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Radiant heat in a floor (C) Carson Dunlop AssociatesRadiant Heat Floor Design & Installation Manuals
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Radiant heating system design or installation manuals: free PDF downloads.

Page top sketch of an electric radiant heat floor installation layout is provided courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company.

This article series explains how to avoid some fatal mistakes when installing radiant heat in a concrete floor slab by describing an incompetent radiant heat floor installation along with an explanation of why things went wrong and how to avoid these errors.

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Radiant Heat Slab Installation Manuals, Research, Products, Guides

Photo of workers installing a radiant heated slab is courtesy of InspectApedia reader Connie.

[Click to enlarge any image]

Pex tubing supports to get PEX tubing to the proper heighnt in a concrete slab radiant heat floor system - cited & discussed at InspectApedia.com

 


Reader Q&A

On 2022-07-04 by InspectApedia-911 (mod) - properly-constructed concrete slab can carry considerable weight

@Zack,

Fair question but as you put it, not possible to answer. A normal, properly-constructed concrete slab can carry considerable weight but "heavy machines" is undefined. For sure there are industrial installations where an engineered slab to carry much greater weight could be required.

On 2022-07-02 by Zack

In a commercial building with heavy machines and 6” slab with radiant heat, would insulating under it compromise the concrete .

On 2021-11-23 by Inspectapedia Com Moderator - an accurate radiant heat floor design is important

@warren gilmore,
The radiant heat floor design that would be right for your house should be informed by an on-site meeting expert I don't know something about how the home is constructed including his insulation, windows, sun exposure, heat loss rate at cetera.

Generally people want the garage heat to be on a separate Zone and therefore a separate loop from other radiant heat sections and in the living area is generally the installer may run the tubing closer together in areas where a cold floor would be least welcome such as in a bathroom.

You mentioned vapor barrier but of critical importance are the quantity and workmanship of insulation installed below your slab. If that's not done correctly you could end up with a system as bad as the one we described on this page.

On 2021-11-22 by warren gilmore

I am pouring a slab floor garage and living space one floor 50ftx 60 ft. 30ft garage 30ft living space what would you do for the garage area for radiant heat and for the living space? would you use the same patern for both spaces? and be 2" from the top of finnish slab.and what kinda of vaper bearier would you use for the ground? cover under the radiant heat tubing?.this home is in western washington the N.w.. Thank you

On 2021-11-01 by inspectapedia.com.moderator

@Roger Shields,

Certainly there are some small radiant heat system boiler is made entirely of stainless steel. But I'm not sure that would solve the oxygen problem.

On 2021-11-01 by Roger Shields

Is it possible to obtain pumps, boilers and other fittings and equipment that do not contain iron so non oxygen barrier pex can be used? Are non iron equipment more expensive

On 2021-07-11 by inspectapedia.com.moderator - where should radiant tubing be laid

@Anonymous,

We don't know the construction, dimensions, layout of your home - details one would need to make a technically-confident reply to your question,
but in general bathrooms are places where people most like a warm floor as that's where we're barefoot and standing on tile, not warmer wood or other surfaces.

Depending on the layout of your bathroom, I'd at least like to have radiant heat under the walking-on part of the floor and might omit it under a vanity and certainly not close to the sides of a toilet;

so if it were my bath I'd include radiant heat the wider most-walked-on area of the floor.

On 2021-07-10 by Anonymous

I'm putting in slab hydronic radiant floor in new construction basement. My contractor did not run tubing in my bathroom saying that there's enough tubing in the rest of the flooring that the bathroom floor will only be about 1 degree less than the rest of the flooring. Should I have him run the tube in the bathroom?

On 2020-12-29 - by (mod) - radiant heat boiler on-time in cold weather

When weather is colder, John, you would expect to see the boiler on for a longer interval;

Affecting the boiler cycle rate are a number of factors; to decide if it's behaving normally we ought to review those:

- outdoor temperature
- age and type of building - some idea of rate of heat loss
- presence of mixing valves and manifolds that recycle radiant heat floor water and keep it from reaching a too-high temperature
- setting of temperature for the floor loops
- settings on the boiler's aquastat itself: HI LO DIFF
- presence or absence of a domestic hot water tankless coil on the boiler
- boiler fuel: oil/gas
- temperatures seen on the boiler gauge (and pressure)

Generally a longer "ON" cycle is more-efficient; it takes about 5 minutes for a boiler to get up to full operating temperature.

On 2020-12-29 by John H - is it better to run the boiler for longer intervals?

Thank you very much for the swift reply! I'm sorry but I'm utterly ignorant in this area so for clarification I have to ask - is it acceptable to have the boiler cycle on/off every 12 minutes or so as it currently does or is it not the best way to operate the system?

Would it be better to have it run continuously for longer periods of time? Or does it matter and either way is fine? Thank you again for your help and patience. :-)

On 2020-12-28 - by (mod) - boiler may run nearly continuously in very coldest weather

John

That sounds perfectly reasonable to me. You may find that on the coldest days of the year your heater is running almost continuously but on other days it should be running at a much smaller percentage of the time just as you described.

