What type of flooring are you using over a concrete deck 1-1/2" thick with radiant heat in it.  I would like to install some wood flooring over the deck installed on sleepers.  I am very concerned about the stability of the wood in this type of application.  What has been done to stabilize the wood ie;conditioning, sealing,air gap or other.

I have solid cherry over my radiant floors i installed sleepers before i poured the slurry so i had something to nail the hardwood too You cant float a real wood floor In your case an engineered wood floor would make more sense as it can be a floating floor . Your real issue is that you designed the radiant floor temps too accomadate hardwood on top the conditioning of the wood starts with proper water temps with your design

If you have the time it is a good idea to sticker the wood in the building area where it will be installed and let it acclimate to the space for month, other options are moisture reading, the supplier can provide that. low temp delivered water will be best for a wood floor. (100-110 deg.)
Dan

double check with the manufacturer of the flooring you are interested in installing, and ask for their recommendations.

In general, hardwood floors are not recommended to be laid on top of under floor heating systems. This is because wooden floors must be glued down the subfloor and the temperature shifts caused by the under floor heating will cause the floors to shrink and expand, damaging the floor planks. The best option to use in combination with underfloor heating is laminate flooring. I am sure you will find a wood effect laminate floor for your interior. In case you need any more details, check out this source of laminate and wood floors, which also offers great information on how to install and care for your selected floor: http://www.kaboodle.com/store/flooring2floors.co.uk

The idea that wood floors will shrink, crack, warp and buckle when introduced to radiant heating (though widely accepted) is generally a myth. Over 20 years ago I installed 3/8" barrier PEX under 3/4" T&G planking supporting 5" T&G pine driven by 180F from below. The floor is still and now nearly one hundred years old and perfect.

Laminate is thinner and more stable lending itself better to lower temperature design saving fuel, but don't rule out those old floors!

I second Morgan's post. Wood floors are routinely used over radiant without problems.

Radiant heating under wood (or carpet) will be comfortable, but I wonder how much it will effect using radiant heat for whole house heating, especially with the lower/more efficient loop temperatures used with geothermal.

wood and carpet are not the same.

carpet is hard to keep under geothermal optimal temps of 110 or lower. But not always impossible.

Wood is not usually too hard to keep under that temp range. But it's not always easy.

See how different they are? ;)

Agreed, but if one limits loop temperature to 100F, can you fully heat a house with either one?   I should just do the math on the heat flow.  Maybe  R=0 for just using the (stained) concrete, R=.7 for hardwood and R=2.5 for carpet.