The benefits of infloor heat
Once you shed your fuzzy slippers and discover the
comfort of warm floors, you'll be sold. Heated floors,
often called radiant floors, offer benefits beyond foot
comfort. They keep entry and bathroom floors dry
and provide space heating in cold rooms. You can
even turn down the thermostat for your central heating
system and still keep some rooms warmer.
In this article, we'll walk you through the types of
radiant floor systems you can install in your home.
We'll tell you the pros and cons, and show you key
installation techniques. This will help you decide
whether to take on the project yourself or hire a
professional. These heating systems are most often
installed under ceramic tile in bathrooms, but keep
in mind that you can add heat under any type of
flooring material (see “Floor Coverings and Heated
Floors,” below). All floor heating systems warm the
floor with either electricity or hot water.
Electric systems are simple and affordable
Electric floor systems work just like an electric blanket:
Electricity runs through “resistance” cable and creates heat.
Because electricity is fairly expensive, relatively few homes are
entirely heated by in-floor electric systems. However, these systems
are great for making especially cold floors foot-friendly.
They also boost the temperature in an otherwise chilly room by
a few degrees. The warm floor in a bathroom makes getting out
of the shower a cozier prospect on a cold day. That's the payoff.
Electric systems have three components: heat cable, a thermostat
and a temperature sensor (Figure A below). The thermostat is
connected to the home's power supply and turns the heat on
and off according to the floor's (not the room's) temperature. A
sensor installed in the floor along with the cable tells the thermostat
how warm the floor is. (Most people prefer a floor temperature
of 80 to 90 degrees F.) The thermostat and sensor are
packaged together; cable is usually sold separately.
Don't use a thermostat from one manufacturer with cable
The electrical connections require only basic wiring know-how,
and laying the floor cable is a DIY-friendly project. Because
of this easy installation—and the lower cost of materials—an
electric system is usually the best choice for small-scale projects
like heating a kitchen floor or warming up a cold bathroom.
Adding electric heat to a typical bathroom when you install a
new floor adds only $200 to $300 to the cost of the project.
Operating costs are typically about a half cent per square foot
Often the biggest challenge is “fishing” electrical cable
through finished walls to the thermostat and cable. Since these
systems generally draw only 10 to 15 watts per sq. ft., you can
usually connect them to an existing circuit to heat a typical
bathroom. For a larger room, you may have to run a new cable
to the main panel and pay an electrician about $120 to connect
the new circuit there.
If you're installing heat over a
wood-framed floor, place fiberglass
insulation between the joists
to drive the heat upward. The system
will work fine without insulation
but will be more efficient
with it. Before you install an electric
system over a concrete floor,
check the manufacturer's instructions—
they may require a layer of
foam insulation over the concrete
before the heat cable is installed.
Tip: When you estimate
the square footage
of a room, include
only the areas
where you can walk;
it makes no sense to
heat the floor under
behind the toilet.
Figure A: Electric floor heat details
Figure A: Electric Floor Heat
The cable generates heat and warms the
floor. A thermostat connected to a sensor
controls the temperature of the floor.
Electric system #1: Loose cables ($3 to $6 per sq. ft.)
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Photo 1: Thin-set mortar technique
String cable between end channels and fasten the cable to the
floor. Screed thin-set over the cable to create a flat surface.
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Photo 2: Self-leveling technique
Install plastic lath and loose cable. Pour self-leveling compound
to embed cable and create a perfectly flat, smooth surface.
The cable comes on a spool, just like any other wire. Loose cable
is by far the cheapest way to heat a floor and it's just as effective
as the other systems. The drawback of loose cable is installation
time; you have to position the cable in a serpentine pattern, fasten
it with lots of hot glue or staples, and then “embed” it.
Most loose cable systems include end channels that guide
spacing (Photo 1). You can place cables close together to
make the floor heat up faster and reach a higher temperature
or farther apart to use less cable. Manufacturers offer various
cable lengths to suit the floor's square footage. You can't splice
sections of cable together to serve a larger room or repair
damaged cable (this is true of all electric systems). Fasten the
cable every 6 in. so it can't shift or float while you embed the
Caution: Work carefully with your trowel. If you nick
the cable, the entire system won't work.
There are two ways to embed cable: You can install the cable
over tile backer board and then cover it with “thin-set,” the
mortar adhesive used for ceramic tile (Photo 1). The thin-set
shrinks as it cures, so you may have to add a second layer
after the first hardens to level it out. But creating a perfectly
flat, smooth surface with thin-set is difficult. You can make it
smooth enough for ceramic tile or a floating floor but probably
not smooth enough for vinyl flooring. For a faster,
smoother surface, install the cable without backer board and
pour on “self-leveling compound,” or SLC (Photo 2).
SLC is a cement-based powder that you mix with water and
then pour over the cable. It becomes rock hard in a few hours.
Reinforce the SLC with plastic lath; metal lath can cut the
cable. Covering your floor with a 1/2-in.-thick layer of SLC
costs about $2 per sq. ft., including the lath. You can then lay
tile, carpet, vinyl or a floating floor directly over the SLC.
Electric system #2: Mesh mats ($10 to $12 per sq. ft.)
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Mesh under tile
Cut mesh mats to fit the floor. Position mats with double-face
tape and fasten with glue or staples. Cover the mesh with
thin-set or self-leveling compound.
The cable comes already woven into a plastic net. The pre-positioned
cable installs quickly—in less than half the time for
loose cable. You simply staple or hot glue the mesh to the
floor. As with loose cable, you then embed the cable and mesh.
