Hydronic In-Floor Heating

[bcboomer]

My Hydronic installation is limping along and I've realized that it would be very easy to run a return line under the 16" x 36" area under the table. This is where we have breakfast every morning and surf the web many evenings. In our last house we had hydronic in-floor heat in key areas, including the eating area, and it really improves the comfort level at lower temperatures and saves lots of energy.
I'm thinking that a single run of 3/4" pex, fastened to the bottom of the 1/2" teak/holly plywood, backed by 1" of armaflex should be adequate. I have no idea how much heat escapes from pex but, if that doesn't work, then I could change that out for 3/4" od copper tubing.

Anyone out there with experience at this?

[Paul L]

Not sure about pex but 5/8 radiator hose is something like 4,000btu pet 100 ft, if that helps.

[kmacdonald]

The thermal conductivity of PEX is 2.86 and copper is 196. The units don't matter in a comparison. Use copper!!!!!!!!

[bcboomer]

So, if pex is similar to heater hose, then about 120 btu for my 3 feet.

Copper is a lot more for sure, but my problem is that I don't know how much heat I need. It may come down to trial and error if I don't find someone with experience. Maybe no way to predict since I don't know what the temperature will be of the return water/antifreeze.

Thanks for the numbers.