Call for Space Heating Only Operation
When the thermostat calls for heat, the circulation pump is activated and hot water is drawn from the top of the water heater through the air handler, and then returned to the water heater. There should be at least a 20˚F (11˚C) temperature drop between the hot water supplied to the air handler and the returning water temperature. If the temperature drop is less then 20˚F (11˚C) two things may happen:
1.Mixing of warm return water with the hot water within the water heater (no tank stratification), which will result in a lower hot water supply temperature.
2.A water heater thermostat temperature differential (between on and off) is approximately 18˚F (10˚C). Therefore, if the return water is not cool enough, it may not activate the water heater thermostat, which causes the burner to operate. All of the water in the water heater will be cooled before the burner begins to operate. This may cause large swings in the delivered hot water temperature, causing poor space heating performance, fluctuating domestic water temperatures and effectively reducing the supply of domestic hot water.
Call for Domestic Hot Water and Space Heating Operation
When both return water from the space heating loop and new cold water (replacing domestic water being used) enters the water heater, the mixed entering water is cool enough to activate the thermostat quickly. In this situation, the water heater must be capable of satisfying the combined need for hot water (domestic hot water and space heating) at the same time.
Air System
A circulation fan draws cool house air at approx. 70˚F (21˚C) from the return ductwork, forces it through the water coil where it is heated, and then distributes it to the various rooms of the house through the supply ductwork.
Water Piping
The Piping and fittings used to connect the water heater and air handler must be sized to handle the volume of hot water required by the air handler within the pressure limitations of the circulation pump. All piping, fittings solders, and fluxes must be acceptable for use with domestic hot water.
Note: Chemicals (such as boiler system additives) cannot be added to the system because water passing through the heating loop
Circulation Pump
The circulation pump is factory installed within the air handler. The water flow rate will vary depending on the pumps performance and the head pressure (resistance) of the complete heating loop system.
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