Estimate your peak-hour demand for hot water. This figure will be the maximum amount of hot water needed in a one-hour period. Estimate the water usage for various elements in your house -- dishwasher, washing machine, showers, baths, ice maker and any other appliances.
Many houses use heat pumps to heat their water. A heat pump will force the transfer of heat from cooler areas to warmer areas. In a lot of cases, the same unit can perform double duty as an air conditioning unit and a water heater. Interior heat pumps have the capability to circulate heat throughout the space of a house and heat your stored water supply, thus reducing your energy bills significantly during the summer months.
Find the heat pump's first hour rating, or FHR, on any heaters you are considering for purchase. The first hour rating is the amount of hot water in gallons the heater can supply per hour, starting with a tank full of hot water. Based on your previous calculation, you will know how much heat would need to be reclaimed to fully heat the tank or to meet your desired needs.
Connect the condensing unit to your selected heat pump. Refrigerant vapor exits the compressor at a temperature in the range of 120 to 140 degrees. The distance from the condensing unit to your water tank will affect the temperature drop from the time it leaves the condenser to the time it arrives at the water tank.
Connect the heat pump to your water tank. The heat pump will force the heated air into the tank to begin heating the water to the desired temperature. While it will not be at the 140-degree level it was at when leaving the condenser, it should still be high enough to heat the water to the appropriate level. The heat pump will also force the refrigerant vapor to return to the condenser system to continue cycling.
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