A heat pump has dual personalities. It warms in the winter and cools in the summer. Or at least that's how it's supposed to work. If it doesn't, call a meeting of the Fix-It Club. Here's the agenda.

How Does It Work?

A heat pump cools a home by moving interior heat to the outside; it warms the home by moving exterior heat to the inside.

A heat pump is a heat exchanger that removes heat from indoor air to cool it and extracts heat from outside air and pumps it indoors to heat a home. It takes advantage of liquid's tendency to absorb heat as it expands.

A heat pump has an outdoor unit in which a fan moves air through a coil that absorbs heat. A compressor then superheats the vapor and sends it through refrigerant lines to a second coil in the interior distribution unit. A blower pushes return air through the coil, warming the air and forcing it into the ducts. Meanwhile, refrigerant travels back to the outdoor unit to begin another full cycle through the pump. An automatic reversing valve reverses these flows as needed to keep the home's interior comfortable.

What Can Go Wrong?

"Why is it cold [hot] in here?" Maybe the heat pump isn't working as it should. Common symptoms include: The pump may not run, the unit may short cycle, and the automatic defrost cycle may malfunction.

Fix-It Tip

Heat pumps work well down to about 15°F. Below that, most require a backup heating source, usually electric-resistance elements installed in the furnace, ducts, or the pump cabinet. That's why heat pumps aren't as popular (or as efficient) in colder climates.