A heat pump normally consists of two parts: An outdoor unit and an
Indoor unit. A heat pump is comparible to a reversible window unit.
When you need cooling, it would work normally, it blows cold air inside
and hot air outside. If you took it out of of the window and turned it
around, then put it back in the window, it would blow hot air inside
and cold air outside. The only problem would be the controls are now
outside. A heat pump does that with electric controls to reverse the
functions of the coils. So it can heat or cool, depending on how you
set the thermostat.

Heat pumps can come in split systems, where one unit is outdoors and
the other unit is indoors. The indoor unit can be in a closet, the
basement, a crawlspace or the attic. The indoor unit connects to the
ducts. The outdoor and indoor units are connected to each other with
Freon lines and control wiring.

Heat pumps can also come in a packaged system, where everything is in
one box that connects to the house through ducts.

Heat pumps can also come in a PTHP, which is a motel type unit. PTHP
stands for Packaged Terminal Heat Pump.

Finally, there is a Mini-Split model. There are two units that connect
with pipes, but no ducts. The indoor unit looks like a very quiet
window unit with just a coil and fan and the controls. The compressor
and outdoor fan is in the outdoor unit.

The heat pumps are rated in Tons, SEER and HSPF.
Tons are the amount of cooling. It is 12,000 BTUs per Hour. It is like
Horsepower in a car. SEER stands for Seasonal Energy Efficiency
Ratio. It is cooling efficiency. It is like Miles Per Gallon in a
car. HSPF is Heating Efficiency and means Heating Seasonal Performance
Factor. Both SEER and HSPF are rated in BTUs per Watt. The higher the
SEER and HSPF, the better for your power bill.

The heat pumps are sold as a matched set, so both parts should be
installed together. Otherwise it would be like having a Ford car with
a Kia engine, Chevy transmission and Dodge rear end. It may run but
performance is not what you want and fuel economy is probably poor

a 10 SEER unit will only give you 10 SEER if it is matched to a correct
indoor unit. If it is connected to your old indoor unit, it will be
less efficient, perhaps a lot less.

Stretch