Radiant Tubing

I am SO looking forward to experiencing radiant heat!  Think about it: warm feet, nearly constant temperatures with low energy input, no filters to change, no noisy and uncomfortable air blowing out of ducts, no worry about whether there is mold growing in your ducts: the advantages are many.  And in a house this size, it is so simple: There is only one run of 250 feet of pipe, so no manifold and network of thermostats.

The  1/2" diameter PEX tubing was pretty easy to install, even though my friend and I were near the bottom of the learning curve.  (This would be a tough task to accomplish solo.) We spent a couple hours learning that the 1 1/2" tapcon screws were having trouble holding in the adobe base layer, which is noticeably softer than concrete.  Solution: 3" course-thread deck screws driven straight down with no pilot hole.  Not one of those has pulled out.  True, we didn't pull the tubing into quite as small a radius as we might have otherwise, but I don't think there will be any downside.

The only place were we doubled on clips up was where the tubes transition from the floor up the wall to the heater/pump assembly.  You can see the blemish in the adobe where one of the tapcons pulled out.

So next step is to bury the tubes in a 1 1/2" layer of adobe.  That thickness makes it easy to use 2x3s laid flat as screed boards.  The entire adobe assembly consists of the base 4" layer, the next layer at 1 1/2", and the 1/2" finish layer for a total of 6".  That's a lot of thermal mass!  So I'll basically set the thermostat once in the fall and leave it untouched until the end of spring at the end of heating season.

Adobe Floor Preparations

There are several layers that need to be installed before I can start with the adobe:

Four inches of pea gravel.  The discoloration is due to the gravel being slightly damp from the previous day's rain.  Note the hand tamper: that was a lot more work than I'd anticipated.  If the space had been bigger, I probably would have considered renting a gas-powered tamper.

The next layer up is the 6 mil polyethylene vapor barrier.  However, before I installed that, I pre-fit the first layer of foam (1-inch thick) and cut holes for the pipe penetrations.  This photo shows how I used the foam as a template to know where to cut the vapor barrier for the pipes.

With the poly in place and stapled up the wall, I taped the vapor barrier around the pipes using Zip Tape.  I don't have a picture, but the corners are folded like Christmas wrapping but on the inside.  Since the goal is to make the poly as air-tight as possible, it's better to avoid cutting: hence the corner folds.

This shows the second layer of 2" foam in place at the other group of pipes.  At R-5 per inch, this provides a total of R-15 under the radiant slab.

Practically done:  The joints have been taped, and spray foam has been added around the pipe penetrations.  The last thing to do is glue the side foam panels down and tape the side joints.  It was only a matter of a couple hours until the first load of adobe mix was flopped down and leveled.  More on that next....