I would be very careful with "electric" radiant heat outdoors. The products I am aware of are for indoor use ONLY. Out door products must have different ratings/quality control and have to be able to handle huge swings of temperature, moisture and humidity. These are swings that are never dealt with in an indoor area (if they do, there is a big problem with the indoor space).

Heated streets (like Moscow's Red Square Square) utilize hot water pipes to keep the snow and slush from building up on the roads/side walks. That is a serious amount of engineering. Infra red might be your best bet.

We have considered the infrared heaters but with the height of the ceiling our contractor thinks it will be ineffective. The room is only 400 square foot but the ceilings are vaulted quite high. Also to note, we will have a small outdoor gas fireplace in the corner with a blower as well.

Use electric radiant heaters with white elements so you will not be seeing red light when the heaters are on. We have specified radiant heaters for many years with great success. Consider using Infratech or Fostoria that have damp location listings. Here is our Ideabook on radiant heaters http://www.houzz.com/ideabooks/20390530/thumbs/Exterior-Electric-Heaters

I lived in a home in Vail for 8 years with in floor heat and loved it! We also melted snow outside using the same system. It would take forever to gain enough heat for increased comfort for humans outside with heat radiating from the floor, IMO.

Hope this helps! ClearLED.biz

A follow-up thought on running expenses: prepare the foundation for your floor well to minimise heat transfer DOWN, you want it going up. It can be quite expensive to heat the cement that is chilled from below for the sake of warming tiles that release a bit of heat upward. A barrier to ensure you maximise your result is important.

It would be difficult to have an effective heating system outside on the floor whether it is hydronics or electric resistance. An idea however is to use a higher wattage electric system embedded in a seating area like concrete benches etc to provide sitting comfort. That would be effective. you just need so many btu's to heat the outside that is why the outdoor heaters are so effective because they product high btu's and heat shields that reflect the heat towards occupants, much more than any hydronic or electric system can produce out there because heating the air is important. These embedded concrete heating systems used for snow melting can be designed to heat benches and other structures outside to contribute to the comfort out there.