Site Designed by Axis Web Design. Store Cart Checkout Account. Installing Pex Tubing for Concrete Slab Underfloor Heating Installing Pex tubing for concrete slab underfloor heating is one of the easiest ways to install radiant heat. On top of the compacted earth or sand, install a vapor barrier. Extruded or expanded polystyrene is the material of choice. Install the wire mesh or rebar for the concrete slab. Attach the tubing to the wire mesh or rebar using plastic zip ties.
Here's a concrete slab we're getting ready to pour with the radiant heat installed professionally. Notice the styrofoam going up the edge of the slab to reduce heat loss. This is one step I see left out of a lot of radiant installations.
I do think concrete floor heat is a great way to go. If I were building a new home I would install it in all my concrete floors. If you're thinking of installing you're own radiant heat floors, you can buy your pex tubing right from Amazon. This pex tubing is for good for light commercial and residential applications. The simple answer to that is YES , especially if you're re-modeling and installing new tile, carpet or wood flooring. But there are some things you have to take into consideration.
There is and electric radiant floor heat system that can be embedded in a mortar mix or a self-leveling concrete overlay. Then you can install tile, carpet, or wood flooring over this to have heated floors. Floor height may be an issue for older exiting homes.
You would have to remove the existing flooring and allow for this new floor. The thickness of the new floor would be the total of the concrete overlay and the type of flooring you choose. This could be approximately 1 inch more or less. Go from concrete floor heating to concrete floors. Home page.
A concrete overlay is a very thin layer of specially designed bag mix concrete used to resurface, repair or stamp existing concrete surfaces. I'll show you how to use self leveling concrete to repair, resurface and level and old concrete floor. This is a step by step guide that'll teach you how to!
Radiant heat tubing in a concrete slab needs to be closer to the top of the slab than its bottom, normally in the top 2-inches of concrete. Placing tubing deeper in the slab means, simply-put, that more heat will transfer into the slab and ultimately into the soil below than will be transferred up to the top of the slab and into the occupied space. Our photos above and below show that the radiant heat system tubing for this improperly-installed system was placed right on top of the styrofoam insulation intended to be at the bottom of the concrete floor slab.
This placed the tubing at varying depths but generally about 7-inches below the finished floor surface, with tubing at some locations near the slab perimeter placed inches deep in the slab!
Re-bar was laid atop the tubing and also at the bottom of the slab. It should have been roughly mid-slab. After reviewing photographs taken during installation of the radiant heat floor slab described above, here's what we wrote to the owner and to the contractor:.
I am doubtful that we can successfully and economically heat the cabin with radiant in floor heating as the current system is designed and installed, and it is unfortunately the case that the cost-to-cure is prohibitive as the slab would need to be completely replaced with one using proper insulation and tubing placement. That's when we began digging into the installation details of this project. The floor slab and radiant heat tubing had been placed by the contractor while we were unable to attend the jobsite.
When the heating bills were excessive and when the heat, running hours a day for weeks, was unable to raise the interior temperatures above 60 deg. The most economical fall back is to install electric baseboard heating or possibly hydronic heating using the existing electric boiler which was installed to pump heated water through the radiant tubing in the concrete floor.
Meanwhile we shut down this unfortunate radiant slab heat system, installed a few portable electric heaters, and given the tight, well-insulated construction, we found we can keep the little cabin comfortable for a fraction of the cost of heating the earth underneath our floor with the contractor's heating installation. In , observing water leaking up through the slab in this location from below, the floor was opened to permit further investigation. Our photo above shows accumulating groundwater just below the slab insulation.
A system to drain off water and prevent water entry of frost damage to the slab was needed. Our photos above and below wer made possible by breaking into the floor slab with a jackhammer, removing concrete to expose the exact details of how and where the radiant heat tubing was installed in this floor - shown below.
Following this exposure of the tubing and convinced that the radiant heat system could never work properly we removed the boiler intended for use in providing radiant heat and filled in the damaged areas of the floor with new concrete and tile. We agreed that the description of the failure of this installation needed some clarification, and added the following information that should be considered:.
