Radiant Basement Floor

Earth sheltered homes normally get very scaled down heating systems (some even skip them entirely).  Where I live, a heating system is required for occupancy, so rather than get an expensive furnace that I would hardly use, I decided to go with an inexpensive “on demand mini boiler” hot water radiant system.  I got quotes for install that were as high as $60,000, but figured I could do it for a small fraction of that, so I decided to pull my own mechanical permit and do this myself.  I read a couple books and planned it out.  Then I bought the manifolds and supplies from PexUniverse.com (less than 400$ for the basement).

We got it all installed and inspected (our first mechanical inspection) and then had Dysert Concrete handle the actual pour of the floor.

 

Installing the radiant floor was easy, but some of the recordings didn’t work out, so the final video is shorter than usual.  You can read the story below for the details that wouldn’t fit in the narration.

The Video:

The Story:

I started with working out the layout on the computer.  Building code requires that no circuit be longer than 300 ft, and most experts recommend that you balance the lengths of the radiant tubes, so you definitely want to plan it out ahead of time.

I tried a number of different plans that ran the tubes thru the hall to the various rooms, but it was just too inefficient and cumbersome to get things “zoned” well that way.  In the end, I decided to drill some 5/8ths inch holes thru the base of the mechanical room wall to simplify the layout.  With the right tools (DeWalt hammer drill and a long 5/8ths inch bit), that was pretty easy.

We had leveled out the pea stone after the “underground inspection”, but David helped me do some final leveling of the peastone and then Zack helped get the 6 mil plastic down.  This plastic is important for keeping water vapor from the ground out of your concrete floor and is required by building code.  It also helps keep the radon out, etc.

Six MIL?

A mil is not a millimeter.  Six MIL is six thousands of an inch or roughly 0.152mm.  Before most English speaking countries switched from the imperial measurement system to metric, they would have called it a “thou”, based on the Germanic route word for “thousandth”, but for some reason, America decided to go “romantic” language based with this one and called it a “MIL” instead (based on the word for “thousandth” in languages like French or Italian).  This is a similar etymology to how the rest of the world got the word “milli” for the Metric system, hence the similarity.

We don’t use “MIL” much in the USA, except for quantifying thin film thickness.

Since it is difficult to imagine things in thousands of an inch;

• 1 MIL = grocery store bag
• 2 MILS = Garbage Bag
• 3 MILS = Husky Contractor Bag
• 17 MILS = Pond Liner
• 35 MILS = Credit Card

 

JigSaw Puzzle

David tossed us some sheets of insulation and we got started on the jigsaw puzzle.  My rooms are unusually shaped and since they didn’t actually stock those shapes at Home Depot, we cheated by cutting pieces.  We started with measuring, but usually ended up trimming each piece iteratively until it fit.  We taped all the pieces together and shoved trimmings into any gaps along the wall.  Not too hard, but certainly more time consuming than a square room might have been.  This probably wasted about 15$ worth of insulation, so not too bad.

Radiant tube

I marked the radiant tube layout directly o n the insulation based on that balanced plan I had carefully worked out on my computer.  I used piece of scrap wood marked with the right size increments and a can of upside down surveyors paint.  In addition to basic tic marks to follow, I also painted in the end loops so the whole plan would be pretty easy to follow.

Stapling the Pex tubes down was easy and fun, Sherri and I took care of most of it, but the boys were very eager to try it themselves.  I imagine it would have been quite a lot more difficult (and much less fun) without that commercial grade tool we used.  The tool cost quite a bit (~200$) but is very well built and I will use it a lot… I also plan to sell it and recoup most of the money at the end of the project anyway.

 

Connecting the pex to the manifold was straightforward and easy.  There are some simple little brass connector bits and you just tighten a nut to hold it all together.

I got the Manifold, Pex pipe, the Pex stapler, staples and the pressure tester from “PexUniverse.com”.  I had looked at lots of other sites (including sites that put it all together for you, such as Radiantcompany.com), but this one had the best prices and the best hardware.  There are also easy to find “coupon codes”.

John (my brother-in-law) and Zack helped me finish off the third loop.

My sister Bonnie was in town and mostly helped me with the ICFs (another post/video), but she made it into this video by helping me to fill the tubes with water so they wouldn’t float in the concrete. I had been trying to pour it from the bucket into the funnel, but she had the idea to siphon it from the bucket, which was much easier and didn’t get us as wet.

Then we pressurized the system (according to building code) so we would know if anyone punctured the pipe before the concrete set.

Concrete

Concrete day arrived and the guys started with putting down some six by six wire reinforcement.  This was left over from the garage floor and will help prevent cracks from growing.  It also helps protect the pipe and keep it all down under the concrete.

The concrete was pumped in from overhead (renting the pump truck cost ¼ of the job, but was well worth it in terms of making things go easier), and spread level.  They came back an hour later and hand troweled it smooth.

Costs

In all, I paid less than 1$/sft for the insulation, radiant tube, manifold and supplies, then 3$ for the concrete work plus an extra ~500$ for the pump truck and ~1100$ worth of concrete…  So, not bad.

 

I hope to get the “quad deck” in soon so we can put another concrete floor over this basement.