A heat pump's performance and energy efficiency not only depend on the selection and planning of the equipment but also on careful installation.

Consumers and home builders alike tend to accept the lowest bid for heating and air-conditioning work. This unfortunate choice can often leave a system lacking 10 to 30 percent in the materials and labor necessary to optimize heat-pump performance. Rather than just accepting the lowest bid, it's best to research the performance records of local contractors, and get involved in the planning and decision-making about your new heat pump system.

You can avoid most of the common comfort and performance problems from improper installation by following these guidelines:

• Make your home as energy-efficient as you can with proper insulation, energy-efficient windows, and an effective air barrier, etc. Then your contractor can install a smaller pump system with shorter duct lengths. In an energy-efficient home, it isn't necessary to run ducts all the way out to exterior walls to install registers near the exterior walls.
• Install the ducts inside your home's insulation and air barrier, if possible. Research shows that this strategy is a major energy saver.
• Insulate your ducts to R-8 if they must be located in an attic or crawl space beyond the home's air barrier and insulation.
• Locate the outdoor unit on the north side of your home if possible. If not, pick a shady spot. There should be no obstructions within 10 feet of the sides with openings and the top.
• Specify that the measured air leakage through your new ducts be less than 10 percent of your system's airflow. Air leakage of 5 percent or less is possible with careful workmanship.
• Tell your contractor that you want a return register in every room.
• Don't use building cavities as ducts. Building-cavity return ducts are notoriously leaky and often cause comfort, energy, and moisture problems.
• Pull on ductwork after installation to make sure it is fastened and sealed well. (Seal duct joints with mastic.)

http://www.eren.doe.gov/erec/factsheets/airheatpump.html