Heated Hardwood Floors

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Heated Hardwood Floors Installation Guidelines


heated wood floors heating systemIf you're looking for the best floor heating systems for heated hardwood floors, Krell Distributing provides custom radiant floor heating to provide the comfort of heated floors with a system that's made for your home.

Heated Hardwood Floors With Radiant Floor Heating

Radiant heating is a growing source of energy in North America, both in residential and commercial installations. Consequently, it’s important for installers to understand how radiant heating works as a solution for heated hardwood floors. Floor heating can be the perfect option for you, but you’ll want to know exactly how heated hardwood floors work first.

How Does Radiant Floor Heating Work With Heated Hardwood Floors?

Radiant heating does not heat air directly as do more conventional forms of heating, such as baseboard convectors or forced air circulation. Radiant heat is "omni-directional." Unlike warm air, which tends to rise, radiant energy travels in all directions. A large area of mild surface temperatures, such as a warm floor, is capable of transferring as much heat as a small surface area, such as a steam radiator, at high surface temperatures.

Radiant heat beneath wood flooring for heated hardwood floor solutions involves tubing in concrete, or underfloor heating.

How Radiant Heat Works For Heated Hardwood Floors

The most important factor in a successful installation for heated hardwood floors over radiant heat is a dry slab and a dry subfloor. The only sure way to dry a slab and underfloor heating system is to turn on the radiant heating system before installing the wood flooring. If this isn’t done, moisture left in the slab will enter the heated hardwood floors as soon as the heat is turned on. The result are floors that will expand, contract, shrink, crack, cup, and bow excessively. If the heat can’t be turned on, then everyone involved – down to the homeowner – should understand and accept the compromises that will appear down the road.

How Long Should the Heat Be On For Heated Hardwood Floors?

Opinions on the amount of time required vary widely. Some say the heating system should be turned on at least 72 hours before installation, with a preferred time of five to six days. That assumes that the slab has been in place for at least 60 days. If the slab is relatively new, the recommendation is to have the heating system turned on for 30 to 60 days before installing wood floors. As always, follow the recommendations of your wood flooring manufacturer.

Wood dries rapidly when the heat is first turned on. It dries to a lower moisture content toward the end of the heating season. When the radiant heat is turned off, moisture once again starts to seep into the wood subfloor and radiant slab. Abruptly turning on the radiant heat in the fall will subject heated hardwood floors to rapid and easily noticed movement. Evidence of this movement will be cupping or crowning of the boards. Finally, shrinkage cracks will appear between individual floorboards. Alternatively, gradually turning the heat on before the first really cool day will begin the seasonal movement more gradually. Thus, the movement of the heated hardwood floors will be much less noticeable. As always, humidity controls can help offset flooring expansion and contraction.

The Type of Wood Matters for Heated Hardwood Floors

Not all species of wood are good candidates for an installation over radiant heating. It’s best to follow the manufacturer’s recommendation for a species’ suitability over radiant heat. When possible, choose a species that is known for its stability for your heated hardwood floors. Quartersawn or rift-sawn flooring is preferable to plainsawn in the search for stability. Strip flooring is also a better choice than plank flooring, because narrow boards expand and contract less than wide boards do. Using narrow boards also means there are more seams in a floor to take up movement. Because of its dimensional stability, laminated flooring is another good choice.

Radiant heating systems are currently designed to run cooler than they did years ago, although water supplied to the systems generally range from 90 degrees to 140 degrees. In years past, when water temperatures exceeded 140 degrees, wood fibers in heated hardwood floors were repeatedly traumatized, causing stress fractures, gaps, and twisting. Repeated heating and cooling also broke down the adhesive that bonded the hardwood to the slab.

Radiant Heat Installations For Heated Hardwood Floors

With radiant heat, the heat source is directly beneath the heated hardwood floors, so the flooring may gain moisture or dry out faster than a similar floor in a home with a conventional heating system. Heated hardwood floors can be installed over radiant heat as long as you understand radiant heat and how it can impact wood flooring, what precautions to take, and what type of wood flooring to use. 

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Styles of wood flooring that are best for radiant heat installation for heated hardwood floor projects are as follows:

Laminated/Engineered Wood Flooring

is more dimensionally stable than solid wood flooring.

Floating Floors, Laminated/Engineered or Solid tend to move as a unit to help accommodate moisture content changes.

Certain species

are known for their inherent dimensional stability such as American Cherry, American walnut, mesquite, teak and others. Other species such as maple and Brazilian Cherry are unstable species for heated hardwood floors with a radiant floor heating system. See: Wood Floor Species chart.

Quartersawn or Rift Sawn Wood Flooring

Quartersawn wood flooring is more dimensionally stable than plainsawn wood flooring. Narrow boards- (2¼"(56.7mm) or less, are the best choice of solid wood flooring over radiant heat.

General Radiant Heat Installation Guidelines For Heated Hardwood Floors

See manufacturers of wood floor products suitable for radiant heat.

To minimize the impact of fast acting changes in temperature and the resulting effect on heated hardwood floors, Krell Distributing recommends the installation of an outside thermostat. If an outside thermostat is not part of your radiant floor heating system for your heated hardwood floors, we suggest that an outside thermostat should be considered. Our heated hardwood floor systems aren't like conventional heating systems that switch on the heat when it becomes cold. Because of this, our radiant systems provide more efficient heating. These gradual, small increment based heating changes related to outside temperatures result in fewer changes to the wood floor (such as shrinking and cracking, among others).

