I'm doing some preliminary heating work on my house running 1/2" pex supply and return lines for future radiant wall panels, and wanted to ask some advice on insulating the lines.  I intend to use closed cell foam to insulate the pipes wherever they pass through an unconditioned space, but what about where they pass through conditioned spaces?  Some of the areas I'm concerned with are when they are routed through closets or between floor joists (joists will most likely be a future staple-up radiant and insulated with dense-packed cellulose).

The heat loss in these spaces is not entirely wasted, but not entirely useful either.  I was just hoping to get some insight from those with more experience on if it is worth the effort to insulate piping where I have anywhere from 2 to 6 1/2" pex lines (both supply and return) running through these spaces.  Would you insulate every pipe separately, or maybe build a channel using something like 1/2" blue board to run all of the pipes in?  I'm sure the answer is "it depends" but for some more information the house is at 8500' in the Rocky Mountains (I believe about 8500 heating degree days).  The house is pretty leaky, and I'm in the process of upgrading the insulation, but there are places that I need to run piping before finishing with the insulation.  The heat source will be an electric boiler and 6 4x8 flat plate solar panels (already on the roof, might as well use them!) so low temperatures are a plus, although the heat load calc (yet to be performed) will determine system temps.

Thanks,

Trevor

"Pipe" insulation has probably caused more frozen pipes than it has prevented (false sense of security). Pipe going through and unconditioned space will likely freeze if you use a setback thermostat, have another source of heat that could satisfy the thermostat controlling the new radiant walls, a big wind comes from the "wrong" direction once in ten years, etc.etc.etc.

The good news is that PEX can freeze without bursting (not so, fittings).

As rule, all hydronic pipe should be inside the thermal envelope.

Unless you have considerable solar storage I would save the panels for a pre-engineered solar domestic hot water heater.

I guess I should have been more clear about the "unconditioned" spaces. The two unconditioned areas will be the attic just above the rafters, with considerable amounts of cellulose on top (probably 12+ inches, plus the closed cell pipe insulation) and through my crawlspace. The crawlspace is uninsulated (the floor is insulated above) now but the walls will be insulated by the time any of theses pipes have water in them, and there is enough heat leakage that my pressure tank and incoming water lines have not frozen in the 40 years since my house was built (saw -12 last winter, crawl space stayed at 50 or so degrees). So freezing pipes is not my concern in these areas.

As for the storage, I'm planning on a 600+ gallon tank. 6 panels is way too much for my domestic hot water usage, but I had them going last winter before a leak developed and I definitely notice higher energy bills (and this winter is noticeably warmer then last) without them. They were plumbed to an 80 gal tank and contributed to both space heat and domestic hot water (long story, open heating system w/ poorly done staple up thanks to previous owner, will be completely replaced this year w/ a proper system).

Sounds like you're on the right track. 1/2" wall will do.