We have in floor radiant heat in a concrete slab.  Rough in of the Synergy 3D begins this week.  We are looking ahead to floor coverings. How much loss in  efficiency   will occur if we use different floor coverings?  Most of the house will be tile, but would like to know the pros and cons of different options, from the best to the worst.  

Think of your heated slab as being sandwiched between two insulators - the underslab insulation and the floor coverings you choose to put on top.  The more insulation you put on top, the more heat will be pushed out the bottom of the slab.  So, it is an interplay between what you have on the top and what is on the bottom.  What's two inches of underslab foam worth?  R10?

If someone in your household decides that they really must have big thick rugs with plenty of padding underneath, you might want to increase the underslab insulation to make up for what you are doing on top.

I read somewhere it is recommended that you don't go better than R-4.0 on top of a hydronically heated slab.

Here is a link to a good list of R-values for floor coverings.

R4 is pretty extreme. I would normally not recommend going over R2... but what R is acceptable depends on your water temperature needs, which is dependant on your heat source and heat load as well as the floor R value.

I agree, but if you look at the list of floor coverings, you can see how one could get there pretty fast with just an underpad and some carpet and then you'd be pushing heat out the bottom of the slab and wondering where it went. You'd want to be sure to add an extra layer of underslab foam if you had to go the cushy carpet route.

I'm going to have to have some wood flooring as it is and I cringe whenever the salesmen bring out their foam underpads and start talking about how thick and comfy they are.

I'll note again R4 is extreme: pretty much no one should be installing such carpets over their radiant. we strongly recommend an R2 maximum to all our clients. Sponge rubber pads help a lot.

Sponge rubber pads help a lot.

Help do what?

Help keep the total R value down.

Heat doesn't get "pushed" by insulation on the other side of the slab. Heat flows based on temperture differentials and R-values. Insulation on the top of the slab will cause the heating system to raise the slab temperature to keep heat output (out of the top of the slab) acceptable, and that "increased temperature" of the slab will cause more loss through the bottom (and edges, don't forget the edges) of the slab, but the insulation on the top does not "push" heat out of the bottom.

Jeff

Help keep the total R value down.

Is that because they seem to have holes in them as compared to a foam sheet, or is it because the foam rubber material transmits heat better? The foam rubber pads I've been shown tend to be thicker than the foam sheeting. And what about the jute/natural pads?

Heat doesn't get "pushed" by insulation...

Thanks for the clarification. Sorry to use a confusing description. Net result is more heat has to go to slab to get the same effect in the living space, and that means quite a bit more loss out of the bottom (assuming insulation level stays the same down there, right?)

Rubber is much better at transferring heat than foam is. If you look at the chart you posted, you can see slab/sponge rubber R value is about a third of the fiber/jute options per inch.

Posted By ICFHybrid on 06 Jan 2011 01:59 PM

Help keep the total R value down.

Is that because they seem to have holes in them as compared to a foam sheet, or is it because the foam rubber material transmits heat better? The foam rubber pads I've been shown tend to be thicker than the foam sheeting. And what about the jute/natural pads?

I have 1/4" rubber pads under the carpet in my carpeted areas.  I believe that rubber pads are better transmitters of heat for two reasons:  First, rubber as a solid material is better at transmitting heat than natural or artificial fibers - my R-value table says 1.23R / inch for rubber, while fibrous materials are listed as 2.08R / inch.  Also, we have 1/4" rubber pads which are significantly better than 1/4" fiber pads: the rubber has more give to it and feels like a sturdier product.  So, you can get by with 1/4" rubber (R .31) rather than half inch fiber (R 1.04.)  That's a pretty significant difference, though the choice of carpet is just as important.

Jeff

1/4" rubber pads with a thinner carpet sound like the way to go.

Anyone have any experience with engineered hardwood floors over heated slab? Glue down or floating? Clicklock?

If you are going to install an engineered floor over a radiant heating system, you should do whatever the manufacturer of the engineered floor says. That way, you'll be sure that it will not only work, but that it will be warranteed.

That said, wood species are all different, and even with the flooring manufacturer's okay, there are some species that would be sketchy for a heated floor. I can't remember offhand which ones are not okay (other than Brazillian cherry, I believe) but in general, straighter grain patterns tend to be more stable.

Jeff

There are many different types of engineered floors to choose from and some of the particular choices even have (manufacturer-approved) installation options.

wood species are all different

I was under the general impression that once you got a particular hardwood stuck to an "engineered" substrate, it was going to make it much more suitable over heated floors.

I'm not sure what you are saying about engineered Brazilian Cherry (technically Jatoba). While I'm sure there are some manufacturers who don't allow their product over radiant, I've recently looked at more than a dozen who do. Maybe those are the ones you would want to install as a clicklock or floating floor. Just in case.

We will be totally carpet free, with the exception of a few area rugs. Tile for the most part,  but was curious about laminate flooring and the types of material recommended ( foam, plastic etc.)   that may be required when installing on a concrete slab.

we have a 6000 square foot office with bambo and the radiant heat through out and the gaps in the flooring has not moved in years.  It is pretty durable to the radiant heat.  so far the best i have seen