Nome, Alaska or Key West, Florida? Have your heating contractor do the calculations based on where you are and the construction of your house. He's required to do this.

No, you won't need any other heat. Radiant is great heat. Have you thought about how you are going to do air conditioning (if you need air conditioning)? No duct work for heat means that if you want central air you need to build duct work anyways. Ductless minisplits are an option but can be expensive and contractors don't always know what they are doing with this type of AC. Also have you thought about what type of flooring you want to go over the radiant? Not all flooring types work well over it. Tile is good.

thanks for the info. yes we want AC I will look up ductless minisplits never heard of them. we will have tile floors. glad to know we won't need other heating.

We have in floor radiant. Really enjoy the warm floors. I think it is kind of like a spa as opposed to regular heating because you can walk around in socks or bare feet in the winter and enjoy the warm floor sensation. Sometimes laying on the floor feels really nice. The dogs love it also.

Our house did not come with AC (had swamp/evaporative cooler) but I missed having it on the hot days so we added the ductless minisplit which is great for zoning. It also cools the house super fast because the cold air comes out at the ceiling and falls around you. As a result you feel it as soon as you turn it on. The hot air rises so it also seems very efficient. Plus with no duct work you have no dust blowing around and no build up in them to contaminate your air. It is very easy to clean the filter right at the indoor unit.

In the summer at night we only have the master bedroom unit on and that works very well. You have to be careful to place the unit where it doesn't blows on the bed because it will likely be too cold. We used a ceiling cassette and blocked off the vent that goes over the bed. Still plenty cold.

The downside is the cost. Economies of scale are at work for both forced air and central air. With more people buying the equipment it is alot cheaper. Also the installation/repair people are more familiar with those systems.

Edit: Forgot to mention that for almost no extra cost you can get the heating added to the ductless minisplit. We only used this once when we had a valve go out on our radiant floor heat and it was great to have the redundancy. The unit put out super hot air in the middle of a cold winter.