Heat Pump FAQs: 12 Questions Answered

What is a heat pump?
How does a heat pump work?
How do you use a heat pump in winter?
How long should a heat pump run?
What size heat pump do I need for a 1500 square foot house?
How much does a heat pump cost?
What temperature does a heat pump stop working?
When should you switch from a heat pump to emergency heat?
How do I know if my heat pump has auxiliary heat?
How do I stop my heat pump from freezing up?
How much does it cost to run a heat pump?
How do I tell if I have a heat pump or a conventional AC system?

What is a heat pump?

A heat pump is an air conditioner that can also run in reverse to heat your home. It uses a refrigerant cycle to move heat rather than burn fuel or heat a coil. In summer it pulls heat out of the house and releases it outdoors, like a regular AC.

In winter a reversing valve flips the flow, and it pulls heat from the outdoor air and releases it indoors. Because it moves heat instead of making it, it can heat very efficiently. In the West Valley, where winters are mild, heat pumps are common for both new homes and replacements.

How does a heat pump work?

A heat pump works by circulating refrigerant between an outdoor coil and an indoor coil, with a compressor and a reversing valve controlling the direction. In cooling mode the indoor coil absorbs heat from the home and the outdoor coil releases it outside.

In heating mode the reversing valve switches, so the outdoor coil pulls heat from the outside air and the indoor coil releases it into your ductwork. Even cool air contains heat energy, which is why it works at lower temperatures. A defrost cycle occasionally melts frost off the outdoor coil. The thermostat tells the system which mode to use.

How do you use a heat pump in winter?

To use a heat pump in winter, set the thermostat to Heat, pick a steady temperature, and let the system hold it instead of making big changes. Heat pumps are most efficient in longer, gentler cycles, so large setbacks can push the system into backup heat.

The air from the vents will feel warm but not as hot as a gas furnace, which is normal. Keep the filter clean and the outdoor unit clear of leaves and debris. In the West Valley, winter use is light, so also check that the system switches over to heat before the first cold morning.

How long should a heat pump run?

A heat pump running long cycles on a cold morning is normal, especially in heating mode, because it delivers gentler heat than a furnace. It may run for much of the day while the weather is cold and still hold temperature.

Cycles that are very short, turning on and off every few minutes, can point to an oversized system, a failing part or a thermostat issue. Constant running that never reaches the setting can mean low refrigerant, a dirty coil, a duct leak or an undersized system. In summer, long runs on 110 degree days are expected. If comfort slips, have a technician check it.

What size heat pump do I need for a 1500 square foot house?

The heat pump size for a 1500 square foot house cannot be set by square footage alone. Capacity depends on insulation, ceiling height, window area and direction, duct condition, and how much sun the house takes. A contractor should do a load calculation, often called a Manual J.

In the West Valley the cooling load usually drives the size, because summers are far harsher than winters. An oversized unit short cycles and does a poor job removing humidity, while an undersized one struggles in July. Ductwork also affects how much capacity actually reaches the rooms, so a chart is not enough.

How much does a heat pump cost?

The cost of a heat pump depends on the equipment and the work, so an honest number needs a visit. The main factors are the size and efficiency rating of the unit, whether it is single stage, two stage or variable speed, and whether the air handler, coil and thermostat are replaced too.

Ductwork condition, electrical upgrades, refrigerant line sets, permits, pad or roof work and the difficulty of access all change the price. Removing the old equipment properly is part of it too. Get a written quote that lists what is included and compare the equipment details.

What temperature does a heat pump stop working?

Modern heat pumps keep working at low temperatures, but their output and efficiency drop as it gets colder. The temperature where one stops supplying enough heat depends on the model and the house, which is why many systems add electric heat strips or a furnace as backup.

Cold climate models are built to keep going at lower temperatures than standard units. In the West Valley, winter lows rarely get low enough to stop a heat pump, so backup heat runs seldom. If your system seems to struggle in a cold snap, it may be the defrost cycle, low airflow or a fault rather than the weather.

When should you switch from a heat pump to emergency heat?

Switch from a heat pump to emergency heat only if the heat pump has stopped working or is clearly not heating, for example if the outdoor unit has failed or is locked in ice. Emergency heat uses electric strips or a backup furnace and is much more costly to operate.

Emergency heat runs the heat pump off. Do not leave it on because it feels warmer. It is not meant for ordinary cold weather, since the system uses auxiliary heat automatically when needed. If you have to use it, call a technician to find the cause. If you see sparks, smell burning or the outdoor unit makes loud noises, turn the system off.

How do I know if my heat pump has auxiliary heat?

You can tell your heat pump has auxiliary heat by looking at the thermostat and the air handler. A thermostat with settings labeled Aux or Emergency Heat, or one that shows an AUX or EM HEAT message, usually means the system has backup heat.

The indoor air handler may have electric heat strips behind a service panel, or the system may be paired with a gas furnace. The nameplate on the air handler often lists the heater kit size. A technician can confirm it in a few minutes. Auxiliary heat is not the same as emergency heat: auxiliary runs automatically when the heat pump needs help, while emergency is a manual setting.

How do I stop my heat pump from freezing up?

To stop a heat pump from freezing up, turn the system off, set the fan to On to melt the ice, and replace the filter. Common causes are a dirty filter, weak airflow, a blocked return, low refrigerant or a failing fan.

Some frost on the outdoor coil in cold, damp weather is normal, and the defrost cycle clears it. A heavy block of ice or frost on the indoor coil is a problem. Melting can take hours, and you should not chip at the ice. If it freezes again, call a technician, because low refrigerant means a leak that needs a repair, and adding refrigerant takes EPA certification.

How much does it cost to run a heat pump?

The cost to run a heat pump depends on your electric rate, the efficiency of the unit, the size of the home, the outdoor temperature and how you set the thermostat. It is usually cheaper to run for heating than electric resistance heat because it moves heat instead of making it.

In the West Valley, most of the running cost is summer cooling. Your utility's rate plan matters, since time-of-use plans charge more at certain hours. Keeping the filter clean, ducts sealed and the thermostat steady will help. A clean coil and correct refrigerant charge also keep the system efficient.

How do I tell if I have a heat pump or a conventional AC system?

You can tell a heat pump from a conventional AC by checking the outdoor unit's nameplate. A model label that mentions heat pump, or a spec sheet listing heating capacity, is a clear sign. A heat pump also usually has a reversing valve.

The unit may run in winter with the fan on and cool air rising, or with frost on the coil. Another clue is the thermostat: if it has an Auxiliary or Emergency Heat setting and there is no gas furnace in the home, you likely have a heat pump. A conventional AC usually pairs with a gas furnace, which provides the heat. A technician can tell you in a minute.

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