Has anyone use wedi Building Panel as an underlayment for a hydronic system? Their website notes the following: For warm-water systems, ducts can be cut into the wedi® Building Panel quickly and easily using a router. The water tubes are inserted and the surfaces are covered with alkali resistant mesh tape and thinset before tile is set. The wedi® Building Panel serves as a combined form of heat insulation and a base for installation. 

I am building a 2500 sq above ground two story. I plan to install radiant in the basement slab and have been considering the above ground floors as well. My builder discouraged me from doing that but I do intend to install in the master bath on the second floor. Underjoist with aluminum plates is relatively cheap but it sounds like it is not ideal. Warmboad is a very good but expensive option and I am not crazy about dropping the joist or having a significant ramp for the tile. I have attempted to investigate the Wedi panl option but found nothing on the web other what was noted above from the manufacturers website. I know it is expensive as well but still much cheaper than Warmboard. If you have any experience or opinion I would be interested in learning more about this.

Rick P.

What is ideal?

First, the heat load, then the radiant floor heating options. Each manufacturer publishes a design output for their product. Even though the original application posed here (removing a cast iron radiator for more kitchen cabinets) is one of the more challenging in radiant floor designs (smaller floor area and great heat load by adding glass) a sub-floor system is often the most practical. The only way to know it the heat load.

When investigation a DIY radiant floor, on should look to the professionals for his lead. "New" technology is often finds a home with the uninformed and you don't want to be a pioneer.

Main floors get heavy aluminum panel or gypcrete in the majority of our radiant floor renovation work here in Minneapolis. Warmboard and gypcrete may operate at lower temps than sub-floor panels (not to be confused with the infinitely inferior "staple-up" or "suspended tube" radiant floors), but a aluminum emission panel will produce enough heat for most applications today, be they renovation or new construction. We are now working on a 1952 bungalow with R-5 sidewalls and after the new AC goes in the attic - where it belongs - and new insulation covers all, the original 3/4" oak floor will warm the home perfects with 140°F design water temperature.

I have a true staple-up (tubing stapled directly to the bottom of the floor joist- in one of my own homes and it does work quite well with 180°F and the addition of several European style panel radiators...circa 1991.