On 2020-12-28 by John H - boiler cycles on-off every 2-12 minutes

I bought a home with hydronic floor heat (it was built in 1999). It's a one-story on a slab and has no basement. The system is one zone and serves the entire house (~1400 square feet) and the insulated 4-car garage. There is only one thermostat for it that I currently use as an off-on switch.

I've never before had a hydronic system and don't really know whether I'm operating it in the best way, and am hoping you can provide insight. I currently have it set up to provide 80 degree water to the floor piping and run it 24 hours per day, 7 days a week starting in mid-October through April.

The boiler cycles, burning for about 2 minutes and is off for about 12 minutes - so the total burn time per day for the boiler is 4-5 hours. Is this a "good" operating scheme or would it be better to run the boiler constantly for two 2.5 hour intervals during the day, and increasing the water temperature water so the boiler is operating continuously?

Operating it as I do does keep the floors comfortably warm through the winter and the ancillary heat (electric forced air) only operates infrequently - usually when the outside temperature is at or below 0 degrees F.

Thank you for any help you can offer.

On 2020-09-28 by Linda

thank you for your rapid response. I'll contact an experienced radiant heat floor installer and pursue having the slab checked for insulation.

On 2020-09-26 by mod) - how to add a radiant heating system on top of an existing concrete slab floor

ThermoSoft's ThermoTile electric radiant heat flooring mat cited & discussed at InspectApedia.com ... ThermoSoft's ThermoTile electric radiant heat flooring mat cited & discussed at InspectApedia.com

Linda

There are certainly radiant floor heat systems that can work perfectly well on top of a slab, covered by new flooring; the exact process and choices will depend on what kind of finish flooring is in mind and on the need for furring strips and a new layer of subfloor over the slab.

Those include hydronic radiant heat floor systems - tubing set atop the existing floor, over which a new floor is placed, perhaps using furring strips, subflooring, finish flooring, and electrical radiant heating systems that can be installed similarly.

Thin film radiant heat systems, other electric radiant heat floor systems as well as hydronic or hot water radiant heat flooring systems are described on this page and at the

RECOMMENDED READING links at the end of this article.

Shown here is ThermoSoft's electric radiant heating mat, sold in 15 square-foot sections and that is used under ceramic or stone tile finish flooring.

Start by asking for guidance from an **experienced** radiant heat floor installer in your area.

She may want to investigate under the slab to see what sort of insulation is there and if necessary she may want to add insulation before adding the radiant heat system.

Here are examples of electric radiant heat flooring systems

On 2020-09-26 by Linda

I read your fascinating article on installing radiant heat systems when pouring slab foundations;

however, I'm in the process of purchasing a house with an existing slab foundation, built in 1974, and no history of whether insulation or vapor barriers were installed at the time.

I'd like advice on how to add a radiant heating system on top of the floor, with the intention of replacing the flooring currently in place.

On 2020-05-14 by Connie

Thank you for your help. As for the framing in shed it is block walls and trailer frame for rafters, very little wood. Have a great day

On 2020-05-13 - by (mod) -

Insulation will help wherever you put it; outside, be sure you don't provide a path for carpenter ants or termites up into wood framing.

On 2020-05-12 by Connie

We talked about trenching around the outside and insulating the wall down to footer. Inside is a little harder to insulate because of constant welding, grinding etc. Do you think placing insulated foam on outside wall would help? Hubby did lots of research on the in floor heat based on size of area for how many lines needed.

On 2020-05-12 - by (mod) - Mini Broiler could not keep up with heating the floor

Good news is that it looks like the tubing may be high in the slab.

I cant assess whether or not the amount if tubing is sufficient.

But the glaring need for insulation on the block walls, a large source of heat loss.

On 2020-05-12 by Connie

We have a block building with poured walls that we placed in floor heating. There is no insulation on the walls.

There is insulation on the floor, think either 2 or 3 inches thick with three lines of pex fastened down in a pattern per specifications read.

Think concrete is about 3 to 4 inches thick, based on pictures taken and have on computer. Purchased a Mini Broiler and in floor thermostat. Hooked everything up and after a few issues like broken line needing fixed the heat was turned on.

Mini Broiler could not keep up with heating the floor so purchased a regular water heater and also a timer. Thermostat set at 68 degrees and the timer set to kick on every hour for 15 minutes.

Our electric bill for the building runs on average $400 during the winter. I told hubby he needs to figure out a more cost effective way of heating the building. Either figure out why the in floor heating is not efficient or perhaps not hooked up properly or that the building needs to be insulated etc.

He is so busy working a full time job as well as the part time job in shed so I am trying to be proactive before fall arrives again with no answers to our problem.

Everything was done quickly and not fully experimented with like bigger water heater and no timer. Any advice will be much appreciated.

On 2020-03-05 by Anonymous - you would not bother to run radiant heat under cabinets

Michael

Normally you would not bother to run radiant heat under cabinets and IMO even more important, not under a refrigerator, but if it does run there it's not a catastrophe.

Arguing: in very cold climates putting heat under a kitchen base cabinet were plumbing enters and drains exit might help prevent a freeze problem.

Counter-arguing: under a refrigerator a warm floor might cause the fridge to have to work harder to get rid of its heat, thus increasing its operating costs.

On 2020-03-05 by Michael Peters

Do you install radiant heat pex under refrigerator and kitchen cabinets?


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