My heating system is oil hot water, radiators. I'm remodeling a bath, can I take out the radiator and connect the feed and return to pex tubing running under the floor?

Probably not. The operating water temperature for in floor heat is lower than the water temp for a radiator.

I think you mean to just cut the radiator out of the circuit, and connect the two ends together, is that correct? If so, then yes you can. You aren't switching to another loop, just eliminating the radiator. Have I got that right?

Dear Missouri Bound

Your correct, I want to just remove the one radiator and connect the two ends of the floor tubing to the corresponding ends of the radiator feeds.

And I think PEX Alumium is one of the approved tubing types Warmboard uses.

Thanks

Pex designed for your usage will work but I need to remind you once again that the water temperature your system operates at is the main problem. I would hate to see you jump through all the hoops installing the in floor/under floor heat only to have your floor tile pop or having the floor to hot to stand on situation that has happened to many people come to pass on your install. Please read up on the style of heat you are proposing to install to get the acceptable hot water temperature limits then see what temperature your boiler operates at before making your final decission. In most cases you cannot lower the boiler temperature since the rest of the radiation in the home was calculated for the heat the boiler operates at. If you lower the temperature of the boiler so the in floor heat works OK then the rest of the house will be cold. There are water heat exchangers you can use to lower the water temperature without having to turn the boiled down to solve this problem..

Warmboard is good stuff being precut for the tube so the install is easier so that part will not be a problem but the water temperature will. Good luck with your project.

Thanks for the info, I'll look into it.
A thought,
Would the use of a flow restricture valve, similar to what's on a radiator, solve the problem?

No a flow restrictor just restricts flow not temperature. Now it will change the temperature in a room due to the heat loss of the radiation type or style. I only mentioned this since I have seen exactly what you propose to due and it failed due to exactly what I mentioned that the boiler operating temperature was to high. No you could always try it or check around and get different opinions. Just make sure you get your opinions from a professional who has experienced what you are trying to do.