Hot water heating systems, also called hydronic systems, use water heated in a water heater or boiler as the heating medium, which is then circulated through pipes to baseboard convectors or radiators.
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The Hot Water Heating System
There are two types of hot water heating systems, forced and gravity. According to the “Residential Rehabilitation Guide” by the Department of Housing and Urban Development (HUD) gravity systems, which are found in older single-family homes, have no water pump, require larger pumps and heat unevenly. For this reason, these units are usually replaced during a renovation. Forced water systems are usually heated by gas- or oil-fired boilers like their forced air counterparts, but use immersion-type electric resistance heating coils instead of burners in the boiling unit. Like electrically heated systems, gas- and oil-fired hot water heating systems use hot water pumps and distribution piping, with either one- or two-pipe or series-loop systems. Problems can arise in several areas of the hot water heating system, including the boiler, water heater or hydronic furnace; expansion tank; the boiler controls; distribution piping and radiators. Repairs should only be made by a certified technician.
Boilers and Water Heaters
Cast-iron or steel boilers used in hot water heating systems, according to “HVAC Fundamentals Volume 1,” by James E. Brumbaugh. Corrosion from water is a problem with boilers and can minimize their useful life. For this reason, cast-iron types, which have a greater resistance to corrosion, are used. Chemically treating the water will minimize this problem and extend the boiler's service life. Other boiler problems can include no heat from low water levels or thermostat or burner malfunctions. Brumbaugh recommends checking fuses, resetting breakers and replacing the batteries in programmable thermostats first before calling in a professional. Common problems with water heaters range from no hot water to insufficient hot water to slow hot water recovery.
Expansion tanks are installed near the boiler to allow expansion and contraction of the water as it changes temperature, according to Brumbaugh. Problems arise when the tank loses air and the unit becomes waterlogged, prohibiting expansion. Water is then discharged from the boiler's pressure relief valve, as evidenced by high pressure readings. In this case, a professional needs to be called in to drain and re-pressurize the expansion tank.
According to HUD, “all boilers should be equipped with a pressure gauge, a pressure relief valve and a pressure-reducing valve.” Other boiler controls include a high-temperature limit control as well as circulating pump and controls. Both low and high pressure can cause problems. If pressure readings are lower than 12 psi, this indicates a faulty valve that needs to be adjusted or replaced. In addition to causing waterlogged boilers, high-pressure may be caused by cracks in the coil of the water heater, according to HUD. Check for water near or below the valve. If a boiler gets too hot, an aquastat, a high-temperature limit control, should be installed, checked or replaced, as the case warrants. The circulating pump and controls sends hot water through the system at a constant flow rate. HUD recommends listening for loud operation in a pump which can indicate a faulty motor. Other problems include leaks in the seal between the motor and pump and faulty wiring if the pump is not operating correctly.
The hot water in a hot water heating system is transported by pipes, radiators and control valves. In distribution piping, valves and connections should be checked for leaks, and pipes should be insulated in unheated areas such as crawl spaces, attics and basements, according to HUD. If radiators are not warm during operation, there may be a problem with the system's zone control. Check the valves associated with the unit for leaks, faulty wiring or incomplete connections. Radiators should also be checked for leaks as well as an inspection of the unit's fins for dirt or damage, according to HUD. If the radiators do not warm up evenly, the air trapped inside needs to be discharged.
Disadvantages of Hot Water Heating Systems
Brumbaugh lists several disadvantages to hot water heating systems including high first cost, a lack of ventilation, slow heat response and the sometimes inconvenient placement of baseboard heaters. Home owners should take these issues under advisement when considering installing a hot water heating system. Again, repairs to equipment should only be performed by a certified technician.