PEX: clamping for winter draining

I haven't found any detailed info on laying out PEX for a system that can be gravity drained for winterizing. Any tips from those who have done it, or any links?

I'm mostly interested in the long trunk runs. I'm planning a hybrid remote manifold system with two, 20' long, 3/4" runs to manifolds at fixture clusters, all in a crawlspace. I could cut progressively thicker shims and use those at joists to space j-hooks lower and lower, but I'm concerned about the PEX drooping between clamps and retaining water. If I use clamps at closer intervals, I think it will make it harder to use pipe insulation effectively.

The only alternative I've come up with is to fabricate a constant slope substrate to fasten the PEX to. Possibly something as simple as a taut guy-wire. The PEX could be fastened to that simply with a spiral wrap of tape, and insulation would wrap around the entire package nicely. However, it's not exactly conventional, and I have no idea if an inspector would approve.

Regardless of the method, I'm also concerned about how to leave slack pipe for expansion/contraction, while maintaining a constant drainage slope.

--David

Make a provision to connect a compressor to it and blow it out like they do to an irrigation system?

I've considered that, but the winter use for this cabin involves isolated weekend trips where we fill and then drain the system a few days later. I don't want to have to haul a compressor along each time, along with food and winter recreation gear, or invest in one to leave there full time--that would negate some of the savings of PEX over copper.

Speaking of which, I've also considered just rebuilding it with copper, which is very easy to design for draining. The current system, with the exception of the water heater (below the level of the drain exit), can be completely winterized in about 15 minutes, including antifreeze in the traps. Starting it up is even faster. That makes it very conducive to weekend use, and I absolutely want to retain that. But copper is not as easy to retrofit, of course.

Option 3 would be a true hybrid: straight copper trunks to fixture clusters, and PEX from manifolds to fixtures. It would be much simpler to ensure drainage on the short, mainly vertical runs from manifold to fixture. I'd lose some of the benefits of each system, but it would be easy to use and easy to install.

Are there no better options than that or blowing it out?

I would use a main trunk setup (like copper is run). As long as all of the horizontal runs and at a downward slop all you would have to do is open the drain and you would be good to go. Well open all of the futures, the drain valves, and dump the hot water heater.

There can still be water in the pipes when it freezes but, with out getting into a bunch of info it can only be so much.

Currently I open all of the fixtures to purge the pressure tank, and then open the drain--quite simple and fast.

I'm assuming that a pipe that's less than half-full will have no problems. But over half-full, I'd have concerns, since the expansion would exert force outwards against the pipe walls before it would even begin to buckle the solid surface of the ice into the remaining air space. Not a gamble I want to play with, particularly. For a 3/4" pipe, I can only have a dip of 3/8" between the low point of a span and the next lower clamp point, before the pipe will retain water to the halfway full point. For a 1/4" per foot slope pipe clamped on 16" centers, it wouldn't take very much--just under 3/4" of dip between clamps. Of course if I double the slope, I can tolerate a lot more dip...

But I haven't worked with PEX at all yet. How severe is the shape memory for straight runs?

As long as the pipes are only 1/2 full of water at the dips when it freezes you should be ok. At all of the joints you need to make sure there is no water. The only thing I would be concerned about is when you turn the water back on and all the ice starts to flow.

I started to reply to this the other day, then lost my connection... I was going to say something along the lines of, if a compressor's out of the question, like a cabin in the woods or something (hey, I was right! lucky guess...), why not just run it in copper?

It's a judgment call, but it seems to me that by the time you get done jury-rigging some system to hold the pex without dips and still have enough slack for expansion/contraction... the extra time & hassle will outweigh any savings.

Reading the tread now, I would add, this way you won't be worrying about it, either. You sound less-than sure... peace of mind is priceless.



Side-note: there's been some concerns about biological buildup ("bioslime") with PEX, mostly because the old rubber pipes had that problem. So far, it doesn't look like there's any cause for concern, in a normal system that gets used regularly... but in a 2nd home, that sits un-used a lot, I'd feel better with the slightly biocidal effect of the copper. The water puddle in those dips, with nothing stopping germs from breeding, for weeks at a time, would worry me.

To kill the bigger dips just run a steel line and toss a turn buckle in it. The get out the tape and tape the tubing on it.

Thanks for all the ideas!

I hadn't thought about the water sitting there supporting a little ecosystem--since it's well water, that's more of a concern than if it were treated. Hmm. Peace of mind is, if not priceless, worth more than the price difference (about $150, at a rough estimate).

The turnbuckle/guy-wire idea was exactly what I was thinking of. Then, at either end of the run, I could sandwich an S curve (for expansion/contraction) between two horizontal pieces of plywood, to eliminate any dips there. It sounds pretty simple.