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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.
Tongue-and-groove strips are recommended
and beveled-edge boards show fewer seasonal gaps.
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
after installation.
Installation
Details
Subfloor
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 choices.
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.
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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.
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The
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.
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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 mass benefits. |
Climate Control Measures
The following climate controls will minimize expansion
and contraction during and after installation of the floor:
Floor Temperature:
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.
Tube Installation:
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.
Mechanical Humidity Control:
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.
Heat Transfer 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.
Exterior Thermostat:
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. y.
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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