HYDRONIC HEATING / RADIANT IN-FLOOR HEATING WHAT MAKES RADIANT HEAT DIFFERENT THAN FORCED AIR OR BASEBOARD HEATING? In order to understand the benefits of radiant floor heating, we must first realize the shortcomings of our existing systems. FORCED AIR 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. RADIANT FLOOR 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. The obvious 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. 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 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. During 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 pool. 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. Europeans have 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. Since the 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 heat. 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 FLOOR HEATING? 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? Radiant floor 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 situation. 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. The big 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 CONDITIONING? 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 ceiling. 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. Room air 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 I USE? 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 heating. 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 your application.