I really don't know much about this topic so I'm hoping for some direction.  I've read about solar thermal/solar hot water systems & understand the basics, but have some questions..

Would it be possible to install a system like this but rather than use it for hot water, use it for radiant heat in a basement slab?  We are currently looking at options for heating our basement once we finish it.  Adding a basement zone to the system is running about $3000, so if we eliminated that we'd have some money to play with.  My thought, whether legit or not, was that if we installed the tubing in the slab now, when we do finish the basement we could add the solar portion.  I know that upfront costs would be more than just adding a zone, but heating that slab for free all winter should definitely reduce the heat load for the rest of the house. 

Here's my biggest question - in the summer, is it possible to turn it off or redirect it, maybe to heat water instead?  I don't want to add to the cooling load in the summer.

Am I all wet on this or could it work?

Hi Jerk,

We've done a handful of basement slabs which seem to be working out well.  I don't have a lock on how this is done but I'm learning.  There is a bunch of stuff here but it's my opinion that I wouldn't use 1/2 pex.  Solar is all about flow and you only have about 6 or 7 hrs to cram it in so let pie help you out.  If you are not going to put the system in right away make sure that you run a feed and return line to the attic and some bell wire for a sensor.  The answer is yes you can use the system in the summer and you can preheat the water in the winter.  Because this is low temperature distribution it is even more efficient than heating hot water.  Hope that helps!

Flathead

Check out builditsolar.com

He built both a solar thermal and solar hot water system. You may be able to adapt his designs to fit your situation.

It will probably never be cheaper than now to install the radiant tubing in the slab. A long term solution might be to install a dual coil indirect hot water heater to supply both heat and hot water to your entire house. You would have the safety of a fuel based system for cloudy days and the night time hours while having an efficient means of sinking as much heat as possible using an evacuated tube solar heating attached to one of the heat exchange coils in the aforementioned hot water tank. I am in the process of doing something similar because the high cost of electricity in New York negates the potential economic benefits of a geothermal system.

We assume that you are pouring an insulated slab????? If you don't insulate the slab from the earth, you are, mostly heating the dirt.
If you forget this step, and already have a poured slab you may be able to place rigid insulation on the slab, including a radiant barrier, then tubing, subfloor and finished floor.

I saw a study a few months ago that told that most users are disappointed with radiant floors because the floor never gives off heat like other sources. It also noted that most ended up using more energy because the users turned up some other source of heat to get that warm blast. It was noted that the radiant systems did a better, less costly job of heating a space but it's all in the user's perception. The only specific are that had no or fewer complaints were bathrooms, where users now step barefoot on what used to be freezing cold tile.

This is definitely possible- it's a matter of setting up the different heat exchangers/buffers/pumps to control it the way you want it.

Embedding length of PEX in the slab for pre-heating the water prior to any hot water heating system works pretty well too.

R10 would be the absolute minimum sub-slab insulation to use. If you went with 4" of EPS instead of 2" XPS you'd get R16 for about the same money as R10 of XPS. XPS is mechanically stronger, but that's not a huge advantage under a slab.