Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality. Bookmark and Share
radiant heated hardwood flloors

Part I: Considering Radiant Heat?

Part II:
Installing hardwood floors over radiant heat

Part III:
Our Favourite Reference Book on Wood and Wood Flooring

Part IV:
Wood is Good by Dr. Joseph Lstiburek, P.Eng.,

Court sides in favour of the defendants - chalk one up for the consumer and radiant heating under hardwood floors...

Court finds in favour of defendant over cupped floors

Cape Breton Flooring Ltd. v. MacLeod, 2012 NSSM 25

Visit our comprehensive bibliography on radiant cooling and heating.

See also:
Recommended floor temperatures for bare feet and for those wearing shoes

Visit this link for a slide show on mechanical schematics and architectural details. Allow 45 to 60 seconds to load

NEW: Advanced research into floor performance issues; The effects of heating systems on floor performance in cool temperate climates.

Original Source:
Forest and Wood Products Australia Limited, R. Farrell and S. Gadient

See Also:
Radiant Design Guide

Thanks to Carol Belcher and the Hardwood Manufacturers Association for letting us republish this material.

Radiant floor heating and hardwood floors work great together when building professionals and clients  work great together!

You are welcome to download this free slide presentation:

Radiant Heated Hardwood Floors
Guide to Hardwood Floors and Radiant Heating
(.pdf slide show)

Moisture and Wood. Suggested reading
For further information on moisture and wood, please download the following documents courtesy of the Canadian Wood Council.

Moisture and Wood-Frame Buildings

BP-1 Moisture and Wood-Frame Buildings

Managing Moisture and Wood

 BP-6 Managing Moisture
and Wood

For more information on
wood in construction visit

Useful Reference and Design Documents from Dr. Joseph Lstiburek, P.Eng., Building Science Corporation

Relative Humidity

 Radiant Heating and Hardwood Floors is about Controlling Humidity

Dehumidify Air

Dehumidification for Radiant Systems

Read more about humidity in your home.


Radiant Floor Heating and Hardwood Floors:

Notice: We're running it again, Integrated HVAC Engineering: Mastering Comfort, Health, and Efficiency. 

For additional support visit our visitor services page.

New articles
Thermal Comfort: A 40 grit perspective for consumers
Built to code: What does it mean for consumer thermal comfort?
Thermal Comfort: A Condition of Mind

We've made these next pages on heated hardwood flooring available to make sure industry and consumers alike get the facts on using radiant heating.  For those who continue to spread myth #9 that radiant damages hardwood have you ever considered exactly 100% of all hardwood floor complaints in homes heated exclusively with hot air  - did not have radiant floor heating to blame...let us repeat - 100% - that would be all of them had problems unrelated to floor heating...keep reading.

Wood as a hygroscopic material - changes in moisture results in a change in dimension.

Wood - a hygroscopic and anisotropic material
Coloured scanning electron micrograph (SEM) of a block of wood from an elm tree. At top is a transverse section and at bottom is a longitudinal section. Xylem vessels (larger tubes) transport water and mineral nutrients from the roots throughout the plant. Its thick lignin walls also provide structural support for the stem. Due to woods cell structure a change in moisture content results in a change in dimension.
Image credit: Andrew Syred/Science Photo Library

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What do wood experts and material scientists have to say...


"Virtually all problems with wood-based building materials are moisture problems."
Wood Myths: Facts and Fictions About Wood, P. Fisette, Building Materials and Wood Technology, University of Massachusetts Amherst, 2005

"The equilibrium moisture content of materials is almost solely dependant on relative humidity and is largely unaffected by temperature."
Understanding Psychrometrics, Donald P. Gatley, P.E., ASHRAE Publications

"Wooden floors over UFH can perform well, and could even be argued that a wooden floor installed and operated correctly will out-perform those with conventional heating systems that cause hot-spots in the floor with extreme localised dimensional change. A wooden floor with UFH operated with moderate and gradual temperature changes will apply constant and even heat to the floor avoiding problems associated with localised heating."
The effects of heating systems on floor performance in cool temperate climate, R. Farrell, S. Gadient, Centre for Sustainable Architecture with Wood.

