Kitchen Remodel and Radiant Heat.

I have a small kitchen 15x 10 that I gutting and redoing from scratch. One wall houses a small hot water radiator. I am planning to remove this radiator. I do not want to lose the heat source though. What I plan to do is route pex under the kitchen floor to make it radiant in this room. I do not plan to pour a cement floor over the PEX cause I can not add any additional height to the floor. I was going to route the pex under the subfloor and across the joists in one continuous loop and tap into the existing radiator connections and insulate below it so the heat can only radiate up. Maybe even add some reflective material to ensure the heat is not lost downward. Basement is all open so I have full access to do this. Does this sound like the best solution for my application. The finished floor will be tile.

A radiant barrier might help, and on the staple up pex, you might want to consider the aluminum panels to spread the heat more. Most radiators and heating systems run at 180-degrees, which is too hot for a floor - the wood nor your feet will like it, so you may need a tempering valve, which would give you grief balancing with the other branches.

Good point. Did not think of that. What I might do is since my basement ceiling is unfinished, I may put in a pex manifold in and run a zone to each radiator on the first floor. This will allow the under mount radiant floor to only circulate if its thermostat calls for it. It will be hot water still but will not run all the time when other zones are calling for heat. Do you think this is sufficient to fix that problem?

No its not... Unless you want to skip across the floor...
Personally in akitchen you might want the option of standing in one place to prep food!

The addition of a tempering valve to lower the water temp (assuming you can't do it at the boiler) would solve that problem, but lower temperatures may not provide the quantity of heat you need. It's all a big tradeoff...small radiator, higher temps, verses lots of pex and lower temperatures with the larger, but cooler, floor as a radiator. Then comes the heat transfer (thus the metal plates to distribute it so the wood, a poor radiator, can compensate).

I have learned the reason for the mixing valve. I saw this great video on thisoldhouse.com

http://www.thisoldhouse.com/toh/video/0,,20052923,00.html

This is exactly what I want to do. I have no problem installing the pex and heat transfer plates. What I would like help on is the mixing station. I would like to purchase a kit maybe. Else I can build it if I knew what components I need. I guess I can go to my local HVAC distributor and they can build me one and I can just plug into it. What do you think?

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What I have on mine is a fairly simple mixing valve. It mixes the cooler return water with whatever amount of hot from the supply it needs to maintain the temp of the main loop.

Right a mixing valve in involved here without a question. But also is a circulating pump and some relays for the thermostat. I am after a diagram I can follow to build this station. Unfortunately I can not find a kit for this so it has to be from scratch I think. If anyone has a diagram or good verbiage that would be a great help.

If you use Onix tube instead of pex, your per foot cost will be a bit higher but you do not need transfer plates. You can run a bit higher temps with onix and it is easier to install. Pex needs transfer plates mainly because it grows like crazy and makes noise, and pulls away from the floor, where Onix is stapled closely and tightly to the floor and has zero movement/ No noise.
The mixing valve will still be needed of course, and a properly balanced system. For help with that, contact Watts Radiant 1-800-276-2419 or go to www.wattsradiant.com
If you call, just ask for hydronic tech support & tell them what you are facing!
They will give you all the info they can based on the info you have, and may direct you to a local hydronic supply for the actual calcs on a balanced system.

An awfull lot of trouble and expense for a smallish kitchen. Why not stick a toe kick heater under a cabinet and be done with it.

Now the toe kick sounds like a good idea. But if you can't get enough radiant surface, how about a hydronic coil and low speed fan.