I’m not sure if this is the right forum, but……….. I have an off grid solar house at 9000 ft. I’m only there in summer but (at altitude); it gets cold at night, so I’ve been thinking about a little under floor solar heating. Basics: I know there has to be a heat source e.g. solar water heat panels on the roof, a pump or pumps for moving the water around, probably some kind of thermostat, tubes or mats for the hot water under the floor and, maybe some kind of holding tank between the heat source and the under floor tubes etc. What I need to understand is the automatic parts of all this. How do the pumps know when to move the water (Some kind of trigger in the thermostat……..solenoid) from the heat source to the (if there is one) holding tank? How do they know when, how fast etc. to circulate the water in the floor tubes, when to replace it etc. Does it go back to the heat source for reheating………..or to the tanks, what, etc. I’m looking for some kind of diagram/explanation of how all this works. Any suggestions e.g. websites, links etc.?

If it's warm during the day and cold at night, you would be a good candidate for passive thermal mass. But you can also google for "hydronic solar heating".

The key is to design for a relatively low temp. That starts with selection of tube frequency and size and extends into flooring materials. Look for sellers of radiant tubes and manifolds and you'll find most of what you need in design assisstance.