I'd like to be able to heat with wood. The 2 options I found are a Caddy EPA wood furnace or a wood gasification boiler like Tarm or EKO. Either one should go with electric backup.
The hydronic heating including the wood gasification boiler is a much more expensive solution, and it is recommended to have also a heat storage tank. When heating with water I am also concerned of maintanance costs related to pumps, valves etc.

John,

Radiant over an existing slab: It works. However, don't waste your or your clients hard earned $ on any of the reflective stuff for something like this. Instead, use a control that monitors the air temp as well as floor temp. Tekmar makes a nearly perfect thermostat for this. Look at the main page of my website. That was an un-conditioned space with windows all around: w/no insulation below and it's the "most comfortible room in the house".

Beno, you can heat with wood, see LINK. It is super efficient and we call it our Green Furnace , it is an outside gasification furnace so all mess, fire danger etc is outside and it is using a renewable resource. We suggest it to go into an efficient hot water tank via a water to water heat exchanger. The hot water tank becomes back up for radiant and domestic if you ever want to go away in the heating season. It is capable of heating homes, business, many outbuildings etc, whatever you want to plumb it up to. I also agree with John, Even tho I sell reflective insulation, that is NOT THE APPLICATION FOR IT. It is however the application for the BARRIER as it is a moisture, thermal and radon protector all in one. SEE LINK for more info.

Hi from cold WI.

Here are a couple of thoughts for your radiant heating plans.  The Slab you have is probably not insulated so think about how to keep the heat going in the right direction.  Heat does not rise...it radiates, convects and conducts.

Radiant barrier., the shiney stuff, won't work well because it usually needs an AIr Space to reflect back the radiant heat.

If you can insulate the slab, then put down a subfloor with "grooves" for the hydronic system if you are going with boilers etc.  I have seen several plywood systems that are built to take the 1/2" Pex tubing for hydronic heating.  Warm Floor??

Otherwise put down some vapor barrier, then insulation, then subfloor, then Electric radiant heating cables or mats and then tile or wood.  Hopefully you have the height necessary. I just put down a NuHeat 9'x9'  942 watt electric "mat" under a tile floor and love the heat! I could have strung the cables and saved some cash, but I ran out of time for Christmas.

The Launstein Flooring Company in MI has a web site on radiant heating under wooden floors and how best to plan for hydronic or electric.

There is another alternative:
Ceiling mounted electric radiant heating panels.
Low amperage and fast response time these panels don't take up any floor space and nothing special has to be done to make them heat the room or house.
These are the high tech long wave infrared heating panels that use very little electricity.  The 700 watt  2x6' panels will usually heat a 8x10 room.
Solid State Heating Inc in CT makes them.  My cabin in TN has nothing but ceiling mounted radiant panels for heating.  4 minutes from cold to comfortable.

AL

A thermostat will not make a radiant heating sytem operate any more efficiently. If the heat bleeds away it doesn't matter what you measure & control. In the end it is your comfort level which will decide how much heat the system will be asked to put out. The leakage is a function of insulation & how hot & long long the system runs. A Programmable T/s can help if the system has low mass & heats quickly. If you use the room infrequently I think the radiant panels maybe the way to go in a retrofit but will the floor feel warm ?

RE: Ceiling mounted radiant panels.

I have used the radiant panels in several houses and found them to be very comfortable and energy efficient.  The key here is the FEELING of comfortable temperature. 

The floors will get warm ..eventually..but it is not necessary to get the FEELING of being warm.  Example : If you go outside in 25 degree weather and stand in the sunshine..no wind chill.. you FEEL comfortable, IF a cloud comes over blocking the sun's "Radiant" heat , you FEEL cold.  Even though the air temperature never changed one degree.

Floors are great to heat hydronically, but take up a lot of BTU's to heat the tubing, then the subfloor, then the floor .  The lag time can be a long time too. So I used the ceiling panels to get heat in 4 minutes and FEEL comfortable at a LOWER air temp.  I also used electric mat heat under tiles to get an extra boost of heat.

There is a scale of how much you save on energy for each degree you turn down the air temp.  Something like 4% savings per 1 degree of air temp drop.  Why heat the air to 72 degrees when you FEEL comfortable under radiant heat at 65 Degrees...or less?  You know where the hot air goes..so don't heat air..heat people..and floors.

I read the book by the guy who wrote the book on Radiant Heating and Cooling..Richard Watson and Kirby Chapman ( LINK)

Be warm

Al

Al, read your post, am not an expert in radiant heating but must point out one  misunderstanding you have.  Reflective foil can be radiant barriers , but not all radiant barriers are REFLECTIVE FOIL INSULATION!    I agree with you, even tho I sell the shiney stuff, it needs an air space to reflect back !  The Barrier I was talking about is the BARRIER under concrete insulation.  .  LINK

well, I'm glad to see you're changing your tune, but to correct you one more time, yes, radiant barriers are by necessity "shiny". they must reflect, or they are not "radiant" barriers... at least, not any more than any other opaque object is.

"The Barrier" is not a radiant barrier; which is good, because radiant barriers don't work well under slabs. It is plain old EPS insulation, in a roll form which makes it easier to install. Old-fashioned R-value. Not as much as I would normally like to see under a slab, but certainly better than the shiny stuff.

Radiant barrier
From Wikipedia, the free encyclopedia
Radiant barriers or reflective barriers work by reducing heat transfer by thermal radiation. All materials give off, or emit, energy by thermal radiation as a result of their temperature. The amount of energy emitted depends on the surface temperature and a property called the emissivity (also called the "emittance"). The emissivity is a number between zero (0) and one (1) at a given wavelength. The higher the emissivity, the greater the emitted radiation at that wavelength.
A related material property is the reflectivity (also called the "reflectance"). This is a measure of how much energy is reflected by a material at a given wavelength. The reflectivity is also a number between 0 and 1 (or a percentage between 0 and 100%). At a given wavelength the emissivity and reflectivity values sum to 1.
Radiant barrier materials must have low emissivity (usually 0.1 or less) at the wavelengths at which they are expected to function. For typical building materials, the wavelengths are in the mid- and long- infrared spectrum, in the range of 3 - 15 microns.
Radiant barriers may or may not exhibit high visual reflectivity. This is because while reflectivity and emissivity must sum to unity at a given wavelength, reflectivity at one set of wavelengths (visible) and emissivity at a different set of wavelengths (thermal) do not necessarily sum to unity. Thus, it is possible to create visibly dark colored surfaces with low thermal emissivity.
Radiant barriers must face an open air space to perform properly.

Thermal barrier is for slabs, shiney radiant barrier is for places with air space.

I will stand corrected on the shiny comment! I've never seen a non-shiny true radiant barrier. any examples out there?