We have been working for months with Full Spectrum Solar, to plan the heating system for our house, and Monday it started coming together.
Underhill House will be heated by three mechanisms:
- Passive solar
- a wood burning stove
- infloor radiant heat from solar panels with propane backup.
The PEX tubing for the infloor heat was laid out today in the lower level. The name PEX comes from the term polyethylene, cross-linked. Cross-links are bonds that link one polymerchain to another. This high-tech plastic is put through several processes to make it more durable in the face of repeated heating and cooling cycles, and it does not corrode, which means it can give the much more classic, but costly, copper tubing a run for its money.
The development of PEX tubing made infloor heating attractive. When you combine PEX with improved insulation, and sophisticated controls, radiant heat and solar heating systems become an ideal choice to keep your toes toasty within a small carbon footprint.
The downside is that this stuff degrades quickly in sunlight, but as we are burying it in concrete, it should be pretty safe. How long will PEX last in concrete? I’ve seen figures ranging from 50 to 200 years. The 200 years figure is a wild guess, but so far it has been in use since the 1970s, and it’s holding up well.
Andy DeRocher, our project engineer at Full Spectrum, has prepared a meticulously thought-through plan for laying our PEX. And it’s beautiful too. When I saw the plan above, I wanted to frame it and put it on the wall.
Before he and Mark O’Neal (co-owner and master plumber at Full Spectrum) could install the PEX, they went over the floor plan once more with our construction manager Bryan Dalstrom, who drew out exactly where all of the basement walls and doorways will be. Then Mark sketched the exact map for the PEX.
Mark and Andy guided tubes of PEX along the sketched lines, and Andy fixed the tubing to the Styrofoam with a giant specially made staple gun.
By design, no tubing will run under wall locations. This ensures that no wall anchors penetrate the tubing during interior wall framing. As a result, the tubing was snaked from “room” to “room” through the doorways, tracing out the pathway that we will walk through Underhill House time and again once we take occupancy.
Doug noticed a blank spot in the floor plan and asked why there were no PEX tubing there. Andy pointed out that is the spot where our chest freezer will sit. It would be counterproductive to heat the floor under the freezer. (Nice, Andy. Very nice! – It’s that kind of attention to detail that makes us feel like we are getting the perfect solar infloor heating plan.) All the tubes are now connected to a manifold against the mechanical room wall, where controls for the system will be added at a later point in the construction.
The last step of the day was to temporarily seal off and pressurize the system to check for any leaks. A pressure gauge was installed to hold the system at 30 psi, but much to Andy and Mark’s surprise, nothing registered on the gauge when the line was pressurized. Doug had just arrived after teaching all day, and and it must have been doubly troubling for Mark and Andy to wonder what the problem was with the home owners looking on. To think there could be a leak in this spaghetti bowl of tubing Yikes! But after several minutes of checking every possibility, it turned out that the pressure gauge itself was malfunctioning. Andy and Mark both agreed (to their chagrin) they had never had that happen before but after a fresh gauge confirmed everything was pressurizing properly, today’s job was done.
The system will stay pressurized until the concrete pour is complete to ensure that no inadvertent puncture occurs during the process. It would not be a fun surprise to find that a line got pinched or cut after the concrete has cured!
Tomorrow this entire work of art will be covered in 4 inches of concrete. It’s kind of like Buddhist Butter Sculpture. Now you see it – now you don’t.
But what is going to look like a Clark Kent concrete slab will actually be a Superman high performance radiant floor that will maintain comfortable temperatures in the rooms above it with minimal use of fossil fuels.