I believe it's usually installed by the tile workers. It's a pretty straight forward DIY job as well. Google 'radiant floor heat' and you should find a lot of web sites that will walk you through the installation process. Best wishes on your project.

Our tile guy installed ours.

We used Nu-Heat mats in two bathrooms.

Tip we read here (after ours was installed, bummer!): Install two sensors (hook up one to the thermostat, the other will be there as a back up to use if the first one ever fails).