Tuesday, August 26, 2008

Staple Up Radiant Heat

A while back, I posted some pictures of us installing radiant heat tubing between the floor joists and the sub floor. For months, this tubing has been hanging beneath the floor. But now, because its time to put some real ceilings in our house, I've finally started properly securing the tubing to the bottom of the sub floor. From my internet research, it looks like the heat transfer to the floor is twice as good with aluminum plates (40 btu/hr/ft) than without aluminum plates (20 btu/hr/ft). But pre manufactured aluminum transfer plates cost almost $1 a piece. A few thousand plates could equal a few thousand dollars!


Instead of buying plates, we decided to fabricate them ouselves. Lowes sells one hundred 5"x7" pieces of aluminum roof flashing for $15. (Fifteen cents a piece - that's more like it!) We built a jig to speed up the bending process. It is possible to make between 100 and 200 radiant heat transfer plates per hour with this simple jig, which consists of a board with two strips of 5/8" plywood screwed to it. A 5/8" bolt helps form the plates into the wooden channel. Then we use a piece of hardwood flooring to crease the "wings" of the plate. It is possible that the radiant heat plates sold on the internet are made of a thicker gauge aluminum than our DIY aluminum plates, but I think these will function fine. I am slightly concerned that the plates could abrade the pex tubing as it moves due to thermal expansion and contraction, but the edges of these pieces of roof flashing are fairly dull, so it's probably not a big risk.

I first used a manual stapler to attach the plates to the subfloor. Unfotunately, the manual stapler would not reliably drive the staples deep enough into the plywood and my hands were getting sore quickly (waaahhh). My Arrow electric stapler was even less powerful. So I borrowed a narrow gauge pneumatic stapler from my father-in-law. I turned the air pressure down to the lowest setting that would still operate the staple gun (70psi), and I set the depth control on the gun to minimal. Even with these adjustments, the pneumatic stapler would occasionally shoot the staple clear through the aluminum plates. No problem - shoot another staple - they're cheap and quick.

The most tedious aspect of attaching the pex to the subfloor was dodging all of the flooring nails. The subfloor beneath the rooms with parquet and herringbone floors was peppered with thousands of sharp flooring nails sticking out everywhere. Fortunately, the flooring nails (technically they're called cleats) are made of crappy metal that breaks off just inside the plywood if bent back and forth a few times. After a full day of breaking off nails and stapling up aluminum plates, my neck was sore. (waaaaah... more whining).

After attaching over 1000 of these plates to the bottom of the subfloor (and finding a few places where flooring nails had at least nicked the tubing), I wanted to pressure test the pex lines. To perform a pressure test, I bought the requisite pex manifold, fittings, and pressure gauge. Figuring out what to buy is tough if you've never seen the stuff before. I had to go through the whole pressure-test-thing once before when we poured the basement slab with the pex embedded, so this time around it was easier. Back then, to be on the safe side, I bought Wirsbo brand radiant heat components. This time, I bought Mr. Pex brand components because they're less expensive and of similar quality. I've included a picture of most of the goodies, as well as a close up of the inside of one of these manifolds, which might help someone else understand how the zone control valves work.

Pressure test report (subtitled, how to repair punctured pex) to follow in a later blog entry.

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4 Comments:

Blogger Tyson said...

Thomas,
If you have space between the pex tubing and your ceiling material you should think about adding that bubble wrap foil insulation to help reflect your heat upward. This will help your efficiency a whole bunch.

We finally got our Waterfurnace installed and working.

Tyson

September 11, 2008 at 12:45 AM  
Blogger Ralph Doncaster said...

The aluminum has very low emissivity but high conductivity. Therefore the aluminum spreaders are a lowE surface. Without the heat spreaders I'd agree that insulation is a good idea.

January 8, 2009 at 6:33 PM  
Anonymous Anonymous said...

Thanks I almost cancelled my radiant project at home when i calculated the cost of plates but i think this will bring it back to life.

December 12, 2009 at 6:41 PM  
Blogger CarlofET said...

Do you get any noise from expansion/contraction using this system?

January 18, 2010 at 12:34 PM  

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