Keep in mind that this was a small new structure sq. So the insulation, air tightness, materials, heating details were known. The building was super insulated, tiny, airtight, with double-glazing throughout, leading to an expected low heating cost.
If the owner's actual heating bills for the structure had been even five times what was promised for this building that was occupied only part-time, the owners would have been happy.
They were more. In fact, the utility cost to heat this tiny cabin resulted in bills that more than doubled the corresponding costs of the nearby 's vintage two story large old, comparatively poorly-insulated house on the same property, exposed to the same conditions. And the exploding heating costs were observed when heating the building well before the coldest part of the heating season.
The effects of putting the tubing deep into the slab created a problem of heat transfer losses to the ground, not just a matter of longer response time to warm the building. Even if money had been no object, the system simply could not heat the building to an acceptable temperature.
The problem with very deep radiant-heat tubing, combined with incomplete insulation, is that even with just 12 to 18" of concrete above the tubing, heat flowed enough into the ground below the building that. And this was in a new, small, airtight one-story well-insulated building. If we have enough thickness of concrete above the tubing Where 1" to 2" tubing depth is the best design and 6" is considered a lot, in this building we are looking at 18" or more at least in many areas, maybe 24".
With radiant tubing at those depths, the concrete begins to offer not just a lag time in heating Mr. Darling's point but also an actual resistance to heat transfer until we begin losing at least some heat into the ground. The contractor and others tried to improve the system's performance by changing the boiler settings from those set by the manufacturer on its integrated circuit control board, upping the circulator size and capacity, checking flow rate through the system, checking the thermostat controls.
Our photo left shows where we found the radiant heat floor tubing when we later broke open a section of the floor slab. Radiant tubing was at the bottom of the slab, in this area more than seven inches down in the concrete, and set atop the foam sub-slab insulation. Our photo above on this page shows that tubing was in some sections more than 18" deep, and adjacent to a large area where sub-slab insulation was simply omitted by the contractor. We also measured floor temperatures in different areas of the building, mapping clearly where the radiant heat tubing dropped to the bottom of the footing-portion of the monolithic-slab footings!
That deep run, probably combined with the incomplete insulation at the level drop between slab bottom and the integrated footings, were almost certainly the prime cause of the failure of this system to heat the building.
As our reference document s below show by calculation and model, ultimately, the heat flow into the ground for tubing really too deep in the slab can be significant, even if there is insulation below all or part of the slab.
In the structure described here, not only was some tubing 12 to 18" or even more below the slab top, the insulation below the slab was incomplete, inviting ready heat flow into surrounding soils. Despite varying opinion by some radiant floor installers, consumers, and installers as well should be wary of ignoring the advice of the radiant heating design experts and heat transfer engineers about tubing depth in radiant floor slabs shown just below.
Worse than too-deep radiant floor heating tubing, in this case, because the contractor put NO insulation at the area of soil where he stepped the slab down to the depth of the monolithic integrated footings, we have heat transfer from some of the tubing through concrete right into the cold soil, not just through concrete up into the room through the ceramic tile floor.
In this egregious error, even worse than putting radiant heat tubing too deep in the slab, insulation was simply omitted where the floating-slab monolithic footings were poured.
The R-value of concrete is roughly. The builder located sections of the radiant tubing so that there was about 6" or less of concrete in the 12" footing section" between the tubing and the cold soil, giving us a heat transmission path tubing to soil of R 0. This is a likely area of heat loss at all four sides of the building: where the slab dropped down to form footings.
As an aside the ceramic tile on the finished floor slab was set in mastic - leaving some air spaces and mastic that is a poor conductor compared with tile set in concrete optimal - but we doubt that's nearly as important in the system failure in this case. Our photo left illustrates a successful radiant heat system installation in Minneapolis, MN - a climate similar to that where we had trouble with the Two Harbors system above.
We have better insulation but much deeper placement. QUOTING except for [bracketed comments] "These results indicate that tube depth does have a nontrivial effect on the thermal performance of a heated floor slab. There is a performance penalty associated with leaving the tubing at the bottom of the slab vs.
