How Hydronic Heating Works

A quiet revolution in home heating is sweeping America. More and more, homeowners are turning to what many consider the most comfortable heating solution, hydronic heating, which utilizes water instead of or in addition to air as the heat transfer medium. Homeowners are learning from their co-workers, friends, neighbors, and relatives that today’s hydronic heat is draft-free, quiet, clean, efficient and, above all, comfortable.
Hydronic heating works by using the efficient transfer of heat through water. Since water conducts heat more easily than air, less energy is used to spread heat throughout the house.

A heat source such as a boiler transfers heat through pipes that are connected to wall panels or placed underneath your floor. These pipes transfer heat to the walls or floor of a room, which then radiates heat waves throughout your house. As a source of radiant heat, a hydronic system warms the surfaces it touches much like the sun’s rays. The surface then becomes a radiator, extending the heat in every direction and creating clean, even and comfortable warmth.

Hydronic heating systems circulate hot water through plastic tubing, baseboards, or radiators to provide gentle, silent, and clean heat. Many homeowners live with rooms that are too hot or too cold. To maximize comfort, each room in a hydronically-heated home can be zoned separately allowing each room or area to be controlled individually. Furthermore, hydronic heating systems are extremely efficient because of design advances in boilers, zoned heating, and the nature of the heating system.

Although Americans have used hot water and steam boilers for decades, recent technological advances in boilers and heat distribution systems have spurred an increased demand for hydronic installations. For example, the advent of extremely durable plastic tubing has made it possible to hydronically heat floors, walls, sidewalks, driveways, and swimming pools. Plastic tubing is flexible, so it is easy to install and service, making it more economical to use than other types of piping materials.

Benefits of Radiant Floor Heat

CLEAN – Radiant heating does not blow dirt, dust, bacteria, viruses and pet dander around the house all winter long.

COMFORTABLE – The sensation of comfort is caused by a combination of air temperature and radiant energy that equals the body’s energy needs. When you receive a greater amount of radiant energy, you will be equally comfortable at a lower air temperature.

EFFICIENT – It’s like being out in the sunshine. You are more comfortable at a lower air temperature. This lower air temperature will save you money on your energy bills.

ECONOMICAL – Studies conducted by the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) indicate that with radiant heating systems people can be comfortable at temperatures 6°F to 8°F lower than with hot air systems. Energy experts calculate that you can easily save 25% of your heating costs with a radiant heating system

HEALTHFUL – Unlike hot air systems, radiant heat will not dry out your breathing passages and leave them more vulnerable to infection.

Radiant-floor heating offers a number of significant benefits:

By far, the biggest selling point for radiant-floor heating is comfort. The large radiant surface means that most of the heat will be delivered by radiation-heating occupants directly-rather than by convection (the primary mechanism of heat delivery from conventional hydronic baseboard “radiators”). Warmer surfaces in a living space result in a higher mean radiant temperature, a measure of surface temperatures in a space that influences the rate of radiant heat loss from occupants). With higher mean radiant temperatures, most people are comfortable even at lower air temperatures. Delivery of the heat at floor level with a warm floor surface also allows occupants to walk around barefoot even in winter-a very popular feature. Enhanced comfort should be a big selling point in any green home, so a strong case can be made for this heating approach.

“Until you’re lived with this form of heat,” says Radiant Panel Association executive director Larry Drake (who got involved with radiant heating after years of working with solar houses), “it’s hard to understand how comfortable it is.” He argues that with green homes in particular, after going to all the effort and expense to incorporate healthy and sustainable materials, ensuring high levels of comfort with radiant heat should be a top priority.

Forced Air vs Radiant HeatingEnergy Savings
There is potential for saving energy with radiant-floor heating through several mechanisms, including lower thermostat settings, lower-temperature boiler settings, and reduced infiltration. Homeowners with radiant-floor heating are likely to be comfortable at lower air temperatures because of the elevated mean radiant temperature in such homes, the lack of significant airflow (as occurs with convective hydronic heating and forced-air heating systems), and the delivery of heat at floor level. Proponents of radiant-floor heating argue that someone normally comfortable at 72°F (22°C) will be comfortable in a building with radiant-floor heating kept at 68°F (20°C). If this is true, one would expect people with radiant-floor heating to keep their thermostats lower and thus realize significant energy savings.

The second opportunity for energy savings with radiant-floor heating is through keeping the boiler temperature lower than is necessary with conventional baseboard hot water distribution. The typical European approach with radiant-floor heating is to circulate fairly low-temperature water on an almost-continuous basis, varying the water temperature as needed to satisfy the load. This practice might reduce heat loss into unconditioned space if boiler and piping are located in an unheated basement, but experts EBN spoke with suggest that the savings would be very small at best-especially because of the additional electricity consumption to operate pumps for long hours.

Green building consultant Marc Rosenbaum, P.E., of Meriden, New Hampshire, suggests using a low-mass boiler that is fired on-demand, rather than a high-mass boiler operated almost continuously.

