This article includes discussion of installing radiant heat below both wood flooring and ceramic tile.
How to Install a Wood Floor Over Radiant Heating Systems
Radiant heating is a challenging application for wood floors due to the high temperatures, excessive drying, and greater temperature cycling to which the wood and finish
Careful monitoring and control of the moisture
levels of the flooring and structure at the time of
installation are critical for success. Also, because a 3/4-inch
wood floor over 3/4-inch plywood has an R-value of almost
2, similar to plush carpeting, wood systems generally must
run at higher water temperatures than tile or vinyl floors.
Large area rugs make it more difficult for the heating
engineer to design a system that will heat the room without
overheating the flooring.
Wood flooring can be installed over radiant slabs, or
over dry systems where the hydronic tubes are stapled
directly to the subflooring (staple-up) or laid on top in
Dry systems are more common in retrofits
and generally require water 10°F to 20°F higher than thin
slabs, leading to reduced efficiency, and often ruling out
low-temperature heat sources like heat pumps or solar.
Also, with less thermal mass than slab-based systems, dry
systems are more prone to temperature fluctuations.
radiant floor heating systems are designed to heat floors to about 80°F. Floors
heated above 85°F are uncomfortable for occupants and
may be damaged from the heat.
With any approach, the radiant slab or subfloor must
be dry prior to installation. With slab systems, run the heating
system for at least a week, up to three weeks if necessary,
to dry the slab to a moisture content of 8 to 12%
before installing the subfloor.
The subfloor and hardwood
floor should be acclimated to the average annual moisture
levels for the region and be within 2 percentage points of
each other (see “Acclimatization,” page 167). Flooring that
is installed too wet can lead to shrinkage cracks; flooring
installed too dry can lead to expansion problems or cupping
in humid summer weather.
To steer clear of problems, also follow these recommendations:
If possible, choose an engineered wood product rather
than solid wood. Floating floors are best, since they
are designed to accommodate movement.
If solid wood is used, avoid flooring wider than
3 inches—the narrower the better. If possible, use
quartersawn wood, which swells and shrinks
30%–50% less than flat-sawn.
Choose a prefinished flooring coated on all faces.
Prefinished flooring with chamfered edges
(microbevels) will help conceal shrinkage cracks.
Increase nailing of strip flooring to 4 to 5 inches
If finishing on site, use a recommended sealer to
reduce the chance of edge-bonding when the flooring
shrinks, leaving large gaps every several courses.
Always use a vapor barrier under the flooring, but do
not use asphalt-impregnated felt, which will give off
Avoid glue-down flooring. If used, make sure both the
flooring and adhesive manufacturers approve the
Specifications for Installing Radiant Heated Wood Floors over Slab-on Grade
Over traditional concrete radiant
slabs at least 4 inches deep, use either a floating hardwood
floor or install subflooring and nail on 3/4-inch strip flooring.
The subflooring can consist of two layers of 1/2-inch
plywood floating over the slab (see “Installing Over Concrete,”
page 168), or a single-layer 3/4-inch subfloor nailed
to the slab with powder-actuated fasteners. Because it
is thicker, the floating subfloor (Figure 5-15) will take
slightly longer to heat up, but it does not risk puncturing
the hydronic tubing.
Specifications for Installing Radiant Heated Wood Floors over Thin Slabs
In wood-frame construction, use a minimum
1 1/2-inch-thick slab of Gyp-Crete® or lightweight concrete,
which provides thermal mass for the radiant floor.
Above the slab use a floating hardwood floor, or nail strip
flooring to 3/4-inch sheathing installed over the lightweight
Fasten the sheathing to 2x4 sleepers placed
12 inches on-center, with the lightweight concrete and tubing
in between (see Figure 5-15 shown above). A two-layer floating
subfloor, as described above, is also an option for larger
rooms where the subfloor will be heavy enough to stay
solidly in place without nails.
Specifications for Installing Radiant Heated Wood Floors over Staple-up and Panel Radiant Floor Heat Systems
There are a variety of
dry radiant systems that install just under or over the subflooring,
making them ideal for retrofits. The tubing is
either stapled to the underside of the subflooring, laid over
the joists (with spacers to fur up the sheathing), or placed
over the subflooring in grooved plywood panels.
wood floating floors are best with these systems, but
nail-on hardwood flooring can work if installed with care.
This article series discusses and provides a best construction practices guide to the selection and installation of building interior surface materials, carpeting, doors, drywall, trim, flooring, lighting, plaster, materials, finishes, and sound control materials.
How to Install a Tile Floor Over Radiant Heating Systems
Ceramic tile should not suffer the same problems of curling, warping, gaps that may occur with wood flooring that we discussed earlier. But there are still some concerns to attend, including at least:
Effect of radiant floor heat on tile mastic or adhesive
Effects of radiant floor heat on some tile grout or on caulk used instead of grout at expansion joints and intersections ( do this or you'll be sorry later)
Protection of the slab against cracking that will telegraph up through the tile
Proper insulation below the slab and proper placement of tubing high in or over the slab. See RADIANT HEAT MISTAKES
Question: Install Tile Floor over Slab Using 3mm Polystyrene Sheets Under a Radiant Floor over Concrete
At last I found a website I can make sense of.
