underfloor heating under an existing slab

[hvacj]

hi, I'm searching if there is any possibility installing a underfloor heating system on an existing concret slab with minimum re-structuring requirement. based on the information i got from google, seems tat the underfloor heating system is usually implemented into the structure during construction. it's much appreciated if anyone can give me some hints/reference to install a the system on an existing slab.

 

[gepman]

What is the application, industrial, commercial, residential? Is it for comfort heating or freeze protection? Do you want hydronic or electric?

I have never heard of doing this. Unless it is for some type of industrial freeze protection I think that it would be much more trouble retrofitting an underslab system than it is worth.

I have retrofitted for freeze protection when a building use was changed to a cold storage freezer but we were ripping out the floor anyway. I don't have any experience in residential or commercial underslab heating systems.

 

[GMcD]

You need to search some of the sub-floor systems like Warmboard, Raupanel, and the like - grooved wood panels with heat transfer plates that can be installed on top of the slab. There is one guy I am aware of who has developed a tool to cut grooves in concrete spabs to directly place PEX tubing into the concrete surface, but that's a very specific application, and very labour intensive.

There are also some good electric mat style radiant floor heating systems (Nuheat) that will not take up as much space as a sub-floor system.

The one big issue that you also have to consider is that the existing spab may not be insulated underneath, or around the perimeter, so you will have significant heat losses to the ground, severly comprimising energy efficiency and cost to operate. It may be more efficient and economical to use more conventional wall-fin or panel heaters depending on the occupancy of the space. You could also consider a radiant heating ceiling in the space, if the "warm toes" are not critical for your application.

 

[coffmarm]

Here's another supplier:

http://www.warmtiles.com/aboutwarmtiles.html

 

[Nella95]

Here's another:

Please use for reference only:

http://www.sunqest.com/radiant floor page.htm

This sounds like what you want though.

 

[hvacj]

first of all, thx all of u guys reply.

let me make it clear, I heard tat there is a technology out there, it is like attaching the hydronic tubes underneath an existing concrete slab, and sandwiched by an insulator at the bottom. (concrete - tubes - insulation). the hydronic tubes are apparently "clamped" and attached to the concrete.

i can only find the in-concrete or on-top of concrete floor heating technique, but never see any like wat i mentioned above, so if anyone has idea about tat, it's much mcuh appreciated if i can have a hints on it.

thx

 

[GMcD]

So, let me get this straight- it's an existing slab on grade? Or a suspended concrete slab that you can access the bottom of the slab?

Are you wanting to heat the floor surface of a slab on grade, or the ceiling surface (bottom surface) of a suspended slab?

If it's a slab on grade, how on earth do you expect to dig under the slab and install heating tubing? And then if you do manage that, how do you expect the heat to conduct up through the thickness of concrete to get to the desired floor surface temperature?

Maybe it's so hard to find anything like that because there's no such thing? Or it's just not done due to the laws of physics getting in the way?

 

[Nella95]

When I worked for a radiant floor heating/HVAC company - back in '97 - it wasn't possible to put the fin tubes on an existing slab - that was done in the construction process, however it was possible to retrofit wood or carpet flooring.

 

[hvacj]

actually, the situation is, there is a 2 storey block, we need to install a floor heating system for the 2nd floor. the thing is, some fancy carpet is already installed on the 2nd floor, plus, the client doesn't want to raise the floor height, so there is left with no choice but look at the floor heating underneath the concrete slab.

the concrete is like 150mm thick, we aware it might take couple of hours for heat conduction from the underneath to the surface of the slab. coz this system is most likely to be operated 24/7 during winter n to keep the floor at a constant temp. so the time it takes to warm up the floor surface initially is not a concern.

coz i m very new to this industry, n i did try to google if there is any system like tat out there in the market but yet find any solution. so im just wondering if u guys have deal with any similar design condition like this ever, n could share yr experience...it's much appreciated...thx

 

[GMcD]

I would run away from this project. It has too many restrictions to work, if at all. Carpet = insulator, so to get the carpet surface temperature to where you want it, the concrete floor surface has to be even warmer. Couple that with the 150mm of concrete thickness (try calculating the thermal mass of that chunk of density) and it's a no-win situation. Concrete responds to temperature changes at a rate of around 2 hours per inch, so it would take a minimum of 12 hours+ to get the concrete mass up to temperature from the bottom side, even with ideal contact surfaces from the PEX tube to concrete interface. Unless the room being served is a steady-state condition, IE: no transient loads/changes in room heat loss/gains due to windows or other factors, then you "might" be able to control the room comfort using a constant temperature slab set-up. The conditions you describe would be impossible to allow any kind of room temperature control IF there are any changes in the load during the day.

The closest thing that comes to mind for your fantasy system would be Polytherm - a rigid foam insulation panel with little dimples to press the PEX tube into, and then you might be able to clamp/attach that up to the underside of the concrete, but your contact surfaces from the PEX tube to the concrete slab will be very small, requiring even higher heating water temperatures to get heat to conduct up into the slab over.

My advice: convince the person with the carpet to pull it up and allow a PROPER installation of floor heating instead of some cobbled together bag of problems.

 

[FoMoCoMoFo]

how is the first floor being used ? any heating required ? do you have easy access to the bottom of the concrete ? can it spare ceiling height ? is the exterior insulated ?

 

[gepman]

I agree with GMcD that you should not install a hydronic system below the floor. What happens to the floor below if it springs a leak? The odds of a leak would seem to be fairly high if there is not access to the entire area. It doesn't sound as if it is going to have good performance in the heated area, it won't have good efficiency, the odds of a poor installation are high, and the chance for damage large.