The analysis performed was also based on steady state conditions. It doesn't predict the consequences of the longer response times associated with deeper tubing. These could be significant in situations where a building is recovering from a setback condition, or when heat flow from the slab needs to be reduced quickly to accommodate internal heat gains.
Considering the tradeoffs, perhaps it is time we pay more attention to quality control procedures to ensure that performance is not compromised as concrete is poured over radiant tubing circuits. When future archeologists dig up the ruins of our buildings several centuries from now, will they ponder why we put the heating tubing at the bottom of the slab?
Might they wonder if we didn't know any better? Would they conclude that some builders of the time were just too lazy to bother lifting the tubing? Thinking back to how ancient Romans used lead piping for water supplies, perhaps those archeologists will conclude that even after centuries of experience, we still had a hard time doing this pipe thing right.
We estimate maybe degrees water temperature would be needed at 4" down and well over deg heating water would be needed in tubing 6" down. In the slab in our construction project, the critical tubing, leaving the heating boiler, was placed more than 12" deep in poured concrete. Heating energy costs will increase consistent with the increase in heating water operating temperature requirements. John Siegenthaler, is a professional engineer specializing in radiant heat designs and heat transfer theory in buildings.
Siegenthaler principal of Appropriate Design, a consulting engineering firm specializing in hydronic heating design. This formula is not as intimidating as it may seem. C, Ste. One thing we have found that if the soil conditions are quite damp, there definitely needs to have some type of insulation under the slab. Another theory I have read is that the heat as it goes down, which it will, some is that it radiates horizontally, which makes insulating the edge quite well. Wendell, there is not actually any contradiction between the Montana DOE research you cite above and radiant heat floor slab insulation requirements.
The DOE photo below left shows a typical Montana construction practice that gives a thermal break between a concrete floor slab not yet poured and the exterior foundation wall.
I've read quite a lot of supporting research on slab and slab perimeter insulation for radiant heat flooring, and I have some direct experience with installing radiant heat and more with inspecting radiant heat flooring problems. Quoting from the conclusions of the Montana DOE-sponsored study you cite, [2] [photo at left showing interior foundation insulation before the slab is poured, U.
DOE, op cit. The energy savings vary slightly depending on the insulation configuration and building type. Although the current installation practice in Montana does not extend the interior footing insulation to the top of the slab, based on empirical data, this study concludes that irrespective of the insulation installation configuration, Montana buildings will save energy by insulating the slab edge with R insulation to a depth of 4 ft.
The payback period could vary from 4 years for small retail commercial buildings to 12 years in small office buildings. The study data includes comparison with fully-insulated slabs too, but most important for our discussion, it does not address radiant-in-floor-slab heating designs that, without full insulation, can find an easier heat flow into the ground than into the building - not what we want to see nor pay for in heating bills.
The local practice of insulating the slab footing on the interior allows heat loss along the slab perimeter and thus does not achieve the full savings that could be achieved with full edge insulation configurations, but the savings are still significant. The risk in misinterpreting the Montana study conclusions above would be to apply them generally to radiant heat floor designs and that to improperly infer that complete under-radiant-heat-floor-slab insulation is not needed in cold climates.
That study makes a general conclusion for all Montana buildings and by no means does the conclusion adequately address radiant in-slab heating system designs. The fallacious concept held by the contractor in our horror story was that "once you heat up the earth below your building it will start "giving back" heat to the building and you'll be just fine. His theory was nonsense, as both expert advice and actual field experience proved.
The earth in a cold climate like Montana or Minnesota, is for practical and design purposes, an infinite heat sink. A radiant floor slab heating system will, if improperly designed, keep pumping heat into the ground as long as the heat is turned on.
We saw this in astronomical heating bills and a cold building interior in the Minnesota home discussed above. Heat always flows, and continues to flow from a warmer material into a cooler material.
