winter temperatures, but your suggestion certainly wouldn't work where I live in Vermont.
If you install the water line under the ceiling drywall, and enclose it in a chase, it won't take up much room or be very noticeable.
I don't know how you do things in the Autonomous Republic, but in most of New England the norm is to run 1x3 strapping parallel to the joists. Running a 1/2" water line in that space would not be frowned upon.
If you can run the PEX as a single continuous piece with no fittings in the attic or exterior walls, and you keep it close to the ceiling drywall, and you have a LOT of insulation on top of it, I don't see the problem. My experience with PEX freezing is that it's the metal fitting components that fail, not the pipe itself, and assuming the house is heated, I don't see how it's going to get below freezing directly on top of your ceiling anyway. Of course, if the power fails and the heat stops, all bets are off. Your plan to run over the top of the chords doesn't put the pipe that close to the ceiling, so I would revisit that.
Or, as Martin says, keep the pipe inside the house. I've seen it run down hallways behind crown molding.
Would the answers so far change if it were a conditioned attic? If he moves the insulation to the rafters and heats the attic, he's ok? I've often wondered why it's taboo to put pex in the attic. Is it colder than an unconditioned basement? Even considering the stack effect?
Stephen,
Q. "Would the answers so far change if it were a conditioned attic?"
A. Yes, of course. If the attic is conditioned, then the water pipe would be completely inside the home's thermal envelope.
I think that if the lines are under attic insulation, they are as warm as the conditioned space below. If not, by how much? 2d? 10d? I don't know, but how is it different than running pex behind caulked and sealed crown moulding?
David's advice is good, the PEX may freeze occasionally but ice plugs expand lengthwise at the disc of chrystal formation at the solid to liquid interface, not in circumference and no harm will occur unless the expanding ice plug can get a grip on a fitting and build pressure to push the fitting off. So long as the expansion can push back against an expansion tank or pressure relief valve at the water heater there will be no burst pipes. If you want to play it extra safe yo could put a pressure relief valve where the pipe re-enters the conditioned envelope it the other side of the house (or put a 2 gallon electric (Ariston, 120 volt) water heater w/ pressure relief at this point for "instant hot" under the sink or in an adjacent closet refilled w/ hot water from the main water heater)
You could even theoretically cross-connect the hot and cold under the sink with a pair of 3/8" stops shut almost all the way off and allow the toilet to serve as a pressure relief valve - ever wonder why cold water pipes freeze so rarely compared to hot water pipes? But I like the mini water heater solution better. In our rental we have it set up that way and we once accidentally unplugged the water heater and regular usage of the hot water kept the tank plenty hot until we spent a few days away from home and discovered the issue.
I'd recommend that you run 1/2" PEX in any event so as to reduce the wait time for hot water at the other end. Assuming that this is serving a single fixture group made up of water conserving fixtures you should have no problem with supplying adequate flow in 1/2" tubing w/ virtually no fittings. I don't run hot water in 3/4" lines unless as a home run from the water heater directly to a big soaking tub.
Richard, your plan is sound. With R40 above the Pex and the only barrier between the heated spaces below being 1/2" drywall there is no possibility of the pipes freezing.
Thanks all for the advice. I can't make the attic conditioned space and the line will run perpendicular to the lower truss chords, not parallel, so it will be 3.5" above drywall.
But I can run 1/2' PEX with no fittings and can create a tight tent and R-40+ above.
User980774 - how's this working out 10 years later?