Energy Star funded a research that shows more than 50% of all heat pumps have problems with leaky ducts,

Low air-flow: There should be 400 to 500 cubic feet per minute (cfm) air-flow for ever ton of the pump’s air conditioning capacity. the pump’s efficiency deteriorates if the air-flow is much less than 350 cfm. Cleaning the evaporator coil and increasing the fan speed can sometimes help here, but modifications to the duct-work is often needed.

Incorrect refrigerant charges: This usually doesn’t occur in the packaged systems because they got charged in the factory, but the split-systems get charged in the field, which often results in too much or too little charge. The system should be checked for leaks every time it is serviced. The air-flow needs to be measured before the system is charged because that changes the amount of refrigerant the system needs. Too much or too little refrigerant reduces the heat pump’s performance and efficiency.

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This is a type of heat pump which utilizes outside air to heat or cool an interior space. They are more efficient than many heat pumps, but less efficient than ground-source heat pumps. However, they are cheaper to install than ground-source heat pumps, and have become widespread in recent years.

Air-source heat pumps work best in more moderate climates. Extended periods of below-freezing temperatures make the pump work too hard for it to be very efficient.

Most air-source heat pumps are split-systems: they have one copper coil indoors and one outdoors. The supply and return ducts are connected to a central fan also located indoors. Some air-source heat pumps are packaged systems. These usually have both coils and the fan outside with the air delivered through duct-work in the wall or roof.

Air-source heat pump efficiency is indicated by the HSPF (Heating System Performance Factor) and the SEER (Seasonal Energy Efficiency Ratio).

• HSPF is the rating for the system’s heating efficiency. The most efficient systems have an HSPF rating between 8 and 10.
• The SEER rates the pumps cooling efficiency. Usually the higher the SEER the more expensive the system. The most efficient pumps have a SEER between 14 and 18. This rating is more important than the HSPF in warmer climates.

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