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Water Heaters

indirectWaterHeater.jpgOil-fired water heaters can give you low-cost access to virtually unlimited amounts of hot water.

Homeowners with oil-fired water heaters have discovered they have low-cost access to virtually unlimited amounts of hot water. Oilheat's ability to produce a reliable, inexpensive supply of domestic hot water is one of its strongest features. Although an oil-fired water heater may cost a little more to install up front, its efficiency in heating water means extremely low operating costs over the life of the unit.

Oil-fired water heaters have high recovery rates, which means they can heat large amounts of water quickly. A water heater's recovery rate is the amount of water whose temperature the unit can raise by 100° in one hour. For example, if it can increase the temperature of 40 gallons of water by 100° in an hour, the unit has a 40-gallon recovery rate. Oil-fired water heaters have recovery rates as high as 120 gallons per hour.

Please contact an oil dealer to find out which water heating option is best for your home and family. The oil company can work with you to make sure the water heater you choose has a sufficient recovery rate for your needs. Two adults, for instance, may never need more than 30 gallons of hot water an hour, but a family of six may need 70 gallons. An oil dealer can help you with another choice too, because oil-fired water heating systems come in two categories: direct and indirect.


Direct-Fired Water Heaters

In a direct-fired water heater, the water is heated directly by the heat of the oil flame. You'll usually find a direct-fired water heater in a home with a warm air furnace. The oil is burned in a combustion chamber under the water storage tank, and hot flue gases heat the water in the tank.

Indirect-Fired Water Heaters

In an indirect-fired water heating system, the domestic water is heated by hot water from the boiler. In many oil-heated homes, you may find an indirect-fired system that is also tankless. A tankless, indirect-fired water heating system can work in conjunction with either a hot water boiler or a steam boiler. There are three variations: internal tankless coil, external tankless coil and tankless coil with storage tank.

Types of Indirect-Fired Water Heaters


  • Internal Tankless Coil: In this type of indirect tankless water heating system, the coil containing the domestic water supply is located in the water jacket of the boiler. One drawback to this design is the absence of hot water storage; another is the need to maintain the temperature of the boiler water at a high level, high enough to heat the domestic water as it passes through the coil.
  • External Tankless Coil: This indirect-fired water heater has a separate storage tank that contains an internal coil. The unit connects to the sides of the boiler. A newer version of the external tankless coil water heater is the plate heat exchanger. It contains a series of wafers or plates with internal porting; plates alternate between boiler water and domestic water.
  • Tankless Coil with Storage Tank (or Aqua Booster): This indirect water heating system was introduced to boost water heating capacity. After water has been heated by going through the indirect system's coil, it is stored in a vertical storage tank. The temperature of the hot water in the tank is usually maintained by means of a recirculating loop; it allows water to be reheated by going back to the coil, either by gravity or forced circulation.

Note: Some local codes require an anti-scald control, also called a tempering valve, for tankless coil indirect water heating units.

Boiler and Hot Water Heating Controls

  • Regardless of design, any water heating system that stores hot water should have a pressure relief valve; it's installed to protect the system from high pressure.
  • With tankless coil designs (where no water is stored in a tank), a pressure-only relief valve may be used; it protects the coil and piping from excessive pressure.
  • A vacuum relief valve vents the system if a vacuum occurs inside the tank.
  • A back flow preventer prevents boiler water from flowing into potable water systems.
  • A direct-fired water heater needs an aquastat to control operation and temperature; it also needs a primary control and heat detector for safe operation of the oil burner.
  • The new indirect-fired units typically have a triple aquastat, which controls high and low temperatures. This device communicates with the oil burner via a built-in cad cell relay.
  • The aquastat can also control zone valves and the circulator.
  • Because water inside a tankless coil can be extremely hot, all tankless coil systems should have an anti-scald device known as a tempering valve or mixing valve. When necessary, it automatically mixes in an appropriate amount of cold water to lower the temperature of the water to the chosen temperature setting.