Not so much of an inspection question as advice. I am thinking of trying some pex tubing under my kitchen floor, running it temporarily from my electric water heater, I realize that it’s a code violation but it is temporary for a trial run. The room is about 15 x 15 ft, floor is about 2-1/2 " thick and the timbers are 10 " + in diameter about 3’ apart. I have been told to run the tubing about 8" apart which would get about 4 runs per joist space. If this works I will be adding a water heater with a closed system and do the rest of the house. I have access to 300’ of tubing from a friend who installed an outdoor furnace and should be able to find a circulating pump easy enough. I will add a thermostat if it seems to work ok. Keep in mind this place was built in 1872 I can try this for about $350 for pump and tubing. Any tips, suggestions would be a help.
Thanks,
http://shop.pexheat.com/site/index.htm
http://shop.pexheat.com/site/download/ph_RadiantPEXManual.pdf
Your softwood floor at 2.5" has about R3+ insulation value so install at least R12 insulation under the pipes/floor system. Don’t get tricked into using some foil-faced bubble plastic as outrageous claims are made about its R value which is usually only about R2-3 in the end!!
Make sure the space above the insulation is airtight as infiltrating cold air from the outside through the joist system will steal heat.
Consider installing the pipe in a conduction fin system to better and more quickly distribute the heat in the water to the floor.
Charles,
Most of the heat will get lost in the wood.
I put mine in concrete and it takes 8 hours to warm the floor. But then the concrete stays warm for about 24 hours.
I have mine on a thermostat and it works fine.
if you put carpet on the floor this too will stop the heat transfer.
The heat will not get “lost” in the wood. Heat is lost when it gets to the outdoors or ground from the heated structure.
The first few hours of heating will be to “charge " or bring the wood up from 65-72 deg to the operating temp for radiant floor heat of about 80-82 deg. This will not take near as long as heating up 5-8” of concrete since (1) the specific heat of wood is much lower than concrete and (2) there is much less mass of wood to heat
Very true, however the concrete will hold the heat much longer than wood…
because a lot more heat (btu’s) got stored in the large mass of concrete. Actually, in the same conditions, heat will be released from the concrete at a much faster rate than from the wood since the R value of concrete is lower than wood, therefore faster heat transfer.
this has turned into a argument about heat loss, the question is about instalation. run your tubing as designed make sure to use reflective metal brackets to hold the tubing in-place ,then insulate the under side. sure you will looae some heat at what cost is questionable, anything you can do to augment your heat supply is fun to try . if you get caught up in the engineering lose ratio and the other obsticules you would not try any new sources. have fun with your project.
Make sure you leave the pipe clamps loose enough to allow the pipe to move as the expansion and contraction of the pipe occurs.
Mr. Douglass:
I think the items in red were already covered in my post #3…plus a little more advice
*“Your softwood floor at 2.5” has about R3+ insulation value so install at least R12 insulation under the pipes/floor system. **Don’t get tricked into using some foil-faced bubble plastic **as outrageous claims are made about its R value which is usually only about R2-3 in the end!!
Make sure the space above the insulation is airtight as infiltrating cold air from the outside through the joist system will steal heat.
Consider installing the pipe in a conduction fin system to better and more quickly distribute the heat in the water to the floor."*
**
BTW, the pipe installation fins/brackets are conductive, not reflective!
I believe the linked installation manual covers it quite nicely. 
Whatever happened to putting on slippers? Hell of a lot easier that all this mess you guys are comming up with…what’s wrong with you people?
Alabama vs Ontario, Canada…
If you need slippers, they need electric blankets on their feet…:mrgreen::mrgreen:
Yes it does Brian!! Thanks for the link!