Heat pump or straight-cool AC for a South Florida home

What the two systems actually are

A straight-cool system is an air conditioner: it moves heat out of the house. On the rare cold night, electric resistance strips in the air handler provide heat. They are simple and cheap to buy, but they use a lot of electricity for the heat they make.

A heat pump is the same air conditioner with a reversing valve that lets it move heat into the house instead. In cooling mode, which is what it does most of the year here, it behaves exactly like a straight-cool unit. In heating mode it moves heat rather than making it, which uses far less electricity than strips. A small heat kit usually stays as backup.

Cost and efficiency

Up front, a heat pump costs a little more than a comparable straight-cool system. In summer the running cost is the same for the same efficiency rating. The savings come on cold nights, when the heat pump heats efficiently instead of running the strips. In South Florida there aren't many of those nights, so the savings are modest, but so is the price difference.

Every new system has to meet the SEER2 minimum for the Southeast. Going above the minimum, or choosing a two-stage or variable-speed unit, costs more but runs longer, quieter cycles that pull more moisture out of the air, which is often the bigger comfort gain in a humid house.

Sizing is the same either way

In a cooling climate, both systems should be sized for the cooling load, from a room-by-room calculation. Oversizing a heat pump to cover rare cold nights produces an oversized air conditioner that short cycles and leaves the house damp. The backup heat kit covers the few nights the heat pump alone can't.

What changes in the house

Day to day, very little. The indoor air handler, the duct and the thermostat look the same. The thermostat has to be set up for a heat pump so it controls the reversing valve and brings on the backup heat only when needed. On a cold night the air from the vents feels warm rather than hot, because a heat pump delivers a steadier, lower-temperature heat than strips. That is normal, and the house still warms up.

How to decide

If you're replacing the whole system and the price gap is small, the heat pump is usually the better long-term choice. If the home almost never uses heat, if you're replacing only the outdoor unit and the air handler isn't compatible, or if the budget is tight, a straight-cool system is still a reasonable choice. Ask for both prices on the same quote.