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You can use a water heater for this application but the efficiency is significantly less than a heating boiler. Of course you have to factor in the higher cost of a boiler in your cost benefit analysis.
You also have to consider the heat loss of the space you want to heat when sizing the water heater or boiler
If only one temp is desired for the entire area then you only need one zone. If different areas require different temps at different time then you can consider zoning but keep in mind that radiant is not a quick recovery system. It takes quite a while to get a space up to temp if you turn down a radiant zone.Aside from tubing you'll need a circulator and a line voltage thermostat (assuming you use a water heater). You should keep your heating loops to 300' or less so you'll probably need manifolds which can be pre-fab (best option) or you can make them up with a bunch of TEE's. You'll need an expansion tank, air eliminator (like a Spirovent), pressure gauge and thermometer or a combination gauge (temp & pressure). Ball valves on either side of the circulator for servicing, a purge station which can be an all in one fitting like this oneor a ball valve and a TEE with a boiler drain in the line above the ball valve. There should be shut offs (ball valves or integral shut offs in a pre-fab manifold) so you can isolate each loop for purging and for isolation capabilities (if you have a leak for example). The water heater should run at ~110 degrees 120 tops. If the water is much hotter your floor will be too hot. If you can monitor this system regularly you can fill it manually otherwise you should use a feed valve like a Watts S1156F which is basically just a pressure reducing valve designed for heating systems.