The subfloor of your radiant heating system should have the appropriate moisture test to comply with standards in the trade.

Krell Distributing recommends that a 6-8 mil polyethylene vapor barrier is installed over slab radiant heat systems. We also recommend that all seams are taped during installation to ensure the barrier is tight. To safeguard the barrier from rips, some contractors lay 1/16" (1.5625mm) thick foam sheeting over the vapor barrier.

When the slab has cured, we recommend that the heat should be turned on no matter the season. This heat should be left on for a minimum of 5-6 days prior to the wood flooring being installed.  

The following installation systems can be used successfully over radiant heat:

  • Glue Down
  • Direct Nail To Subfloor
  • T & G Direct Nail To Sleepers
  • Single Layer Of Plywood On Sleepers
  • Double Plywood Floating 6. Floating Solid/Clip
  • Floating Engineered/Laminated


Glue Down Engineered/Laminated Or Parquet:

  • (Limited Borders, Height Can Be Kept To A Minimum, Can Get Some Movement On Solid Slab)
  • Glue Laminated Flooring
  • Install Over Approved Sub-Floor- Engineered/Laminated Unfinished/Prefinished/Impregnated.
  • Can Be Glued Direct To Approved Subfloor. Glue Direct Is Not Recommended On Lightweight Slab (Less Than 3,000 Psi).
  • The Heating System Has To Be Turned Off Before Gluing.
  • Use Adhesive Approved By The Wood Manufacturer.
  • Maximum Surface Temperature – 85 Degrees F (29.44 Degrees C).
  • Expect Some Heating Season Separations.


Direct Nail to Sub-Floor For Heated Hardwood Floors

heated hardwood floor typesTYPE 1:

  • Heating Tubes Are Stapled To The Underside Of The Wood Sub-Floor, Between The Floor Joists.
  • Must Have An NWFA Approved Sub-Floor For Wood Flooring.
  • Solid Wood Must Be Properly Acclimated For Heated Hardwood Floors.
  • Be Sure Nails Are Not So Long As To Penetrate The Tubing.
  • All Other Installation Procedures Are The Same, Strip-Unfinished/ Prefinished – Solid.


TYPE 2:

  • A Sandwich System, The Pipes Are Laid Between Sleepers Over An Existing Wood Sub-Floor. A New Wood Sub-Floor Is Then Nailed To The Sleepers.
  • Must Have An Approved NWFA Sub-Floor For Wood Flooring.
  • Solid Wood Must Be Properly Acclimated.
  • Be Sure Nails Are Not So Long As To Penetrate The Tubing.
  • All Other Installation Procedures Are The Same, Strip – Unfinished/ Prefinished – Solid

T & G Direct Nail To Sleepers:

  • Must Choose Direction Before Sleepers Are Installed.
  • Sleepers Should Be 2X4′ Or 2X3′, Group 1 Density Pressure Treated Kiln Dried Lumber, 12′(300mm) On Center.
  • Use 2 ¼" (56.25mm) Widths Or Less For Solid Wood Flooring.
  • Solid Wood Must Be Property Acclimated.
  • Cannot Use Shorts.(18" Or Less Pieces)
  • Expect Some Heating Season Separations
  • All Other Installation Procedures Are The Same , Strip -Unfinished/ Prefinished – Solid.

Single Layer Of Plywood On Sleepers:

  • (Allows For Borders With T & G, Increases ‘R’ Factor, Raises Finished Floor Height, Makes Nailing Easier, Can Use Shorter Hardwood Lengths)
  • Sleepers Will Be Embedded In Concrete With Only Tops Showing.
  • Install Approved Vapor Barrier (6-8 Mil Polyfilm).
  • Fasten Plywood To Sleepers According To NWFA Guidelines, Strip Unfinished/Prefinished- Solid.
  • Creates A More Level Surface.
  • Expect Some Heating Season Separations.


Double Plywood Layer Floating With T & G:

  • (High ‘R’ Value, Can Use Borders, Makes Nailing Easier, Can Use Shorter Hardwood Lengths)
  • Sleepers Are Unnecessary.
  • Use NWFA Approved Subfloor Guidelines For, Strip Unfinished/Prefinished – Solid.
  • Solid Wood Must Be Acclimated According To NWFA Guidelines, Strip Unfinished/Prefinished – Solid.

Floating Solid With Clips:

  • (Easy To Install, More Expensive, Short Stave Construction, Solid Floating, Easy To Remove E.G. Leased Rental Space, Slight Noise Reduction)
  • Expansion And Contraction Is Noticeable.
  • Multi Butt Ends Join Together.
  • Use An Adhesive Approved By The Wood Manufacturer For Joints.


Floating Engineered/Laminated:

  • (Easy To Install, Comes Prefinished And Unfinished, Limits Finished Height, Slight Noise Reduction, "R’ Value Increases) – Limits Expansion And Contraction.
  • No Cracking When Slab Cracks.
  • Multi Butt Ends Join Together.
  • Use An Adhesive Approved By The Wood Manufacturer For Joints.
  • Subfloor Should Be According To Manufacturer’s Recommendation, Engineered/Laminated -Unfinished/Prefinished/Impregnated.


Krell Distributing also stocks "Low-R" Carpet padding for radiant floor heat with carpeting.

Get Heated Hardwood Floors With Radiant Floor Heating

With over 200 years combined experience, Krell Distributing has the resources and knowledge to help you complete your heated hardwood floor project. We offer continued technical support and competitive prices on floor heating.

Contact us for more information or to set up a meeting.