Radiant Heating Explained

A floor heated radiantly from below was an idea first used by the Romans and is today perhaps the most popular form of heating in England, and certain parts of Europe.

What is radiant heating? Outdoors, the air around us is primarily heated with the heated earth. For example, on a warm cloudy day, the air itself transfers the warmth we feel. On the other hand, a cold sunny day, the warmth comes from the radiant energy the sun. It's this form of heat that we feel in a home that is radiated from a warm floor.

How are floors heated? Hot water / hydronic radiant heating is by far the most common type in a home. Others types of radiant heating include, for example, ceiling radiant heating, radiators, and, baseboard heaters. Generally, hot water heating tubes are placed in the floor. The water is then heated with a boiler or domestic hot water heater that warms a floor. The result is a quiet, even and comfortable heat with no blasts of hot air to stir up dirt and dust. There are no radiators so furniture placement is easier and creates a safer environment with no surfaces that are too hot to the touch. Some studies suggest that with radiant heating systems people can be comfortable at temperatures 6°F to 8°F lower than forced air systems for example.

As radiant heat does not alter the air moisture content in homes, humidifiers typically aren't required like it is with forced air systems using combustion or by increased infiltration of cold, dry outside air. Often the air in a house is humid enough.

Air infiltration heat loss is reduced with radiant heat. When warm air from a furnace or baseboard heater (at a far higher temperature than radiant) flows against colder exterior walls, it draws cold air into the house through any cracks. With radiant systems, air is only warmed to the temperature of the thermostat setting, so the temperature differential at outside walls is less, reducing air infiltration.

With radiant heating, a warm floor heats the air that then rises to heat people is only partly true. Only a small percentage of the heat transferred to the room from a radiant floor actually comes from the heated air. The temperature of the air from the ceiling to the floor often never varies more than a degree or two.

Radiant 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've all probably all sat on a piece of furniture that sits by a window and is warmed by the sun. The warmed seat then makes you feel warm. What you perceive as warmth coming from the furniture is actually your body gaining heat from the window by radiation.

How costly is radiant floor heating? When used in a concrete slab for homes, radiant floor heating can be a very economical way to go. When used in multilevel residential applications, radiant floor heat is generally more expensive than forced air to install. Long term though, a radiant floor heating can use about 15% to 30% less energy than other more common heating systems. One must also factor in the added benefit that comfort can bring.

What heat source can I use? The most common source of hot water is that provided by a boiler. Commonly, boilers can be fuelled by natural gas, propane, fuel oil, wood or electricity. The choice is based largely on availability and cost. Other energy sources such as solar and geothermal are also a very good match for radiant floor heating since radiant floors use relatively low water temperatures.

What about air conditioning? Cooling and heating are clearly different. When the two systems are combined it can limit the benefits of either system or both. Some would that since warm air rises and cool air falls, it only makes sense that the heat should be in the floor and the cooling in the ceiling. So, an advantage of having an independent cooling system is that ducts can be routed through the ceiling area to serve rooms in the house. Room air conditioners also allow cool are to be directed to specific areas saving energy and money spent on whole house systems.

What about leaks in the flooring pipes? Like plumbing pipes concealed in wall cavities or ceilings we assume, generally from experience, that the chances of the pipes leaking is relatively small. Similarly, experience shows us that a pipe leak in the floor is small too. It's important to note that with pipes embedded in the concrete floor that the change of damaging them is small and it also assists with high pressure issues too. Since residential radiant floor heating systems are often "closed loop" systems there is a limited amount of water in the pipes themselves limiting the amount of water damage to the home.

How hot are the floors? Typically, the temperature outside and heat loss dictate floor temperatures in your home. Generally, the colder it gets outside, the warmer the floor becomes but the floors should never feel hot. On a mild day when very little heat is needed, the floor should feel neutral.

What floor coverings can be used? Radiant floors are regularly used with all kinds of floor coverings. Keep in mind though that whatever you choose, the heat must penetrate it to get to the room. This makes bare concrete, tile, vinyl sheeting, and, even wood good choices. Low nap carpets can work as well.

What about house ventilation? Air exchange is critical to any home. A ducting system does not have to be elaborate as long as the required air exchanges are provided e.g. moving the required about of cubic feet per minute. A HRV (heat recovery ventilator) or air exchanger that warms incoming cool air, for example, before it is supplied to living spaces is a good way of providing air exchanges and improving indoor air quality too.

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