Radiant Heating Frequently Asked Questions
What is a Radiant Panel?
How does Radiant Energy Work?
Where are the Radiant Panels Located?
What about Temperature and Radiant Energy?
How are Radiant Panels Heated?
How do I control my Radiant Heating System?
How are Radiant Panels constructed?
What is Thermal Mass?
Are there Energy Savings?
DEFINITION of Radiant Panel
The surface temperature of the panel must be controllable and not exceed 300°F to be a true radiant heating or cooling panel. (Most panels operate under 150°F; floors generally less than 85°F.) It is only a "radiant" panel if 50% or more of the heat is transferred by radiant energy.
More familiar terms are "radiant floor" or "radiant ceiling" heating, or "radiators". These should not be confused with hot water or electric baseboard heaters which produce only a small percent of radiant energy and primarily heat air.
How It Works
"What is radiant energy?"
If you hold your hand over a hot cup of coffee and feel the heat your logical conclusion is that heat rises. Logical maybe, but not correct! "Hot air" rises but "heat" can travel in all direction. That is why you can feel the heat of the cup when you place your hand to the side of it. The transfer of radiant energy is caused by a warm surface giving up its heat to a cooler surface.
When two surfaces have a temperature difference, both surfaces will attempt to equalize. Radiant energy will travel through space without heating the space itself only turning into heat when it contacts a cooler surface.
Our comfort relies just as much on radiant heat transfer as it does on air temperature, yet the majority of heating and cooling professionals think primarily in terms of air temperature.
As a result, we are missing out
on a truly comfortable living environment in our homes and places of
business. By controlling both the air temperature and the radiant transfer,
radiant panel systems bring a comfort that is unsurpassed.
Where are Radiant Panels Located?
For the most effective and efficient results, a radiant panel should be mounted on a sufficiently large enough flat surface. Lower surface temperatures are required on larger surfaces. A wall radiator could have a surface temperature of 180°F while an 81°F floor will do the same job.
When an object is "seen" by a radiant panel, it will heat its
surface. Therefore, it will heat all objects in the direct line
of sight from the panel; all ceilings, walls, floors, tables, chairs
or people. A heated ceiling will raise the surface temperature
of walls and floors, while heated floors will raise the temperature of
walls and ceilings. The air coming in contact with all these surfaces
will also be gently heated.
Radiant Energy and Temperature
At around 85°F, skin surface temperature is generally warmer than the surrounding surfaces. This makes us a radiant panel. If you stood by a large picture window in midwinter you would feel the heat leaving your body. We would feel comfortable if the rate at which we radiate heat is correct. When the temperature difference between the surrounding cool surfaces and our body becomes too great, we have to put on a sweater to slow down the rate at which we are radiating.
We receive heat instead when the sun beats down on us through the window and off comes the sweater. It is normal for us to lose heat at a constant and regulated rate. We are also designed to lose heat in many other ways. Air coming in contact with our skin conducts away heat. Evaporative cooling is caused by moving air in contact with our moist skin.
When heat is drawn away from our bodies at precisely the correct rate we have then attained a truly comfortable environment.
A heated floor normally "feels" neutral. Its surface temperature is usually less than our body temperature, although the overall sensation is one of comfort. Only on very cold days when the floor is called on for maximum output will it actually "feel" warm.
Heat coming from a wall radiator can be felt the closer you get to it because its surface is much warmer than your body. Radiant ceiling panels are also generally warmer than your body so you will feel some warmth on your head and shoulders.
YES! All these radiant systems
are designed to match the heat loss of the human body in a way not possible
by any other form of heating. Plus these radiant experiences are far
more pleasant than being hit by the hot-then-cool breezes which are often
associated with a forced-air furnace.
How Panels are Heated
The most economical way is through water.
It can be heated by almost any utility such as natural gas, propane,
oil, wood, solar, or electricity, and is quite versatile.