Mats are available in lots of different dimensions. You can
cut the mesh into sections to cover your floor or fit around
corners (photo). But you can't cut or splice the cable
itself. Some manufacturers recommend combing thin-set
directly over the mesh and setting tile all in one operation. But
this is difficult. Most tile setters prefer to embed the mesh first
with thin-set or SLC just as with loose wire. The mesh tends
to “float” as you embed it, so fasten it to the floor every 6 in.—
even if the instructions recommend less fastening. After
embedding it, you can lay tile, carpet, vinyl or a floating floor.
Electric system #3: Solid mats ($10 to $20 per sq. ft.)
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Photo 1: Under tile
Lay the mat over thin-set and force it firmly into the thin-set
with a grout float. After it hardens, comb more thin-set over
the mat to set ceramic tile.
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Photo 2: Under a floating floor
Lay mats over an existing floor and duct-tape them together.
Lay a floating wood or laminate floor directly over the mats.
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Photo 3: Under-floor technique
Staple mats between joists to heat the floor above. Then
insulate the underside of the mat with R-13 or thicker fiberglass
Solid mats are often the most expensive electric system, but
they're also the easiest to install. The cable is completely
enclosed in synthetic fabric, plastic sheeting or metal foil. The
big advantage is that you don't have to embed it as you do loose
cable or mesh mats. With some versions, you simply smooth the
mat onto a bed of thin-set (Photo 1). Then you spread more
thin-set over the mat and set ceramic or stone tile as you normally
would. Some solid mat systems are even easier to install;
you just roll out the mats, tape them together and you're done
(Photo 2). You can then lay a floating wood or laminate
floor directly over it.
Mats are available in various dimensions, and you can combine
mats of different sizes to cover your floor. Some mats are
sized to fit between joists, so you can heat the floor from below (Photo 3)—a big advantage if you don't want to replace an
existing floor. However, don't install electric heat under a subfloor
unless the system is specifically intended for that method.
Floor Coverings and Heated Floors
Any flooring material can cover a heated floor, but
some work better than others.
- Ceramic and stone
tile are the most common. Heat doesn't harm them
and they hold and conduct heat best.
- Solid wood floors can develop gaps if they dry and shrink
when heated. If you opt for solid wood, leave the
installation to an experienced pro who will test the
moisture content of the wood to avoid shrinkage.
- Floating floors made from wood or plastic laminate
don't develop gaps because they're not fastened
directly to the subfloor. But you'll have to limit the
floor temperature. Flooring warranties often limit the
temperature to 85 degrees F.
- Vinyl floors have
similar temperature restrictions, whether they're
sheet vinyl or tile.
- Carpets or rugs can go over a
heated floor, but they act as insulators and reduce
heat flow to your feet and to the room as a whole. If
you choose electric heat under hard flooring and plan
to use an area rug, consider installing the cables only
under the flooring that won't be covered by the rug.
Hydronic systems heat space as well as your toes
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Photo 1: Under-floor technique
Drill holes in joists and loop tubing between them. Install
metal plates to support the tubing and transfer heat. Insulate
with fiberglass batts.
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Photo 2: Channel technique
Install a channel system over a wood or concrete subfloor.
Press tubing into the grooves. Install a wood or floating floor
or add backer board for tile.
In a hydronic system (Figure B), heated water from a boiler or
a water heater runs through loops of flexible plastic tubing
called “PEX.” (PEX can be used for household water supply lines
too.) The hot tubes then heat the floor. The main advantage of
hydronic systems is that they generally deliver more heat at a
lower operating cost than electric systems. That's why hydronic
heat is usually a better option than electric systems to heat large
floor areas or even an entire house. However, because they usually
involve a boiler, a pump and gas lines, hydronic systems are
more complex than electric systems. You can install hydronic
floor heat yourself, but you need basic electrical and plumbing
know-how as well as professional design help. The materials for
a small-scale hydronic project will cost at least $600.
The easiest—and least expensive—way to install PEX is to
run it under a subfloor between joists using transfer plates and
insulation (Photo 1). This method costs less than $2
per sq. ft. for tubing, plates and insulation. To install PEX on top
of a wood-framed or concrete floor, you need to lay a grooved
channel system over the floor (Photo 2) or embed
the tubing in self-leveling compound (see Figure B). Covering
PEX requires more SLC than you can mix yourself; leave that to
pros who have special mixing and pumping equipment (at least
$2 per sq. ft. for the SLC only). With a concrete floor, you may
have to lay foam insulation over the slab before installing PEX.
In new construction, the tubing is often installed over insulation
and the concrete slab is poured over it.
A hydronic system requires several expensive components.
But several rooms share the components, so the more area you
heat, the lower the cost per square foot. If you want to heat 200
sq. ft. or more of floor, a hydronic system may cost less to install
than electric heat.
The heat source for a hydronic system can be a boiler or a
standard water heater. If your home is already heated by hot
water radiators or baseboard units, there's a good chance that
your existing boiler can handle the hydronic system as well. If
you don't have a boiler, a water heater can heat one room or several,
depending on the size of the water heater. If you're building
an addition, you may find that installing a water heater–powered
hydronic floor is less expensive than extending your existing
central heating system.
Aside from PEX, a heat source and a pump, a hydronic system
may require components such as electric zone valves. It
may also require additional pumps. You can install these components
yourself, but don't try to design a system yourself.
Look for a company that specializes in helping homeowners
plan and install hydronic systems. Before you choose to install a system yourself, get bids
from professionals. It will help you decide whether the money
saved is worth your time and effort.
Figure B: Hydronic floor heat details
Figure B: Hydronic Floor Heat
Self-leveling compound technique. A boiler
or water heater heats water, which is
then pumped through a loop of embedded
tubing. The warm water heats the floor.