Heated floor. In the concrete or laid on top between the strapping?

[Steven Green]

I'm about to pour the floor for my new shop addition. My question is woud it be worth my time to embed pex in the floor or since I'm going to put oak down on strapping for the finish floor would I be ahead to just lay the pipe in the bays between the strapping? The new addition is 1000 sq ft and the old addition is the same. I'ts got radiant in the floor that runs in the concrete. I like the way it heats the floor and the shop so I thought I'd ask our brain trust.

[Dan Hintz]

I'm no expert in the field, but I imagine you'd want it buried in the concrete so it can act as a heat mass... it will take a while longer to heat up initially, but once heated it will be an even heat and stay that way for a while.

[Mike Cutler]

Given a choice of those two systems. I'd go with slab heating, and put the flooring down on top of Elastilon instead of the strapping to get rid of the dead air space.

[james glenn]

+1
I'm no expert in the field, but I imagine you'd want it buried in the concrete so it can act as a heat mass... it will take a while longer to heat up initially, but once heated it will be an even heat and stay that way for a while.

Also you will want to insulate under the slab so as not to waste energy by heating the ground. And, look up how the wood will react with the radiant floor. Oak is generally good, but some woods
do not work well with it.

[Fred Belknap]

I suggest talking to someone with experience putting tubing in concrete. I have done lots of concrete and I'm sure that it takes some special skill or system to get the tubing in the wet concrete correctly.

[jared herbert]

i have a friend that lives in northern mn, just built a house and has the water pipes in a slab with engineered wood flooring laid over it. It works real good and always feels warm. the flooring looks good after 5 years. he is a firm beliver in that system. Also have another friend who has it and the flooring is wide pine boards cut from old warehouse timbers. the flooring has cracked in several places due to expansion, contraction. the choice of flooring is importent.jared

[Michael N Taylor]

You need the tubes in the concrete but be sure you insulate under the concrete with a styrofoam product usually the blue color.

[Thomas Bank]

With the wood flooring on strapping above the concrete - creating an airspace, you're not going to get the thermal transfer so it won't be as effective as direct contact. Also, engineered wood performs better in such applications than solid hardwood. In my designs, I tend to prefer having a radiant floor slab with some form of masonry topping - something like exposed stained concrete, tile, etc. A floating engineered wood floor would be my next preference.

[Jerome Stanek]

Either way you want to insulate under the slab.

[Dave Wagner]

Yes, put the PEX directly in the concrete flooring, you may have to insulate around the slab too, for expansion and contraction and below the slab to retain the heat. A lot of good resources online for this. Make sure you calculate how much tubing you may need (size, flow, btu requirements), since you have such a large mass to heat.

[Joe Vincent 63]

I have the pex in the concrete setup. To heat it we use a small wall mounted boiler. VERY nice. I keep the thermostat on 63 and it is wonderful in the shop. Its actually warmer than in the house, where the temp is set at 72, but it uses forced air. Occasionally the wife will come outside in her bare feel as the concrete feels like a large warm stone.

The earlier posts are correct that you want insulation under the tubing. We used the pink styrex that is designed to support the heavy loads.

Best money I spent in our remodel about 5 years ago - absolutely no regrets!


Joe

[Scott T Smith]

I too have pex embedded in my concrete slab, and love the comfort inside the shop.

In addition to having insulation underneath the slab, you should insulate between the exterior portion of the slab and the ground outside the building, so as to minimize heat loss.

Regarding tubing placement, my slab is 6" thick and I ran my tubing underneath the 6 guage wire mesh that sits on slab bolsters. I did this so that I knew that I had at least 3-1/2" of space above the tubing for drilling holes for anchor bolts, etc.

Pex tubing WILL float up if unsecured during concrete placement, so be sure to loosly attach it with plastic cable ties or something prior to your pour.

[Ray Newman]

My former residence had radiant heat installed when built. As others said, make sure the slab is insulated. If it was me, I would install more than necessary as energy costs are not going to decrease.

While living in that house, we had a oak flooring installed throughout the house, execept in the bathrooms, which had tile. The 3" or 4" wide oak flooring was laid over a mastic specifically designed for radiant heat and was quite comfortable. However, the stone tile floors in the bathrooms were always warmer as the tile was a better conductor and the heat did not need to penetrate the wood.

[Craig Wahl]

I'm just hopefully finishing up my DIY radiant house project. It has definately been a learning experience to say the least. Like Tom mentions, I suspect the air space is going to create an inefficiency in your system. I doubt that it would be a fatal design issue, but when I was researching radiant stuff it looked like suspended radiant systems (which you would basically have here) are the most likely type to be problematic, or at least require higher water temps. I think it is always recomended that you have as much direct contact between the pex and your heating surface as possible- which is not how a suspended system is designed. I would recomend either not using a wood surface, or at least eliminating the strapping and maybe using engineered flooring over pex in concrete. If you are set on using real hardwood I would consider using product like warmboard to eliminate the cavity you would have using strapping. Then you would not utilize pex in the concrete, it would only be ran in the warmboard channels.

That being said, if you go the warmboard route, I would also spend the $300 or so and put pex in the concrete as well so if you or a later owner decided to get rid of the wood floor radiant would still be available in the concrete. In either case I would definately say you have to insulate the slab.