How to Control Your Radiant Heating System
It's simple! A wall thermostat is generally all that's required. Running
in the background may be a "weather sensitive control" which
will adjust the panel temperature based on the outdoor temperature for
increased comfort and economy. The radiant advantage is an option of
a thermostat in every room. Now you can turn down the temperature in
those rooms that are not in use or that you prefer to have cooler for
additional comfort as well as energy savings.
Construction of Your Radiant Panels
Panels come factory assembled or constructed on site. They can be surface mounted on floors, walls or ceilings or embedded. Wall and ceiling panels generally come pre-assembled and are primarily metal with a decorative surface. Floor panels are usually part of the floor construction. They consist of electric cable or warm water tubes embedded in or attached to the floor. The cable or tubes may be buried in a concrete slab, covered with concrete or gypsum on a wood subfloor, sandwiched between layers of a wood floor or attached beneath the subfloor.
Often metal
plates which act as fins to disperse the heat within the floor are
used in wood floor applications. Radiant panels can be used effectively
in combination with other forms of heat distribution including baseboard
convectors and forced-air. For example a home may have a heated concrete
floor on the lower level and forced-air on the upper level.
Thermal Mass
The ability of a material to retain heat refers to Thermal Mass. For example, a heated stone will remain warm much longer than a block of wood. This is because the stone is denser containing more mass. The mass of the earth can be used as a flywheel when it is heated under a radiant concrete slab. This storage of heat can carry a building through a time when energy is not available.
When "off-peak" electrical rates are offered, using a radiant floor in conjunction with the thermal storage of the earth beneath the slab can produce some very low electric bills.
When a big overhead door is opened, thermal mass in a heated shop or hangar floor responds rapidly to the change of air temperature. All the heat that has been "trickled" into the slab over time is released quickly to combat the cold air rolling in over the floor. This will happen because of the sudden and dramatic increase in temperature difference between the slab and the air. When the door is closes the building returns to its normal comfort setting almost immediately.
Providing an even surface temperature so some mass is required to spread the heat across the panel is the key to any radiant panel system. This mass may be in the form of a gypsum or other cementitious material or metal plates in the panel construction.
Some underfloor systems simply rely on air currents within the joist
space and the mass of the wood subfloor to spread the heat. When properly
designed, these systems are a good alternative for retrofitting an existing
building.
Response Time of Your Radiant System
Response time should be measured by the amount of time it takes to make the occupant "comfortable". -See Radiant Energy and Temperature- Often response time is referred to as the time it takes for the system to raise the room temperature when the thermostat setting is increased. Unfortunately, this is not an accurate definition of response time and can often lead to false conclusions that radiant systems can be slower than other heating systems. Radiant systems can have a faster response time than other forms of heating in some cases.
Wall and ceiling panels generally have far less mass than floor panels
and therefore respond quickly to changes in the room environment. This
is particularly true when recovering from setting back a thermostat at
night or when returning from vacation. Floor systems are very stable
and maintain a uniform climate because the floor surface remains at a
constant temperature.
Energy Savings
Saving money on your utility bill and increasing your comfort at the same time is a winning combination. Multiple zoning to allow unused rooms to be turned down plus use of thermal mass for off peak storage can reduce energy bills. Naturally choosing to lower your overall thermostat settings is another energy saver. You feel comfortable at room air temperatures which are lower when both air temperature and radiant transfer are compensated for. You will no longer have to force yourself to turn down the thermostat to save, you'll do it automatically to be comfortable.
How do we get heat loss? It's simply driven by the temperature difference between the inside and outside of a building or structure. Conventional systems locate registers along outside walls, under windows and in front of sliding glass doors to compensate for all those cold surfaces. That hot air goes up those cold outside walls, across the ceiling and down to the cold air return. In other words, all places where heat loss occurs. This is a great setup for wasting energy. Radiant panels direct the heat to the interior of the space and reduce or eliminate the excessive temperatures on outside walls and ceilings. This can result in energy savings of 10% to 30% in most residences and up to 60% or more in shops, hangars and warehouses.