Concrete, Radiant Heat and Carpet Pad

[gradwell]

Not necessarily a boiler room topic, but related.

I was curious as to what everybody was using on their concrete radiant floors in carpeted areas for padding. My concern is that not
all padding will release the heat. Any suggestions would be appreciated.

 

[BrownianHeatingTech]

There are pads designed to allow heat transfer for radiant uses. I would suggest asking around locally, to see which products are available (I presume you don't want to mail-order something like that). Any decent flooring place should be able to tell you which products have the lowest R-value.

Joe

 

[gradwell]

The problem I had asking locally, is that I received several different answers.

Felt was a common answer; however, I know there wont be much give to this product and being that it is a concrete slab I has hoping for a little forgiveness. Also, felt is not very moisture tolerant, tends to be dusty and depending on the material it is made from, can be an issue for allergy sufferers.

Another suggested a Urethane product which I know will be softer but must have a very high R-value.

Third was a typical rebond product which will offer a little softer feel, moisture resistance and though a higher R-value than felt, still only around 1.7 R-value.

Seemed to me that the rebond may be the best option as it seems to address the primary concerns which were heat transperancy, moisture resistance and comfort. I just wanted to know if all of you were using a similar product or an alternative. Also, if a total combined carpet and pad R-value of 3.8 was acceptable over top of the concrete radiant floor.

I know this may seem like a dumb question, but this is a new construction project and after all of the money spent on the Econoburn and install, I don't want to do anything to restrict the heat. Thanks again to all!

 

[Piker]

I do not recommend the installation of flooring that has over 2.3 R-value to any of my customers. This is a number that I picked up from a manufacturer of radiant floor systems, (nor sure which one) and it's the standard that the other heating contractors I know use. I am sure this number depends on other factors, ie the insulating value below the pex, heat load of the room, transfer rate of the radiant system to the surrounding subfloor, etc... but it's probably a pretty safe number.

There are alot more carpet and flooring manufacturers who are sensitive to the needs of radiant floor customers than there used to be. 10 years ago if you asked a carpet company what the R value of their carpet was, they would tell you that carpet goes on the floor not in the walls.

I am sure there will be different thoughts and ideas on this topic.

Cheers

 

[BrownianHeatingTech]

Approximately R-2 to R-2.5 sounds like a good bet for a maximum value, in my mind, as well.

You can certainly make radiant work with a higher R-value, but you will start to push water temperatures that reduce or eliminate many of the benefits of radiant.

A note of caution: the concrete itself has an R-value, and certain "lightweight" mixes may have much higher R-values. You didn't specify if this was a slab on-grade, or a pour over a wood floor. In the latter case, contractors often specify a lighter mixture of concrete (or a substitute like gypcrete), for structural reasons. If they do not use the correct mixture, the R-value of the slab, itself, can cause issues.

Joe

 

[gradwell]

It is slab on grade.

Unfortunatly, the carpet my wife has selected alone has an R-value of 2.1. Couple that with the the 1.7 R-value of the pad and you can see I well exceed all of your recomendations. Fortunatly however, the only carpeted areas in the home are bedrooms. An area that I dont mind having a little cooler.

I would have problems explaining to the wife that she couldnt use the carpet she wanted as she was not a big fan of me experimenting with wood heat and the money associated with it. So I think I had better keep my mouth shut and hope for the best.

By the way, I am about 90% installed which has been a task, but getting close.

The next big adventure will be feeling confident enough to light it! Ha ha!

Thanks for the advice!