alternety... you are saying to pressurise with air while pouring... other info I have says to pressurise with water to keep the tubing from floating up before the concrete cures.
As for the open loop system... are you suggesting that you tee off the water supply to a water heater/boiler which the water is circulated thru? For some reason I was thinking that even when the heat is turned off that a properly designed system kept water circulating at all times so that it stayed fresh and was diverted either into the hotwater tank or hot water supply so as to avoid stagnation.... I need to look deeper into that. Thought the mixing valve took care of that.....
While some systems advocate using the water heater as a source for radiant heating, I don't think it is a great idea. In the winter, you might have an extra 1000' of piping to move the water through - you are likely to have some places to stagnate some water. In the summer, you don't want that water hot, so then what. Use a heat exchanger so you have a closed system, and a boiler. Most wh aren't designed for the continuous use you might need in the winter, and if sized properly, you then might not get enough to take a nice shower, either.
I think you'd be better off with a boiler dedicated to the task that you can turn off in the winter.
Air works fine. The pex should not be free floating and will not rise to the surface. It needs to be attached. A little air makes bubbles; water makes damper spots in wet concrete. Use high pressure (50psi or more based on tubing rating). Watch the guage during the pour. The way to spot damage is to see pressure drop. Air is nicely compressable. If the house will not be completed and heated before freezing temps you may make a very long skinny popsickle (that can be agressive to components).
Research it. Sharing potable and heating water is considered a bad idea except for some online stores that sell junk systems.
Mixing valves do something else entirely.
Water heaters have much less burner capacity to heat water than a boiler. You can get a wide range of boiler BTU capacities. Water heaters are much less efficient. DHW can be a major component of your fuel bill.
Nothing makes sense until you know what the heating load of your house will be. It is not completely clear in my mind what you are actually trying to do. Trying to use one water heater for DHW and heating will most likely cause bad results under most any heating loads.
I am not sure what your climate is like there. Keep in mind that radiant slabs are not particularly responsive. There is a great deal of thermal mass there. You will not be happy trying to trun it on because of a cold night and then stop in the morning.
From some of the things you have said I strongly advise a lot more research or getting a pro to help. You might be able to find a reputable radiant heating person who will agree to let you pay for just a design. This can be tricky also; there are lot of prople that do this for a living but still do not understand. DIY of heating systems can be dangerous and create a system that may under perform and it will be too late to design it correctly. It is (wait for it) cast in concrete.
Pex tubing radiant heat
I would like to know who makes the best pex tubing for radiant floor heating.
What size is the best for joist applications. Where is the best place to buy pex? Thank you in advance.
Salvatore. From all of my reading it's just not likely that you will beat Wirsbo and it appears to have been proven in all kinds of applications. There are others and a few variations. In certain parts of the country a two pour method is advised. Here in Alabama the weather and climate are so totally different that the whole concept is not very well developed for this area. The fact that the whole floor slab acts like a heat bank appeals to me as well as the physics of radiant heat. For what I've studied I should be able to circulate it in one water heater and use that in series for the hot water supply. I'm thinking that controllers will shut off hot water and allow cold or warm water to flow thru zones that are not being heated... the other option is a heat exchanger and boiler system. I'm still studying and still have not installed radiant floor heat before... but it is being done here and I'm anxious to learn all I can about it...and start installing for customers.
The a,b,and c, after the word PEX is a reference to the X linking method used by the Mfg.
I heard from several non professionals that Wirsbo is over priced, but good. Thermapex seems comparable but perhaps twenty percent less.
Randyj, thank you for your comments.