Traveling, eh? hmmm...
Originally Posted by perryT200
Nat, what is the brand of the foam flooring your are describing as 2-3000 psi?
And I can't find any rigid insulation that would be suitable for an in-floor radiant heat install. What were you thinking of using?
I'll share my experience with foam. Perhaps it'll be useful to make an educated guess as to next steps:
Rigid foam comes in several densities. 20psi and 30psi are the common residential ones, though they go much higher (I've seen up to 100psi). A 20psi piece of XPS can support 20 pounds of pressure on one square inch before crushing. 30psi is what you'd lay down before pouring concrete for a garage or the like. 20psi is fine for most other uses. That's what I used below my plywood floor and it holding up perfectly well.
I'm only familiar with the pink 20psi and 30psi XPS Owens Corning stuff, which is called Foamular c-200 and Foamular c-300 respectively. Dow chemicals makes XPS foam insulation as well, but it's blue.
I would have no aversion to using these products in a radiant floor heating system as long as the fluid temperature remained at a safe level below the maximum operating temperature of the XPS foam product. Foamular has a max operating temp of 74°C (165°F).
There are a number of ways you could attempt to make trenches in the foam for laying the aluminum heat spread and pipe. A router comes to mind, but it'd be messy. A utility knife could be used to make the cuts for the edges, then a chisel could pop out the in-between chunks.
Additionally, if I were to do a radiant in-floor heating system in a bus using this technique I would want to go with 3"-4" of foam in the floor. 2" is a common XPS thickness, but after creating the trenches for the pipes there would probably be only 1"-1.5" inches of foam beneath the pipes. That's only around R5-R7.5. It seems like a lot of the heat would be lost into the metal bus floor.