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NORA Oilheat Technicians Manual

Chapter 13 Heating Systems Domestic hot water systems fall into two major groups, direct and indirect. A direct system is one in which the water is heated directly by the heat from the flame. There is combustion gas on one side of a heat exchanger and domestic water on the other. With indirect systems we use boiler water to heat domestic water. There are two types of indirect systems: the storage system, where the water is heated and stored for later use in a tank, and the instantaneous or tankless system, where the water is heated as it is drawn to the fixtures. Direct fired hot water systems Direct fired hot water heaters use a tank, Figure 13-22: Typical Center Flue Water Heater Exhaust 13-18 Heating Systems which sits over a combustion chamber and is surrounded by insulation and an outer casing. An oilburner fires into the combustion chamber under the tank and the hot combustion gases heat the water in the tank. There are two designs of water heaters: the rear flue heater where the gases pass around the tank and vent out the back of the heater, as shown in Figure 13-21, and the center flue heater where the gases pass through a freeway in the center of the tank and vent off the top of the heater as shown in Figure 13-22. Oil-fired direct heaters are typically glass lined steel tanks that are constructed of steel and coated on the inside with a ceramic material. This coating helps protect the tank from rusting and corrosion. However, the ceramic material is not impervious to water and an anode or “sacrificial’’ rod made of magnesium is immersed into the tank water. This rod will break down and give itself up to protect the tank from the corrosive properties of the air and chemicals present in the water. These anode rods should be checked routinely and replaced when necessary. Indirect fired water heating Internal tankless coil Tankless coils are a copper coil attached to a steel, cast-iron or brass mounting plate. The coil is placed into the water and/or steam jacket of a steam or hot water boiler and the coil plate with a Figure 13-21: Typical Rear Flue Water Heater Exhaust Out Water In In Water Out Oilburner


NORA Oilheat Technicians Manual
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