Heated the soil beneath a building where insulation was incomplete, inadequate, or omitted, will never reach some magic perimeter after which it stops sending heat into the surrounding soil any more than an ice cube placed into the sea will stop melting because it's "cooled down" the water around itself. As the principal author of this material I relied largely on the concrete industry and the radiant flooring industry's radiant floor slab design specifications and advice [1] as they, above all, have a huge vested interest in their installations being successful.
There is no doubt that in virtually every radiant-heat-floor-slab design we need continuous insulation under the slab and at slab perimeter, though the appropriate insulation amount might vary depending on the local climate. The folks who seem to disagree have been people like the bully contractor who himself admitted he had never read instructions, attended a class, nor asked for expert advice. As is often the case with small contractors in remote areas and without expertise, he was "winging it".
Don't try mentioning "thermodynamics" or "heat flow theory" to a bully. Just how bad an uninsulated, under-insulated, or incompletely insulated floor slab will perform with radiant in-slab floor heating depends on some additional variables: climate, soil moisture read thermal conductivity as you suggest , and critically, the depth of tubing in the slab.
In ALL cases we want the insulation in place. But in the horrible installation we describe in these articles, the contractor not only provided incomplete and no perimeter slab insulation, he also buried the tubing so deep in the concrete that heat moved much more down into the cold earth than upwards into the occupied space.
There was so much heat loss that we could not get the room temperature up even in cold but not bitter cold weather, and even though the same contractor had done a great job insulating the upper portions of the structure's roof and walls. That's why we had to abandon the whole radiant floor installation. If the floor slab had been very well insulated, the installation still would not have performed well because of the excessive tubing depth in the slab over 12" down in some sections.
I appreciate the Montana reference and have added it to this article below at references [2]. We are in the steel building business so we have a lot of in floor heat done. They place the foam down and put the PEX directly to this and then place 4 to 6" of sand on top before pouring the floor. I ask why and was told if the have any floor problems they can remove any thing need to. They done this on I think four bldg's. Wendell it's a fair question, and I welcome the disccussion.
But I suspect this may be a case of intelligent people who think things up on their own, make up an explanation that sounds reasonable, but may not know the whole story. The deeper you put radiant heating tubing in the slab the worse the heating system will perform in delivering heat to the interior. Furthermore, the thermal conductivity of sand is much below that of tubing directly in contact with the concrete slab itself. The expert sources I found on this want tubing in the concrete and very close to the slab top surface, an inch or two at most down is best.
I agree that if there is enough insulation under the slab and it's well done and complete, in the design foam, tubing, sand, concrete you describe you will eventually probably warm the slab upper surface, but consider that there are heat flow rates through insulation too, it's not "heat proof".
With 6" of sand and say nominally 6" of concrete, your tubing is 12" down - way too deep, and furthermore, the first 6" of material sand between the tubing and the occupied space, does not quite the same level of thermal conductivity as tubing in contact with solid concrete. The sources I cite at references below point out that there is heat flow resistance through concrete and sand as well.
So while it may not be intuitively obvious, and while it's true that the thermal conductivity of concrete and even sand which is not as good as concrete is greater than insulation, if we have enough sand or concrete above the tubing, and little-enough insulation below the tubing, heat flow down through the insulation can still be significant. Think of it as " heat flow resistance " through various materials. You can have a more conductive material above the tubing, but if you have a lot of it, the total heat flow resistance can still be significant.
Finally, the supposition that "if they have floor problems they can remove anything they need to" sounds highly suspect to me - it's not thought out. In any case you'd have to chop entirely through the floor slab to get to the tubing below, and meanwhile you are paying in higher heating bills than necessary over the life of the building.
We would never have found which sections of insulation were omitted if we haven't had the photos. Similarly his second and fatal radiant heat installation mistake was putting the tubing at the bottom of the slab.
We couldn't see those details without destructive chopping up of the concrete or finding photos taken during construction. My point is that drilling one inspection hole in a radiant heated floor to examine the insulation scheme and tubing depth, even if you could avoid cutting tubing, wouldn't assure you that there wasn't a problem elsewhre under the floor.
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