I would like to put in a radiant floor in a kitchen heated from below the floor with water tubes between the joists.. The normal water furnace radiator in the kitchen is in a bad spot and should be disabled and the same line would be connected to the plastic radiant heater lines with diffusers. the flooring is 1 inch thick planks which I would level with 1/4 inch finishing plywood. Then possibly glue on the vinyl flooring. My question is what is the maximum temperature the plastic can take and would the thermal cycling temperature change damage the flooring. Is this a recommended method or how would it be done. 1 inch flooring with the metal groove diffusers wont cause much of a temp gradient

you need to ck with the maker of the plastic pipe to find out there temp rating, infloor heating is installed under vinyl floors
the trick is to use the heat defusers, and insulate under the pipes
staple that infloor piping tight to the underside of the floor

i cant tell you what your system temp should be
you havent giving enough information