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System Performance Questions
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How long will my radiant heating system last?
A radiant heating system in a broader perspective is composed of various materials from different manufactures performing different functions. A radiant heating system is not a prefabricated purchase which will, once unwrapped, provide heat for your home. Instead it is a combination of parts and components – all chosen individually by your installer. To better answer the question, we need to look at three main sub-systems. One is the distribution tubing system. The second is the hydronic boiler or heat source. The third is the boiler safety and support equipment. The distribution tubing system if designed and installed properly will last the life of the structure and then some. There should be no reason why a piping system shouldn't be able to last a hundred years or more if composed of the right materials, namely copper. And, in today's controversial market of products and guarantees, actions and results are stronger than words. For our results, we have seen thousands of copper radiant panel tubing systems which have been in service for over fifty years with absolutely no signs of wear and tear, and looking as good as the day they were installed. We are describing on-site physical inspections of these in-slab systems. We do recognize, for the sake of the argument, there have been some problems as with all things man made with copper radiant panels in certain circumstances. These problems, rare as they exist, are inherent to poor construction and installation and not the materials. Other piping materials such as the plastics, rubbers, and steel tubing have had problems with the material itself within much shorter periods of time. To answer the question of longevity concerning a tubing system completely depends on the type of tubing you use and how it is installed. Our representation for tubing choice defaults to the best overall proven performer for radiant heating with our ideal installation. Every time one of these manufactured tubing products fails, another is produced promising superior performance to its successor – until it to fails to deliver. Some manufacturers are claiming new plastic and rubber piping have a service life in excess of 100-300 years under normal use. It sure sounds great when it is being covered with concrete, until a few years down the line where problems can and do develop causing damage to your system and home. There are over 15 different types of plastic and rubber tubing made for radiant panel heating. Some better than others. Some costing more than others. Some trying their hardest to provide better performance than copper but can't. Our intentions are to hold our references to the highest standards, to create the base at which we consider all others. Rather than the promises of a salesman, we go with what works, what has been a proven standard longer than any other material – copper – for the best radiant panel choice.
The typical hydronic boiler system will have a lifespan of 30-45 years or more. Of course maintenance and monitoring are key factors to ensuring the proper lifespan of these units. We have seen premature failures as early as a couple of years if a system is running improperly or without adequate water pressure. We have also seen boilers that are over 80 years old which are still in service and operating fine. Overall, our average lifespan has been determined from the replacements we have made while servicing the tens of thousands of radiant heated homes in our service area which are 30-60 years old. The average age of these replaced boilers far exceeds the average age of forced-air furnace replacements.
The systems safety and support equipment can have life-spans ranging from 5-30 years or more with the average age for certain parts varying depending on the system function. As always the maintenance and inspection of these parts on a regular basis greatly increases the chances of them having a longer lifespan. Equipment containing more electronics or moving parts certainly move ahead on the aging scale. Electronic ignition modules, which allow a boiler to use an intermittent pilot for the heating cycle instead of a constant standing pilot, and zone valves, which open and close every time a thermostat calls for heat, tend to wear out more often (5-15 years) than parts which are not dependent on constant function like gauges and flow switches. Different series of equipment are built to different standards. Unfortunately some are built to fail after a certain operating time. Other equipment like circulating pumps and gas valves are built better and last longer. Overall, safety and support equipment lasts on the average between 20-30 years.
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I hear radiant heating systems are slow to react, the so-called “lag-period” and also tend to overheat. Is system design a factor in these cases?
The design of a radiant heating system along with other factors influence the response of the system. A properly designed system with specialized controls will substantially reduce or eliminate lag-periods and overheating. However, other factors can influence these processes and include the amount of insulation, exposure to sunlight, rapid climate changes, concrete slab thickness, boiler safety and support equipment and size, and owner operational preferences. Two common complaints about the performance of older radiant panel systems is the lag-time, the time it takes to change the room temperature once the thermostat calls for heat, and overheating, the rapid increase of room temperature due to the influx of solar energy (insolation) or the influx of body heat (a sudden increase in room occupancy). The lag time is a system response due to boiler output and the concrete mass to be heated. For example, a 6” concrete slab-on-grade will take longer to heat than a 1-1/2” slab on a wood sub-floor. However, once the slab is heated, slabs with more mass will maintain the temperature longer and prevent hysteresis (rapid cycling of the boiler equipment). For these reasons, we suggest during the heating season you leave the thermostat set 24 hours at one specific comfortable level for homes with slab-on-grade construction containing thicker slabs. There is much data to confirm you will save 15%-19% on your heating costs if you follow this suggestion. For thinner slabs, 1-1/2” to 2”, better efficiency, reduced operational costs and comfort gains can be obtained with auto-setback thermostats that vary both the time of operation and temperature of the conditioned space.
For older homes, inadequate tubing amounts and spacing can cause increased system response times as well. This is simply a function of providing calculated BTU energy into the conditioned space from a source. Less tubing reduces BTU transfer and improper layout can direct the warmest water to incorrect areas of the home. These important issues are critical and need to be considered by the design engineer.