"Dimensional changes in wood are commonly observed but are not always recognized as the inevitable consequence of moisture changes in the material."
National Research Council Canada, Building Science for a Cold Climate,
N.B. Hutcheon, G.O.P. Handegord

"The relative humidity in the ambient air determines the equilibrium moisture content of materials; the vapour pressure determines the movement of vapour."
National Research Council Canada, Building Science for a Cold Climate,
N.B. Hutcheon, G.O.P. Handegord

"...wood expands and contracts in direct proportion to the amount of moisture contained in its cell walls, changes in dimension occur only below the fibre saturation point, when the cell walls begin to dry out."
Wood frame envelopes, Best practice guide, building technology,
Canada Mortgage and Housing Corporation.

My advice is don’t freak out about the heat especially in modern high performance buildings: typically the fluid temperatures in a properly designed floor heating system when controlled properly will be lower than the temperature of your blood with the surface temperatures operating at or lower than the temperature of your skin.
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Courtesy of the Hardwood Manufacturers Association

Part I : Considering Radiant Heat?

Infloor Radiant Heating for Hardwood FloorsThanks to advances in the heated floor industry, you can install hardwood floors over radiant heat - with confidence. That means you can enjoy the natural beauty of oak, ash, cherry, maple, hickory, walnut and other fine hardwoods and the comfort and efficiency of radiant heating.

The York family chose cherry floors and radiant heat for the recent 1,500-square-foot expansion of their 250-year-old farmhouse in central New Jersey. "I like warmth under my feet," Susan York says. "If my feet are warm, I'm comfortable."

York has allergies and was eager to avoid some of the dust blown about by a traditional forced-air heating system. The cherry floors and radiant heating system were chosen for the new great room, kitchen, dining room and office in the colonial-style home in Asbury, NJ. York believes the choice will boost her home's resale value.

"I think buyers today are more concerned about the quality of the air inside the house," she says.

As early as 60 AD, the Romans discovered one way to heat an enclosed space is to introduce heat below the floor surface and let it radiate upward into the structure (see updated history).

Millennia later, radiant heating is more energy-efficient than conventional forced-air heating systems. Some manufacturers say their radiant heating systems will cut energy bills by 20 to 40 percent by avoiding the heat loss associated with forced-air systems. In most buildings, heat loss is greatest in the top half of the rooms and that's where heat is concentrated with forced air heating systems.

(A note from RB on energy consumption: Building efficiency is the determining factor in energy consumption. Consumers are advised that efficiency saving in the magnitude stated above are only possible when mechanical, electrical and building efficiency are addressed.)

How Radiant Heat Works

Experienced installers of radiant heating systems and hardwood floors work together to choose the system that best suits your needs. Electric systems use thin electric mats that work much like electric blankets. They often are used to heat small rooms like kitchens, bathrooms and entryways. Larger rooms often justify the more costly initial expense of installing a hydronic system, which involves heating water that runs through plastic tubes under the floor. Hydronic systems can be powered by gas, oil, electricity or solar energy.

Radiant heat systems use a three-stage process to convey heated water to its destination.

  • A water heating system - comprising a standard boiler, water heater, heat pumps or geo and solar thermal - warms the water.

  • A series of controls then pumps the heated water through a tubing network that is installed in the subfloor.

  • As the warm water moves through the tubing network, it releases its energy and returns to the boiler system to be reheated. This makes for smooth and gentle temperature variations.

Hydronic radiant heat systems can be installed in just one room or throughout a new or existing home. A plumbing and heating contractor typically performs the work in conjunction with a flooring installer. Most radiant heat system manufacturers will provide the names of contractors in a given area.

