HEATING / RADIANT IN-FLOOR HEATING
WHAT MAKES RADIANT HEAT DIFFERENT THAN FORCED AIR OR
In order to understand the benefits
of radiant floor heating, we must first realize the shortcomings of our
Most common heating
systems such as forced air furnaces use moving air (forced convection)
to deliver the heat to a room. There are some problems with this system.
First, hot air rises, therefore much of the heat ends up at the ceiling
while the floor remains cold.
Second, as air moves around the
room, it travels in warm and cool currents. We feel these drafts as the
air comes in contact with our skin.
Also, because the heated air
is delivered from only a few strategically placed registers, even
heating of the room is virtually impossible. There are inevitable warm
and cool spots within the room.
Forced air furnaces work in
blasts. The hot air is forced into the room for a short time and then
the flow of air stops. The air rises and spreads out, loses its heat,
and cools off. The room drops in temperature and the cycle repeats. This
causes temperature swings within the room as well as lower-level rooms
to be cool and upper-level rooms to be hot.
HEATING (HYDRONIC HEATING)
If you're like most people, you
probably assume that the warm floor heats air which rises to heat
people. This is only partly true. A small percentage of the heat
transferred to the room from a radiant floor actually comes from heated
air. In fact, the air temperature ceiling to floor and throughout the
room never varies more than one or two degrees.
question is then, "where does the heat come from?" Radiant heat is a
little more difficult to understand although we experience it daily. The
air in the big outdoors is primarily heated by its contact with the
heated earth. When we step outside on a warm cloudy day, the warmth we
feel is the radiant energy coming directly from the sun. It is exactly
that form of heat which is radiated from a warm floor.
energy is transferred through the air in all directions and is converted
to heat energy when it contacts an object such as walls, furniture or
people. It is a fact of nature that if one object is warmer than
another, the first object will radiate its heat to the cooler object.
You can perform a demonstration of this phenomena yourself by simply
holding the palm of your hand a few inches away from a cold window. What
you perceive as cold "draft" coming from the window is actually your
body losing heat to the window by radiation.
What this means is
that a floor which is a few degrees warmer than the ceilings, walls,
furniture and people will radiate its heat into the room at a constant
comfortable rate without the help of noisy moving air or bulky baseboard
heaters. There are virtually no cold drafts or hot ceilings and
furniture can be placed anywhere.
IS RADIANT FLOOR HEATING
NEW, AND WHY HAVEN'T I HEARD OF IT BEFORE?
You have probably
heard the saying that, "there is nothing new under the sun." Well, that
is certainly true of radiant floor heating. History records many uses of
this most comfortable form of heating around the world.
the days of the Roman Empire, a sophisticated system of fires were built
under the great stone floors of their bath houses. This kept the floors
and the rooms warm so the patrons could lounge in luxury beside the
The Koreans have done the same for thousands of years with
their homes. They have a fire pit under one end of the house and direct
the heated air and smoke under the floor of the house and up a chimney
on the other side. Great stones placed under the house in the path of
the heated air retain the heat and continue to keep the floor warm
throughout the night after the fire has gone out.
used hot water piping in the floor for many years. After World War II,
GIs brought the idea to the United States and thousands of copper and
steel pipe systems embedded in concrete slabs were installed. Many are
still operating today and their owners would not trade radiant floor
heating for any other kind.
The expense and limitations of those
early U.S. systems contributed to the waning interest in radiant floors
in the mid-sixties. Although radiant floor systems have continued to be
used over the years on a limited basis, it was not until the advent of
synthetic rubber and plastic tubing suitable for the job that there
began a renewed interest in radiant floor heating.
interest was rekindled in the late seventies and early eighties, a new
industry has grown up around radiant floor heating. People are
rediscovering the extreme comfort and energy efficiency of this type of
The cost effectiveness of new technologies and construction
techniques has made the comfort of radiant heating affordable and
adaptable to almost any situation.
HOW EXPENSIVE IS RADIANT
As with any heating system, the answer to this
question is relative to the application. In a warehouse application or
other concrete slab applications it can be very competitive with other
more common forms of heating.
When used in concrete slab housing,
radiant floor heating can be a very economical way to go. The cost of
these applications depend on the extent of control and complexity of the
installation. When used in multilevel residential applications, radiant
floor heat is generally more expensive than forced air to install. In
fact it could be up to two or three times the price of a forced air
system, depending on the application. Notice the word used is "price,"
not "cost." In the long run the forced air system will cost more because
a radiant floor system will generally use 15% to 30% less energy than
more common heating systems. Some systems in certain applications can
operate at only half the energy of their forced air counterparts.
Although cost is obviously an important question, it must be
remembered that you are buying comfort. You certainly would not buy an
economy car if you wanted luxury car comfort. Why invest your hard
earned money in selecting just the right house plan, cabinets, plumbing
fixtures, carpeting, etc., and then be uncomfortable six months out of
the year because of a heating system which creates drafts, blows dust
around, and whistles every time it comes on?
heating can be very effective in multi-story commercial buildings.
Generally speaking, the larger the scale, the more cost competitive it
becomes. Once again the actual cost varies with the complexity of the
installation and the application.
HOW ARE THE FLOORS HEATED?
There are several methods of heating the floor. Hot air can be
blown through floor cavities or pipes under the floor. Electric heating
cable can be embedded in or below the floor and is effective when the
energy source of choice is electricity. But, by far, the most prevalent
is the use of warm water flowing through piping or tubing in the floor.
Piping and tubing comes in all shapes, sizes, materials and colors.