The third opportunity for energy savings (over forced-air heat) is that radiant-floor systems do not increase the rate of air infiltration. Standard forced-air heating systems can significantly increase or decrease air pressure in different parts of a building, which in turn can increase air infiltration/exfiltration rates-at least in a conventional, leaky building. With radiant-floor heating, as with baseboard hydronic heating, this will not happen. (A well-designed, properly balanced forced-air system should not increase infiltration.)

Potential for use of solar energy. The relatively low temperature required for circulation water in a radiant-floor heating system provides an opportunity to utilize solar hot water. This approach works best with concrete-slab systems; higher-temperature water is generally required when the tubing is attached to the underside of wooden floors. While such systems are fairly complex and expensive, radiant slabs offer one of the best ways to make use of solar energy for heating portions of a building without direct access to sunlight. Most practical are systems in which solar energy heats water in a storage tank that can then be circulated through the slab. According to an EREN Consumer Energy Information Brief ( titled “Solar Radiant Floor Heating,” such systems typically cost at least $14,000. Backup heat is still required and can be provided with a wood stove, through-the-wall-vented gas heater, electric resistance heat, or backup heating element in the solar storage tank.

Increased Boiler Life
By operating a boiler at a lower temperature, its life can be extended. Radiant-floor heating systems typically use water temperatures of 85-140°F (30-60°C), compared with baseboard hydronic systems that typically operate at 130-160°F (55-70°C). At these operating temperatures, boiler life can exceed 45 years, according to information from DOE. (Shapiro is skeptical of this claim, however, pointing out that newer boilers are made for cold-start operation and should hold up well with this temperature cycling.)

Quiet operation
Radiant hydronic floor heating is extremely quiet. Unlike forced-air heat, there is no noise from a fan or airflow through ducts; and unlike hydronic baseboard heat, there is usually no gurgle of water through baseboard radiators or creaking from expansion and contraction. The primary noise will be the sound of circulating pumps and the fan used in power-venting the boiler. With radiant-floor systems that have tubing attached to the underside of wood flooring, there may also be some creaking from expansion and contraction.

Flexible room layout
Because there are no baseboard radiators or air registers with radiant-floor heating, there is much greater freedom as to where furniture can be placed. Radiant-floor heating systems are “invisible.”

Improved indoor air quality
An argument can be made for improved indoor air quality in houses with radiant-floor heat. Compared with a conventional forced-air distribution system, there is likely to be less dust circulated around the house. And unlike electric baseboard or forced-air heat, there will be no surfaces hot enough to burn dust particles-which could introduce volatile chemicals or toxic particulates into house air (even passing through filters). This concern would be greatest for people with acute chemical sensitivities. In fact, veteran builder Max Strickland, of Burkholder Construction in Travers City, Michigan, first became interested in radiant-floor heating several years ago after his wife became chemically sensitive. He’s worried about “frying the air” with conventional heating systems and feels that conventional filters on forced-air systems are not effective. Strickland went on to build an American Lung Association (ALA) Health House in Travers City three years ago, and he now incorporates radiant-floor heating into all of his homes (typically 4 to 6 high-end custom houses per year).

Unsurpassed Heating Comfort. Your home will no longer have hot spots, cold spots, or drafts – just gentle, even, silent heat that automatically regulates itself to your desired comfort level. You won’t even notice that the heating system is operating, and that’s heating comfort at its best! Extremely Efficient Heat. Hydronic Heat gently heats the walls and furniture in the room, which delivers heat to you and your family and minimizes heat loss through the windows, doors, and ceiling. Furthermore, because Hydronic systems are sealed, there is virtually no loss of heat as it is distributed throughout your home. Easy Zone Control. Now you can “zone heat” every part of your house! Use individual zone controls or circulators and thermostats to automatically warm up the daytime living areas before you get out of bed and then let them cool down at night when you’re not using them. Turn down the heat in unused rooms for big energy savings, and don’t overheat a room when the sun is shining in! Trouble-Free Heating.

Finally, you can achieve the home comfort dream of a worry-free heating system. A Hydronic system has few moving parts so maintenance is minimized. Without a thought on your part, it will provide heating that’s so comfortable that you’ll never notice it. Healthy, Clean Heating. Hydronic Heat is gentle and draft-free, so it does not circulate dust, odors, spores, or germs around the house. Flexible, Expandable Heating. Your Hydronic system gives you total home comfort. Reliable, efficient space heating and domestic hot water. Swimming pool and spa heating. Ice and snow melting for your driveway and sidewalks. Even towel rack warming. That’s luxury! For comfort all year long, air conditioning can be added to your home in a separate system. Combine Hydronics and Warm Air Heating. There are even Hydronic Heating answers for homeowners wishing to convert or supplement their existing warm air or heat pump systems. Hydronic heating makes for great solutions for additions and retrofit projects.

Operates with All Heating Fuels. No matter which fuel you use to heat your home – natural gas, LP gas (propane), fuel oil, electricity, or even solar energy – Hydronic Heating is ideal for highly efficient, convenient, and draft-free comfort.