We are installing radiant floor heating with pex tubes. We had a set of challenges:
The floor height was low or the floor already had wood flooring on top of it.
In both these cases it did not work to put pex tubing OVER the subfloor. So we had to hang it below the sub floor. This is not ideal since the heat from the tubes has farther and more to travel through in order to get to the room above. To make up for that you need hotter water temperatures and this costs more money.
The standard way of dealing with under floor pex it to attach aluminum fins to them. This draws out the heat nicely.
I had issues with that route.
1. we had to snake the pex through existing joists so straight aluminum would fit so well with our windy pex.
2. fins are expensive.
3. aluminum has high embodied energy.
So since Eco Brooklyn is all about innovative green technology we decided to challenge industry standards and we set out to find a cheaper, more labor intensive, less embodied energy approach. For me these three elements are key to green building.
Cheap is easy to relate to. Everyone likes cheap provided the quality isn’t. Embodied energy most people can get. It basically means less impact on the environment.
More labor intensive is something people don’t get. But for me it is very important. I have people coming to my doorstep basically begging for work with sad stories of families to feed. Why would I not find a way to employ them? The best way to do this is to reduce my materials cost so I can afford to increase my labor cost.
This means buying cheaper raw materials and assembling them on site with labor.
Doing this is the most powerful way of keeping the money in the community.
So I figured I wanted something that pulled the heat out of the tubes. Cement is cheap (but labor intensive). And it is gotten locally. Pex tubes in a concrete slab work great for example.
Of course attaching cement to the bottom of a floor is not easy. There were considerations:
humidity issues of wet cement
weight issues of dry cement
keeping it attached for over 50 years
We tried many things:
Plywood cement sandwiches that we screwed up
Metal lath like a stucco job
Particle board with holes in it
It took a couple days to find a solution.
What we settled on is foam insulation for pipes that are filled with cement and then screwed up to the subfloor around the pex. At first we punctured the foam with holes to let the humidity out but then we found the screw holes were sufficient. NY isn’t humid in the winter. We also started out by wiring it up but found that screwing it was better and more long term since the cement will dry around the screws.
We used external screws that won’t corrode.
The foam had the right amount of rigidity and flexibility. It was naturally rounded to hold the cement. And it had the added benefit of insulating the cement from below. The heat only has one way to go once it is pulled out of the pex: UP. And that is where we want it.
Here is what the final thing looks like:
First we cut the tube and splice it so it lays more flat:
Then we put cement into it:
Then we screw it up around the pex tubing:
Here are some ways we deemed not good because they either didn’t stick to the subfloor or took too long:
Wire lath with cement:
Using wire to hold it up had issues with longevity:
The end result is that we think we found a good solution. Factoring in costs and labor the price of a radiant floor cement installation is cheaper. The work is not complicated and can be done by an unskilled person. It takes about twice or three times as long as installing aluminum.
For small jobs where you are making a green brownstone I think it is a good alternative to aluminum fins. And again, it might make sense for large jobs too if you have time and want to save on materials.
Of course the big question is whether it will work. We have yet to set up the heating manifolds. But I’m pretty sure they will work just as well as aluminum fins and definitely better than nothing at all. I don’t see any issues coming up either.