I use 1/2 " pex under the floor to heat my house. I stapled it directly to the underside of the subfloor using aluminum radiator plates to hold the tubing in place and supply the necessary surface for radiation. reflective foil under the tubing and lots of insulation complete the installation. You need to run the boiler at higher temperatures to compensate for the insulating value of the flooring and subfloor. Good luck!

Almost every contractor I know who does thermal floors uses Pecs. It goes down quick and easy. and they have an incredible product line specifically for this. Don't forget to put in your reflectors. I'd go with the 1/2 to 3/4 inch. You really aren't after a lot of flow. A gradual transfer of heat is better. Also if your floor will support it. I've seen some that were concreted over. The concrete acts like a heat sink. It absorbs the heat and releases it over time. thermal delay is something like one hour per inch of concrete. It creates a "set it and forget it" way of dealing with the thermostat. If you have someone in your house that is constantly fiddling with it or don"t have enough structure then adding concrete may not be for you. I just thought I'd throw it out there for you.

Underfloor heating has several big "Cons", the "pros" do not out weigh them for me as we have a long fall with warm and cool days here in Germany. This CANNOT be handled by most underfloor heating as the heating/cooling times are often of an order of 2 days.....or more.

If you still go for it, may I suggest that you add another another form of heating to handle those times of the year when the weather is undecided in temperature, say a pellets stove or even a few rads on seperate circuits that you can control easily......

There is nothing worse than in spring or fall as having to have all the windows open just to get the temperature down to a liveable level!!!! Seen it, but NOT got the T-Shirt!!

Also, plan carefully for the possible leaks that can happen with ANY hot water heating system. Make sure you know about them REALLY quickly and that you can repair them quickly too.....

If you have a balcony, the circuit that runs inside the house near to the balcony can be quickly affected by frost being brought into the house by the balcony strengthening, I have seen several hoses get a frozen circuit because of this. One took almost till spring (2 months that year) to unfreeze.......and then it leaked....one concrete floor to break open!!!

All in all, I cannot personally recommend underfloor heating for anyone.......sorry.

I have to disagree with Andy Germany. A properly designed and even more important installed system will work just fine. Controls, zoning and mixing valves are a must. I have seen too many poorly designed and or installed systems, that has led to unmitigated hell for the home owner. I am surprised at your experience's as in floor heating originated in Europe. I was in the Netherlands last year and visiting family. I too was roasting in their home. The central plant that serviced their area ran year round for domestic hot water as well as heating. I looked at their controls and was surprised at the lack of control they actually had! Not to mention it looked like it had been installed by a three legged Gerbil. Again back to design and installation. There are lots of excellent products out there with good technical support.

Even with a perfectly installed system, you still have the problems I mentioned that it takes too long to react to relative sudden changes in outside temperature, mainly in the time in the fall when the evenings and nights are cool, but many days are still warm, or in the spring when the same can happen.

THAT is the big CON of underfloor central heating.

If you haven't lived through it, you may not understand it.

Thats why you definitely need another form of heating with a quicker reaction time, as I also mentioned previously....

Of course if you live where a sudden change from summer to winter and back again happens (could be possible!), then of course you only have to wait the 2-4 days warming up and the cooling down again in spring......

Sadly, in Europe it simply does not happen like that......we often have 1 - 2 months of mixed temperatures both in Autumn and Spring. That is one third of the year.....that is a long time to freeze and boil!!!!

I agree that it is very comfortable in deep winter, but there is also a train of thought that blames underfloor heating for extra colds as man has got used to fires warming his front and leaving his feet and back cold for around 1 million years.....but underfloor heating is relatively new and the human form has not got fully adjusted yet......!!! Nothing proved as far as I can tell from the web.

Also tiles, carpets and other floor coverings have to be specially made to function correctly with underfloor heating, or serious deficiencies may become apparent if the heat cannot escape readily from the floor.

For people with allergies, underfloor heating tends to swirl tiny particles that would normally just lie on the floor and get picked up by the Vacuum cleaner, around in the air and cause problems.....they also tend to stay in suspension and do not end up in the vacuum cleaner quite so quickly.....forced air has the same types of problems in that area I am lead to believe.....

One should think long and hard before deciding on such a heating system......

8 x 8 beams with a 30 foot span 4 ft oc look suspect. Better visit your local city plan dept. or a structural engineer before adding all that water weight.

FYI, make sure that, if you are going to install this system, you obtain 'ThermaPEX' rather than 'AquaPEX', as it is rated for 210-deg liquid as opposed to 180-deg for 'AquaPEX', and I think it is white rather than red or blue. If you search for a supplier, they will have all of the requisite fittings, valves, insulation, mounting hardware, etc. that you will need.

Also, if you have any idea about installing a thermal mass, the product to use is 'Gypcrete', not concrete. It is about 2/3 the density of concrete and is designed for this use. Also, if you intend to use it, the better method of installation is to mount the tubing above the floor and encase it in Gypcrete. That is assuming that you have had an appropriate structural evaluation of your floor system.

If you install this system, you will have to tinker with the thermostat timing since there is a delay in the process relative to when you will 'feel' the room warming and the same is true of the continuing warming after the thermostat is satisfied. That is the part that many homeowners have difficulty with and complaint about.