I need to replace my heating boiler and am looking at underfloor heating.
Your website gives me the information that I am as well to use particle board water pipe retainer than the expensive pre-constructed boards, I hope to find a 3mm polystyrene sheet (coffee cup type material) which can be placed between the existing concrete floor and the particle board before tiling on top of that.
Thank You for providing me with such useful information. - Anonymous by private email 2017/01/14
Thanks for the very nice note, Robert. We work hard to provide researched, unbiased and useful information so I'm really happy when a reader finds it so.
Now about that floor plan, let's research as much as possible before you do anything that's expensive, since as I document at RADIANT HEAT MISTAKES https://InspectAPedia.com/heat/Radiant-Slab-Heat-Mistakes.php it can be really ugly trying to un-do a radiant heat floor that was improperly installed.
at INSULATION R-VALUES & PROPERTIES we note that polystyrene board has an R-value of about 3.5 to 5 per inch. 3 mm is about 0.11 inches, giving an R-value of 0.3 to 0.5 - really not much in insulation. The material might also serve as a vapor barrier, since it's waterproof, and there's no reason not to also opt for a teensy bit of insulation too.
The thin material you describe is indeed readily available if you shop for it in packaging and wrapping materials. For example, companies selling packing and mailing supplies like Uline sell "UPSABLE Foam Rolls" that is flat, in thicknesses from 1/32" to 1/4" and in 12" and 24" widths. A 1/8" thick UPSABLE polystyrene foam sheet is 3.2 mm - about what you described.
Wider sheets of thin polystyrene sheeting is available from ULINE as well as other manufacturers. Wider rolls of this same material are sold in 48" rolls (about $165. U.S.D.) but that material isn't dead flat - which may not matter for your application.
I'm unclear on just how you plan to install, secure in place, and cover your radiant floor tubing.
I GUESS you are saying you're installing radiant tubing over a slab by using these layers:
Tile mastic - check with the manufacturer about the effects of radiant floor heat when using the mastic you choose
3/4" OSB or particleboard subflooring or 2 layers of 1/2" as per Steve's article
Radiant heat tubing - secured in place somehow
Thin polystyrene sheeting vapor barrier with modest insulating properties
Concrete with no insulation below the slab
Dirt or gravel - mother earth
Particularly, how do you plan to hold the tubing in place between the subflooring and the insulated slab?
at WOOD FLOOR RADIANT HEAT (above on this page) Steve Bliss describes such an installation with no insulation shown, though in new construction I would insist on insulating below the slab as well. Key is keeping the tubing as high as possible in the design. Steve used a full inch of plywood over the tubing set in the concrete. Your tubing, atop the concrete, will lose less heat into the concrete than Steve's design.
But I'm not sure about what the radiant heat tubing manufacturer will say about how the plywood bears directly on the tubing - is compression a concern?
In this design I'd give a call to the manufacturer of the tubing you plan to use. Ask for technical help from one of their engineers, and ask about your design and get her recommendations. Be sure to review the proper operating temperature range for the tubing too.
Please do keep me posted - what you learn will definitely help other readers.
Uline UPSABLE Industrial Rolls, ULINE, Uline
12575 Uline Drive
Pleasant Prairie, WI 53158 USA, Tel: 1-800-295-5510, Website: https://www.uline.com/BL_857/Uline-UPSable-Industrial-Rolls
Key articles on radiant heated floors
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FLOOR, WOOD RADIANT HEAT - guide to installing wood floors over radiant heat systems - this article is provided just below
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Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: email@example.com
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
2005 ASHRAE Handbook : Fundamentals: Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
"Insulation: Adding Insulation to an Existing Home [copy on file as /interiors/Insulation_Adding_DOE.pdf ] - ," U.S. Department of Energy - tips on how to do your own check for the presence of absence of insulation in a home
Insulation: Selecting Insulation for New Home Construction [copy on file as /interiors/New_Home_Insulation_DOE.pdf ] - , U.S. Department of Energy -
"Your state and local building codes probably include minimum insulation requirements, but to build an energy-efficient home, you may need or want to exceed them. For maximum energy efficiency, you should also consider the interaction between the insulation and other building components. This is called the
"whole-house systems design approach" [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] -
Insulation Types [copy on file as /interiors/Insulation_Types_DOE.pdf ] - , table of common building insulation properties from U.S. DOE. Readers should see INSULATION R-VALUES & PROPERTIES our own table of insulation properties that includes links to articles describing each insulation material in more detail.
Lath & Plaster Systems [copy on file as /interiors/LathPlaster_Nat_Gypsum.pdf ] - , 092300/NGC, National Gypsum Lath and Plaster Systems, National Gypsum Corporation, 800-628-4662 describing National Gypsum's Kal-Kore brand plaster base
Pergo AB, division of Perstorp AB, is a Swedish manufacturer or modern laminate flooring products. Information about the U.S. company can be found at http://www.pergo.com where we obtained historical data used in our discussion of the age of flooring materials in buildings.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones