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.