I used RadiantDirect - my 9 year-old daughter and I were able to put our system in back in 2001. We were able to follow their tubing layout, custom designed for our house. We connected our PEX to the manifold/control panel. I had a plumbing contractor come out and double check the heater connections - we used a Polaris.
I ended up working for them. It was good for me because so much of the manifold/controls came pre-assembled. I didn't have to do any soldering - just some simple PEX compression connections and low voltage wiring for the thermostats.
There are other options out there too. Radiantec is good if you're buying on price. So is PEX supply - but there is a trade-off. I do hear from time to time that their level of support is lacking, but I think they are catering more to experienced plumbers and radiant installers, not so much the DIY crowd.
Ultimately, it will depend on how handy you are and how comfortable you are with the work. If you have the tools and the knowledge - go with
PEX supply or
Radiantec. If you think you'll need some pre-assembly and support throughout the process - take a look at
RadiantDirect - I did.
