Installing Hardwood Floors Over Radiant Heat
With advances in heating and insulation technology, and effective
management of wood's natural expansion and contraction, builders,
architects and designers achieve faultless installations of hardwood
flooring over radiant heat.
With hardwood flooring, the wider the board, the greater the
potential for gaps between the boards when they contract with seasonal
changes in temperature and humidity.
strips are recommended and beveled-edge boards show fewer seasonal
It is not recommended to use radiant floor heating under plank
flooring wider than 3 inches. Rift and Quartersawn Flooring, by
nature of its' manufacture is highly recommended for use over radiant
heat flooring systems.
How It Works
Radiant heat systems use a three-stage process to convey heated
water to its destination. (See diagram). A water heating system
that can be either a standard boiler, water heater, a geothermal
heat pump or even solar panels.
The heated water is pumped through a tubing network 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.
Good communication with the radiant heat system designer is critical.
Everyone should be notified of any work pertaining to the installation,
especially if specifications are changed. To ensure a superior end
product, pay attention to the following factors before, during and
Work with the system designer to choose the subfloor option (see
illustrations.) The heat system designer is responsible for the
subfloor installation, but you will want to be familiar with the
Direct contact of the tubing with the flooring is not recommended.
The subfloors shown here are recommended for hardwood floor installations.
Plywood (5/8") or oriented strand board (3/4") make good candidates
for subfloor materials in radiant installations. Particleboard subfloors
are not recommended by radiant heat companies.
Stapled Directly to Subfloor
is a method commonly used by Installers. The tubes are stapled
onto the subfloor which continuously releases heat to the
hardwood flooring above.
Sandwiched Over a Framed Flooring
approach is used when you do not have access under
the existing floor system or when the underside of the floor
cannot be used, such as a second story over a beamed ceiling.
Masonry Filled Sandwich over Framed
Floor with Fiberglass Insulation
is commonly used when access to the under-floor is
not possible. It also offers the fire resistance, sound
dampening and thermal mass benefits.
Masonry Filled Sandwich over Framed
Floor with Foam Insulation is is another technique
used when access to the under-floor is not possible. It
also offers the fire resistance, sound dampening and thermal
Climate Control Measures
The following climate controls will minimize expansion and contraction
during and after installation of the floor:
Provide the radiant heat system designer with the hardwood
flooring dimensions, species, and the desired temperature of each
room. This will give him/her the information needed to calculate
the necessary water temperature. The maximum surface temperature
of a wood 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.
Consult with the system designer to determine the tube network
layout, so you'll know where the tubes are before you nail down
the floor. It is best to have the tubing spaced evenly down the
joist cavity (between the sleepers). Then you can nail down the
finished flooring onto the sleepers on eight-inch centers. When
the tubing circuits are crossed over the center of the joist cavity,
have the system designer use nail plates to protect the radiant
circuits from being punctured.
The heating/ventilation/air conditioning
(HVAC) system should have mechanical humidity control. This will
monitor the room and keep the relative humidity at an even level,
which will keep the equilibrium moisture content of the floor stable.
Point Control: The system designer also should install
a set point control that will monitor the wood floor temperature.
The set point control should either reduce the system water temperature
or temporarily cycle the system off to prevent overheating the flooring
if equipment malfunctions.
An exterior thermostat is recommended to protect the
perimeter of the system from condensation absorption during the
spring and fall when rapid temperature changes may occur.
Once the subfloor, tubing and climate controls have been
installed, the heating system should run for at least 72 hours
to bring the house to the desired relative humidity.
Temporary, un-vented sources of heat - such as propane-fired "salamanders"
- can add excessive amounts of water vapor. Avoid them if possible,
but if they must be used, leave windows open to vent humidity.
Now follow the customary procedures for
installing hardwood floors.
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