ECO BROOKLYN INC. » pex

Why do we use aluminium for radiant floor heating?

Gennaro Brooks-Church — Sun, 17 May 2009 16:11:23 +0000

If you have ever wondered why we use aluminium for fins in radiant floor heating here is a simple visual example:

This image is actually to show the benefits of fiberglass over other materials for windows (it conducts very little heat). But the image also shows that aluminium conducts three times more than metal.

Thus the usefulness of it in conducting heat from the pex tubes. It is also light, which is good in old brownstones with rickety old joists.

Adding a Concrete Sub Floor Heat Collector

Gennaro Brooks-Church — Thu, 29 Jan 2009 16:42:40 +0000

I’ve put pex tubes between joists under the subfloor. that is how my
radiant guy designed it. The whole theory that as long as you contain
the heat it will get to the room eventually etc, etc. I also couldn’t
put them above the floor due to a low ceiling.

Since then I have realized the virtue of using things to pull the heat
out of the tubes. Concrete is good and cheap. We all like heated
concrete slabs, right Then you have aluminum fins. Good, but
costly.

So this week I’m going to experiment I’m going to pile a mixture of
sand and small amounts of cement/water onto a strip of plywood and
then press and screw the plywood up against the pex tubes and
subfloor. The concrete will squeeze around the tubes and create a mini
concrete slab! The floor is strong enough to hold it.

The idea is that the concrete will pull out the heat. It is a dense
mass so it will take longer to heat up (and cool down). I don’t need
the instant heat gratification that aluminum fins would give because
the house is hyper insulated and will change temperature very slowly.
If outside temperature changes it will take at least a day for the
inside temp to adjust and that is plenty of time for the concrete slab
to catch up.

We’ll see if it works!

Sound Proofing and Heat Transfer Subfloor

Gennaro Brooks-Church — Wed, 21 Jan 2009 00:20:21 +0000

We have a floor with a high ceiling which means we can lay the pex tubing on top of the subfloor instead of hanging the tubing beneath. The pex tubing takes up valuable space and you can only lay it on top of the subfloor if you have the ceiling height.

Having the tubing on top is better because the heat does not have to pass through the sub floor.

We laid stringers of wood 16 inches on center over the sub floor. They were about one inch high.

We put a look of pex tubing between the stringers.

Then we covered the tubing with a mix of sand and structolite. This dense mass was added around the tubes for two reasons.

One it creates a good sound barrier between the two floors. And two it pulls the heat out of the tubes and into the room.

Structolite is a mix of plaster and perlite. Perlite makes it very light which is important since it is a wood joist floor. Perlite is also a good heat insulator, which is bad since we want the mass to pull as much heat out as possible. So we mixed it with sand which is a good conductor but heavier. It was basically a balance we had to find between weight and conductivity.

We dry packed the mixture, meaning we used barely any water at all and packed it in manually instead of pouring it. Wood flooring is going over it so we didn’t want a wet mix that would take a long time to dry.

The end result is a nice warm floor that stops sound between the two apartments. Price was also a consideration. Sand and structolite are very cheap yet very effective in their uses here. The labour was a consideration since it took time to pack the mix in. But it still was much cheaper than any other combination that I can think of.

One important point is that we did not put any tubes or mass near the walls. Instead we put insulation. This is to keep the heat inside the house and create a dense insulation barrier between the heat and the cold. This keeps the house warmer and with a lower heating cost since less heat is lost to the outside.