Hi Speeedr,I have a similar situation at my house.Above my garage is my mother-in-law's room.Your builders idea seems a bit extreme.My builder ran duct into the garage ceiling which helps buffer the cold coming from the garage.Now don't get me wrong,if you can afford it go with his idea.As far as the drain in the garage that would be great but most states do not allow it because of enviromental concerns,such as oil or gas or other pollutants possibly flowing down the drain.

Being that it is a garage, having HVAC in the same area can have deadly results by allowing exhaust from the vehicles into the living areas. Using radiant will prevent that. If the contractor did the slab correctly the water will flow out towards the overhead doors and not pool in the garage, so no drain should be required. A big plus is just think how nice it would be to get into a warm cor and a very cold day.

I am glad to see someone else has the thought of radiant heat in a garge floor. I too am planning to build a garage this summer and I too would like radiant heating, I am a mechanic by trade and plan to work in the garage and don't want to lay on a cold floor or have a hot air furnace blowing on me all the time, I also plan to keep my show car in there during the cold New England winters, is this a wise thing to do, the garage will not be attached to the house. Anyone know of any websites on radiant heating info.?
thanx, Carguy, Beacon Falls Ct.