Solid Hardwood, Engineered and Laminate Flooring - 2nd story subfloor dried out from furnace underneath

I am in the process of installing wood flooring in our master bedroom and our walk-in closet. The rooms are on the second story, with the closet directly over the room that houses our oil burner (baseboard heat). The closet has always been the warmest room in our house.

The subfloor in the closet is very dry and brittle. I assume that the rising heat has dried the wood out over the years (about 30). I am going to replace the closet subfloor this weekend with a good exterior grade plywood.

How do I properly protect the new subfloor (and flooring that will eventually sit on top of it) from the drying heat of our oil burner? Is there some special insulation specially suited for this?

thanks

Perhaps some type of heat reflecting insulation. I have used a product called Reflectix for miscellaneous insulating jobs. It is basically foil-faced bubblewrap. It is thin but you could layer it and is rated for exposed use.