Overheating is a result of boiler control and outside climate changes. If the water is circulated too hot through the slab, too much energy can be stored within the concrete mass. Once the thermostat setting is satisfied, the slab will continue to radiate its stored energy. Rapid insolation or infiltration of solar energy from the sun into the heated space can play a big factor in system overheating. Cool mornings that quickly turn into hot afternoons can catch the thermostat by surprise. The system heating cycle operates all morning storing energy in the slab only to continue to radiate the energy once the thermostat turns off while the outdoor temperature continues to rise. No wonder the conditioned space overheats. Concrete slabs with more mass tend to have this problem more than thinner slabs. Additional control devices can help the system compensate for such climate changes such as outdoor temperature overrides, outdoor temperature resets, thermostatic controls, and aqua-static control modules. Outdoor thermostats when placed in a shady area on the east facing side of a home and under the eave can override the effects of increased outdoor temperature by shutting the boiler system off at a particular set point. Also, advanced control systems can regulate the boiler water temperature according to outdoor climates. As the outdoor temperature rises, a sensor commands the boiler to reduce its water temperature and overheating can be minimized. Auto setback thermostats and proper boiler aqua-stat settings can usually provide sufficient control; however, the climate affecting the home and its orientation may call for more sophisticated controls for maximum comfort.
The amount of insulation contained in the structure can greatly affect both overheating and lag-time. If the house containing a radiant system is poorly insulated, then climate changes play a large part in the inside environment too; however, regardless of the outside factors affecting your home, there ia a system design which can control and provide a comfortable inside environment regardless of climate conditions.
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I have one or two areas of my home that don't heat. Why?
This question can be answered most directly by a qualified service technician after system inspection. Some possibilities to consider for poor system performance are as follows:
- Air-locks in the tubing system. Many homes built with radiant heat have a common supply in the concrete that tees to individual circuits for water distribution. If air becomes trapped in one circuit, some of the circuits containing solid water will properly circulate while bypassing those which are air-locked. A radiant panel needs the tubing to contain solid water for proper performance and heat transfer. The reasons for air entering the tubing system can depend on: 1) the type of embedded tubing. The plastic and rubber products can be oxygen permeable allowing air to diffuse through the tubing walls and into the system. Copper tubing does not have this problem. 2) The expansion tank which prevents the system pressure from increasing dramatically during system operation can release its air into the system. A plain steel tank, commonly found in older systems, can release air overtime due to inadequate system pressure and circulation. Modern expansion tanks have a pre-charged diaphragm. If the diaphragm develops a hole, its air can be released into the system. 3) Automatic air vents which are common boiler support equipment items contain an internal float to allow the release of trapped air. If they malfunction when pressure decreases at the air vent, air can be sucked in by action of the system pump. 4) The most common reason for excessive air is a concealed leak in the embedded tubing. As the water is dissipated by the leak, the automatic fill system for the boiler will make up the lost water for safety. The city make-up water contains copious amounts of air and can quickly air lock any radiant panel system.
- Malfunctioning zone valve or manifold controls. If your house has multiple zones of control, the area not heating may contain a malfunctioning zone valve or thermostat. Usually the purpose of the thermostat is to activate the zone control valve. The zone control valve then signals the boiler pump and gas valve to operate. If either item fails, the flow of water is disrupted to the area and heating is prevented. It is more common for the zone valve to fail than a thermostat, pump, or boiler gas valve. Whether or not you have multiple automatic zones of control, the system will contain a return manifold that has balance valves. The manifold is typically located in a closet, inside room, or at the boiler. Some of the balance valves may be obstructed, shut off or balanced down thus preventing flow to the circuits. Balance valves should be in the fully open position for normal heating.
- The original system design may play a part in poor heating if the area in question has never heated properly. Uneven circuit lengths, insufficient tubing, improper tubing depths, and poor circuit layout can all affect individual areas. This holds especially true for homes which have large areas of varying heat loss and solar input. The original design should be reviewed to clarify the possibilities.
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I know of radiant floor systems that are as new as 5 years old that don't work. Why?
We would surmise either the system never worked properly from the start, was installed poorly, or has experienced premature failure of one or more support equipment items. Many components work together to make a radiant system work. A failure of one or more of these components could contribute to poor performance. A professionally installed radiant panel system is regarded as being very reliable with low maintenance to operate. A five year old system should be considered brand new in respect to overall system life. The question is – How long has the system not worked, from the start or 5 years later? We usually will rely on historical data to form initial opinions about the system. Since a relatively new system has less history, it is more difficult to arrive at an immediate conclusion about the problem. First, realize that there isn't a component made that is not susceptible to failure. It is possible for a new system which is installed well to fail because of one bad component or improper adjustment. A safety switch could have tripped and needs resetting, an ignition module may have burned out preventing boiler ignition, a valve may be turned to the wrong position, or an electrical fuse could have blown. If it is a simple problem, it should be examined, fixed, and not used to establish a performance opinion of the system as a whole. Now on the other hand, if it is poor materials, design, or the installation that is suspected of causing the problem, we would suggest receiving an alternative opinion before proceeding with any repairs. As a homeowner the initial things to check are: 1) the system pressure; it should be 10-25 psi always. 2) The electrical power to the system; it should have power. 3) Its sound; it should not be making any unusual noises during operation. If these initial criteria are met, then a more in-depth examination is needed.
Our final advice would be to have the system inspected by a qualified serviceperson before forming too many opinions. There are both very minor or large problems that can affect safe and efficient system operation.
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ANDERSON RADIANT HEATING
520 East McGlincy Lane, Suite 16
Campbell, CA 95008
Phone: (408) 378-3868
Fax: (408) 559-0818
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