Radiant heat

What the test measures

Over radiant heat the figure that matters is how warm the floor gets, and how fast that changes. The heating system is designed to a maximum, and the floor product’s document sets the limit the design has to respect. NWFA’s installation guidelines put the floor surface this way:

Unless otherwise specified by the wood flooring manufacturer, the heat-loss calculations designed for wood flooring installations should restrict the operating temperature of the radiant heat system to never allow the surface of the installed wood floor to exceed 80°F.

NWFA Installation Guidelines, Revised © 2025, p. 98 (PDF p. 102)¹

Manufacturers’ documents set their own figures, and some measure at a different place than the floor surface. The table under Red flags shows both, with NWFA’s figure beside the manufacturers’ at its foot.

What a valid report looks like

A complete record names, at minimum:

• the heating system: hydronic or electric, and its controls and floor sensor;
• the maximum operating temperature it was set to, and where that temperature is measured;
• the date the system was started, and the test results its installer handed over;
• the floor temperature readings, with dates and places;
• the air temperature and relative humidity in the room;
• the product document the figures were compared with.

NWFA’s installation guidelines also set out what the heating side should hand over. Where a record says what was done, these are the points to hold it against, quoted from NWFA:

Heat-loss calculation

“The radiant heat system design engineer and radiant heating system installer should make available a room-by-room heat-loss calculation based on all of the factors that will affect the heat output of the radiant system.”¹

Maximum operating temperature

“This analysis must establish a maximum operating temperature of the heating system dependent on the floor covering being installed over it.”¹

Hydronic systems

“Water-heated (hydronic) radiant-heat systems should be pressure tested, all system controls should be fully operational, and functional operating results should be made available by the system installer.”¹

Electric systems

“Electric underfloor systems should be tested for proper operation, and functional operating results documented and made available to the wood flooring installer by the heating system installer.”¹

Before delivery

“All radiant heating systems should be fully operational, regardless of season, for a minimum of 5 days prior to delivery of wood flooring.”¹

Across the floor

“The wood floor surface temperature should vary no more than 3°F at any point within the installed wood floor.”¹

From day to day

“The floor should not fluctuate by more than 5°F per day.”¹

This is NWFA’s guidance, not the floor document’s; where your product’s document describes radiant heat, that document applies.

Red flags

NWFA’s installation guidelines are an industry guideline, not the document for your product. Where the two differ, both are shown above.

1. Hardwood: the record compares the floor temperature with NWFA’s figure alone. For engineered hardwood, NWFA’s guideline and the manufacturers’ documents give different figures; both are at the foot of the table, and NWFA’s sentence is under What the test measures.

2. Glue-down LVT: the reading is a floor-surface temperature. In the table, glue-down LVT reads 85 °F in each of the 3 documents; one of those documents sets its limit at the adhesive, under the floor, not on top of it:

   Planks / tiles may be installed over underfloor heating systems, but these must be constructed so that the temperature at the adhesive interface does not exceed 85°F (27°C) ensuring the correct adhesive is used.

   Karndean Gluedown Installation Guideline USA, KD80333GLO | October 2023, PDF p. 3⁸

3. Any floor type: the system was not running before the flooring arrived. NWFA’s sentence is under What a valid report looks like, with the hand-over it expects from the heating installer.

4. Any floor type: the room is on a set-back or programmable thermostat. NWFA:

   “Set back” or programmable thermostats could vary room temperature greater than 5°F per day, and should not be used.

   NWFA Installation Guidelines, Revised © 2025, p. 98 (PDF p. 102)¹

5. Solid hardwood: the record assumes the product may go over radiant heat. None of the solid hardwood documents read publishes a temperature limit; the row says so. 4 of them advise against or do not allow radiant heat for their own product, each in its own words, listed below. Whether a product may go over radiant heat at all is its manufacturer’s call. NWFA:

   Follow the flooring manufacturer recommendations as to whether or not each specific product is intended to be used over radiant heat.

   NWFA Installation Guidelines, Revised © 2025, p. 99 (PDF p. 103)¹

   The limit that binds you is in your product's installation document.

Solid hardwood documents that advise against or do not allow radiant heat for their own product

From Bruce Solid 3/4" Strip and Plank:

NOTE: Do not install this product over Subfloors with Radiant Heat.

Bruce Solid 3/4" Strip and Plank, LA-295726-120, © 2020, PDF p. 1¹⁷

From Mullican Solid Wood Flooring Installation:

May NOT be installed over subfloor radiant heating systems.

Mullican Solid Wood Flooring Installation, PDF p. 1¹⁸

From Mirage Installation Guide, Solid Prefinished Hardwood Floors (Mirage Classic):

Mirage does not recommend installation of Mirage Classic floor over radiant-heated subfloor.

Mirage Installation Guide, Solid Prefinished Hardwood Floors (Mirage Classic), PDF p. 2¹⁹

From Expert by Lauzon Limited Warranty and Installation Guide, under "Installation Over a Radiant Heat System":

Only recommended for engineered floors

Expert by Lauzon Limited Warranty and Installation Guide, October 2025, LII-MK-ST-874-C, PDF p. 7¹⁵

Questions to ask the installer

1. Does my product’s installation document allow it over radiant heat, and what limit does it give?
2. Where is that limit measured: at the floor surface, the subfloor, or the adhesive?
3. What is the system’s maximum operating temperature, and who set it?
4. When was the system started, and what test results did the heating installer hand over?
5. What thermostat and floor sensor control it?