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radiant heat - need aluminum diffusers?

I plan on installing a radiant system in the spring in a new residential construction. I would like to install pex above the sub floor. I've seen pros and cons about if the aluminum diffusers are really needed or not. At about $1 per foot X 2700 square foot house (+ basement and garage heating) that adds up to a lot for something that many people have differing opinions on. I see two options if using aluminum plates. 1. Buy the preformed plates and install into a 1 1/8" sub floor routed with the grooves for pex. OR 2. Have a 1/2" sub floor then a sheet of aluminum, then another 3/4" plywood again routed for pex. Of course there is the option of not using aluminum at all. Any thoughts on this? If I can save $3000 on this, I'd like to, but don't want to risk the effeciency of the system long-term. :confused:

Re: radiant heat - need aluminum diffusers?


I have radiant in-floor hot water heat throughout my current home and will put it in my next home which I hopefully will build next spring as well. There is nothing like in-floor radiant heat. I would never go back to forced air.

I have heat in my concrete basement floor, as well as through my main floor and second floor. As I built the house myself I turned on the zones in stages so I could see the difference between what I used and didn't use.

Stone/concrete is the best it pulls the heat away from the hot-water lines and retains the heat for much longer. There is light weight mastics (for better terms) that you can pour over the hot-water lines. The con is putting flooring ontop of that matic.

When I did my current home I installed one floor with the aluminum fins and turned on that floor. It worked great. Then the next floor I initially didn't put the aluminum on, but found the heat not distributed as well. So GO WITH THE ALUMINUM!

You can save money however. I found it less expensive to go under the subfloor then get the special routed subfloor(s). The alumimum fins then also act as your attachment to the bottom of the subfloor.

I found keeping in mind of the type of finished flooring you install helps as well. Like I said stone is the best... any tile really works well. Wood is fantastic, the harder (or more dense) holds heat too! However when buying carpet get radiant rated carpet pad... it is worth the money because it holds heat instead of blocks it (and it is much more cushy than plain carpet pad).

Hope that helps.


Re: radiant heat - need aluminum diffusers?

Dayna, thanks a lot for responding! I appreciate your thoughts. I did a proof of concept in my existing home as well (116 years old, under floor, with carpet (inc. the radiant rated pad) in a bedroom and hallway and tile in a bathroom. I honestly do have some "hot-spots" and thought that the under the subfloor heating was not very efficient (need higher water temp). Your post is starting to make me question that thought. In my POC, I used the aluminum foil bubble wrap stuff in between joists. Do you really think that going under the subfloor is better (in terms of efficency and cost) than having the tubes part of the floor. I really wouldn't mind doing the routing myself. I've talked to several of those panel manufacturers and came to the conclusion that I could make something similar for far less cost. Thanks, Dom

Re: radiant heat - need aluminum diffusers?

My husband and I are putting water to water radiant heat into an 1820 stone house and we too debated the diffuser plates. After installing 1/2 of the heat we have decided that it was a wise choice to add the plates. It spread the heat more evenly as it heats the plates. We will be adding yellow pine flooring on the top of the heat.

We checked into purchasing pre-cut end panels also. We found them very expensive so we purchased 19/32 OSB and cut them into 6 1/2" strips and devised a template for the router to make the turn on the end. The 6 1/2" strips with the metal transfer plates made our pex 8" apart which was about the minimum pex could be bent easily. The pex stayed into the groove easily. We found it was easier to glue and nail the strips down first before routing. Just do not nail where you are going to route.

Re: radiant heat - need aluminum diffusers?

Thanks for your post. I had not thought about making the strips. That's a much better use of the material that trying to route the whole thing. Thanks a lot. :)

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