The recommended maximum surface temperature for any floor is 85 degrees. Make sure your installer chooses a control strategy that assures this limit will not be exceeded, and gradually takes the floor through temperature changes.

Natural hardwoods warm quickly and are cozy for bare feet because they conduct heat more efficiently than thick, padded carpets. Solid hardwood or engineered wood floors work fine with today’s high-tech radiant heat systems – whether on subfloors or concrete slabs. You can add inlays to new or existing wood floors over radiant heat and you also can paint and stencil the floors.

What about tropical woods?

The Radiant Panel Association, a trade organization for the radiant heating industry, warns against pioneering the use of a wood with little information on its dimensional stability. If you’re importing a tropical or exotic wood, you must pay close attention to the source and age of the wood as well as the method used in drying it. Quick drying creates stresses that can affect the wood later as it expands and contracts.

Which hardwood floors work best?

Extensive laboratory testing by Launstein Hardwood Floors in Mason, Mich., found that American hardwoods – including cherry, oak, ash, maple, hickory and walnut – are good choices for radiant-heat flooring.

For best results, use narrow boards, preferably not wider than 3 inches. Narrow boards will better accommodate wood’s expansion and contraction across a floor.

Consider using quarter-sawn wood for planks wider than 3 inches, regardless of species, for enhanced dimensional stability.

The Launstein testing found that quarter-sawn planks up to 7 inches across (when properly installed) can work well with radiant heat systems.

The testing also found that hardwood flooring that is three-eighths of an inch thick conducts heat better than thicker floors and resists gapping.

Installation Tips (click here for illustrations of other heated floors)

Wood naturally expands and contracts to reach balance with the relative humidity of its surroundings. That’s why it’s important to avoid installing wood flooring when moisture levels typically rise sharply, especially during painting or the installation of sheet rock. When radiant heat is installed in concrete, mortar beds or gypsum cement, operate the heating system until these are completely dry before topping with wood floors. This can take several weeks.

Before hardwood floor installation, operate the heating system until the relative humidity in the space stabilizes to the average level expected for seasonal conditions in the area in which the wood floor will be installed. For example, if the space is expected to average 30 percent relative humidity in the winter and 50 percent in the summer, the average would be 40 percent. In especially dry regions like the American Southwest, a humidifier may be recommended, according to Robert Rohr, owner of Maxrohr, Inc., a radiant heat system installer in Rogersville, MO. Likewise, a dehumidifier may be called for in especially humid climates.

Experienced flooring installers will ensure that the wood floor’s moisture content is appropriate for your area. A 6 to 8 percent moisture content is average in most parts of the country.

Care and maintenance

Caring for a hardwood floor with radiant heat is no different than caring for any other hardwood floor. Radiant heat systems also typically have no effect on refinishing guidelines. (It is, however, always best to check with the finish manufacturer.)

Part II: Installing hardwood floors over radiant heat

Republished with permission(c)2001-2005 Hardwood Manufacturers Association

see: Washington State University Civil and Environmental Engineering department has some good animations showing how wood changes with moisture content.
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100% of all hardwood floor complaints in homes heated exclusively with forced air did not have radiant heating to blame...learn why.

Learn more about designing radiant heating systems
Learn more about using finite element analysis (FEA) and Excel(TM) to validate radiant heating and cooling designs.

Suggested reading for consumers and office workers:
How to "ball park" your budget for indoor climate control.
Built to code: What does it mean for consumer thermal comfort?
Indoor environments: Self assessment
Thermal Comfort: A 40 grit perspective for consumers
The Total Comfort System - The "Un-minimum" System
Thermal Comfort: A Condition of Mind
Do-It-Yourself HVAC - Should you do it?
The Cost of HVAC Systems - Are You Paying Too Much for Downgrades?
Radiant Installations - The Good, Bad and Ugly
Thermal Comfort Surveys - Post Occupancy, Part 1
Thermal Comfort Surveys - Post Occupancy, Part II

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