The primary materials are copper, synthetic rubber such as EPDM and
plastics such as polyethylene, polypropylene and polybutylene. Synthetic
rubbers come with and without reinforcement, polyethylene come
crosslinked and un-crosslinked and they all can be made with or without
an oxygen diffusion barrier.
As with any industry, each
manufacturer has a list of valuable features associated with their
product. To a consumer all of these choices can become confusing,
particularly when listening to salespeople explaining why their tubing
is superior to the others. The fact is, the majority of products on the
market today will do the job nicely. The key is proper design and
application of the total system.
Each manufacturer has provisions
for use of their products in radiant floor heating systems and as long
as they are installed according to the manufacturer's specification, you
can be assured of many years of comfortable heat.
WHAT KIND OF
HEAT SOURCE CAN I USE?
One of the real benefits of radiant
floor heating is its flexibility. What is required is warm water,
generally ranging from 90 to 140 degrees F.
The most common
source of hot water is provided by a boiler. These come in a variety of
sizes and shapes and cost. They can be fueled by natural gas, propane,
fuel oil, wood, coal, or other combustible fuel or electricity. The
choice is made based on the fuel available and the economics of the
Alternative energy sources such as solar and
geothermal are also a very good match for radiant floor heating. Radiant
floors use relatively low water temperatures which makes very efficient
use of these type of heat sources.
The ultimate selection of the
heat source is usually left up to the engineer or installer on the job.
Unless the customer makes a specific request, the installer will
probably choose his favorite product or at best give the customer a
choice of several. The important factors in choosing a heat source are
the fuel used, energy efficiency of the unit, serviceability and cost.
Highly efficient units generally cost significantly more than moderately
efficient units. The choice becomes one of investing money at the time
of installation and paying higher utility bills.
advantage of radiant floor heating is that no matter which boiler you
choose, in all probability it will consume less energy than if it were
connected to any other type of heating system.
WHAT ABOUT AIR
Air conditioning and heating are distinctly
different and opposing functions. An effort to combine both systems into
one can lead to compromises which limit the effectiveness of either
system or both. Warm air rises and cool air falls, therefore it is only
logical that the heat should be in the floor and the cooling in the
With a central cooling system, independent of the
heating system, ducts can be routed through the attic to serve rooms
from inside walls. This technique reduces installation costs and
eliminates unsightly ducts in the basement ceiling.
conditioners and the new ductless split systems which are rapidly
gaining popularity, are a good alternative to central cooling. They
allow cooling to be directed to specific areas of the building thereby
saving energy and spent on utility bills.
With the growing
concern for indoor air quality, the old centralized combined heating and
cooling system may become a thing of the past.
WHAT HAPPENS IF
A LEAK OCCURS IN THE FLOOR?
This is an understandable concern
for the consumer. It is surprising that the same question isn't asked
when the domestic plumbing is embedded in the walls, floors and ceilings
of a building. We all assume, generally from experience, that the
chances of the water pipes in the wall springing a leak are relatively
small. If we didn't feel it was a good risk we would have all plumbing
pipes run on the outside of the wall.
Experience tells us that
the chance of a pipe failure in the floor is also very small. The
Uniform Mechanical Code requires that the pipe or tube must be a
continuous length while embedded. That means that there are no joints in
the floor. The pipe is usually encased in cement or some other type of
cementitous product so it is well protected. A leak is only likely to
occur if a nail or some other object is driven down through the pipe or
if there is severe cracking and shifting in the concrete. The quality of
piping and tubing products today insure a long life and are as reliable
as the pipes in your walls.
One other point of interest: unlike
domestic water systems which will spew forth an unlimited amount of
water if a leak ever does occur, radiant floor heating systems are
generally closed loop. That means that there is a limited amount of
water which continues to recirculate through the system over and over
again. Most residential systems hold only a few gallons of water. An
unlikely leak would spill only a few gallons at worst into the building.
An exception would be in the case where an automatic fill valve (outside
makeup water) was left open.
HOW WARM DO THE FLOORS GET?
The temperature of the floor, in most cases, is governed by the
outdoor temperature and the rate at which heat is lost from the room. If
you wanted to maintain a room temperature of 70 degrees F, the floor
surface temperature may range from 72 degrees F on a mild day to 85
degrees F on a cold day. Generally speaking, the colder it gets outside,
the warmer the floor becomes.
The floors should never feel hot.
On a day when very little heat is needed, the floor will feel neither
cold nor warm, just neutral. On cold days, the floor and the house will
feel cozier the colder it gets outside. Without cold tile floors, you
can put the slippers away in the dead of winter. On the other hand, the
floor is never so warm as to make wearing shoes uncomfortable. It is
always at a mild temperature so it works equally well in warehouses,
factories, offices or homes.
WHAT KIND OF FLOOR COVERINGS CAN
Radiant floors are regularly used with all kinds of
floor coverings. One thing to keep in mind is that whatever you cover
the floor with, the heat must penetrate it to get to the room. This
makes bare concrete, tile, linoleum or wood some of the best choices.
The result is beautiful floors that are both desirable and durable
but in the past were cold and uncomfortable.
Carpet may also be
used when the proper guidelines are applied. Lower nap plush carpets are
preferred. Generally speaking, the deeper the carpet, the more it
inhibits the heat flow from the floor. Carpet pad is a major deterrent
to proper operation of a radiant floor. Thick urethane pads are the
poorest choice for carpet cushion because they were designed to
insulate. Carpet manufacturers are now departing from the thick pad and
turning to the thinner, denser pads for longer carpet life and better
feel. These thinner, denser pads work much better with radiant floor
Millions of square feet of carpeted areas are
successfully being heated by radiant floors, The manufacturer and/or
installer of your system can help you select the best floor covering for
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