How Do Heat Pumps Work In Winter (Maintain Effectiveness)

Did you know that your heat pump can still work in temperatures as low as 5℉? This is because they can still extract heat from the winter air even though it is much colder than the spring or summer.

Heat pumps work in winter by capturing the heat from the outside air. Even though the temperature may be colder, there is still heat, and the heat from the winter air is warmer than the refrigerant temperature inside the heat pump coils, so the system can still function.

To understand how this can be possible, we need to look at a few specific aspects of the heat pump :

  • How heat pumps work
  • What temperature range heat pumps can work in
  • When would heat pumps not work in winter
  • How energy efficient is a heat pump
  • Tips to keep your heat pump in top condition for winter

Let’s turn up the heat on this technology and see how they work in the cold winter environment.

Heat pump at the back of a house with snow in winter

How Does A Heat Pump Work?

Unlike other devices that use fuel to generate heat or cold, such as conventional HVAC or water boilers, the heat pump moves heat from one place to another. When heating, it pumps heat into the home, and when cooling, it pumps heat out of the home.

All this is achievable through the innovative technology and design of the heat pump, making them extremely efficient and increasingly popular with homeowners looking for ways to reduce their energy bills.

The heat pump has two sections, the outdoor and indoor parts. The outdoor segment is where the warmth in the air is absorbed, and the indoor segment is where the warmth is pumped into the home.

What Is The Role Of The Refrigerant In A Heat Pump?

The heat pump concept is quite simple to understand. The first thing to understand is the role of the refrigerant, and the newer R410a liquid is the more environmentally friendly one being used in air conditioning and heat pumps around the world.

In its natural state, the refrigerant is a gas, and it is much, much colder than the outside air, even in winter. So the mental picture you may have is that of warmer air, but the reality is, it’s the very cold refrigerant that is the key.

This is why, even with the cold winter air, the heat pump can still heat your home as it uses the relatively warmer air from the outside. The air is moved over the coils where the gas is, and by the 2nd law of thermodynamics, heat energy flows from hot to cold.

The gas absorbs as much heat as it can from the air, and then the compressor converts the gas into a very hot liquid – this happens due to the compression, and the same principle applies when you pump your bike tire.

As the pressure increases as you pump, you find the air hose and valve getting hot; this is due to the temperature of the air increasing under pressure.

How The Indoor Section Of the Pump Transmits Heat To Your Home

Once the warm gas is compressed and converted to a very hot liquid, it is moved through to the indoor coils, where the blower releases the heat into the space. As the liquid loses all that heat, it transforms back to a gas and is cycled back to the outdoor coils, where the process starts all over again.

The heat pump is essentially a refrigerator moving warm air into the space rather than cold air, but when the heat pump has to cool, it simply reverses the process with the cols absorbing warm air from inside and pumping cold air back into the home.

What Is A Heat Pump’s Operational Temperature Range?

Heat pumps can operate in a wide temperature range and only when the outside temperature gets low, as in below freezing in ℉, where it may start to use more energy to generate heat.

Heat pumps have an effective operating temperature of 15 °F -115 °F; this is why they are so popular across the USA and are especially effective in the central and southern regions. These are where the temperate climates are.

Heat pumps are ultimately more efficient in temperate climates as even in winter, there is plenty warm in the air for the heat pump to operate effectively.

This doesn’t mean that a heat pump won’t work for you if you live in areas like Minnesota or Illinois, but it may mean that you need a backup heating system for when the temperatures dip well below zero.

As you move further north and northeast, the winter temperatures would drop below that -10℉ range, and there, the heat pumps may struggle to deliver heat, and those homes would require a secondary or backup heat source for the mid-winter months.

At What Temperature Would Heat Pumps Not Work?

When the outdoor temperatures approach the 40°F mark, the heat pump’s efficiency decreases and uses more energy to warm the interior space. If the temperatures dip below freezing at 32°F, you may need to activate an auxiliary heating system.

Overworking your heat pump is not a good idea, and if you live in areas where temperatures can drop below freezing, you should consider having a backup heating solution.

However, remember that because the refrigerant is so much colder than the air temperature, it may still be able to absorb warmth from the outside air and still provide heat to your home.

Does The Heat Pump Have A Defrost Function?

Heat pumps have a defrost function, which will activate if the system senses that the outdoor coils have frozen over, and this will happen when the outdoor temperature drops to 32°F or lower.

The heat pump will automatically switch to cooling mode and pump hot gas back to the coil to melt the ice. When in the defrost cycle, you will feel cool air pumped into your home as the heating cycle is reversed.

During this cycle, the indoor unit will be running, but the outdoor fan will be off, which should not affect your home’s indoor temperature at all.

Where you find big chunks of ice or snow that have caused the heat pump coil to freeze, you can activate the electric heating or auxiliary heating system and get an HVAC technician to come and check the heat pump as the built-in defrost system may not be enough to meet the large volume of ice or snow.

How Energy Efficient Are Heat Pumps?

Because heat pumps don’t burn fuel to create heat or cold but pump it from one space to another, they are supremely energy-efficient, making them a logical choice to reduce energy costs.

A heat pump used to replace a boiler is about 70% more efficient, and stand-alone heat pumps for water heating can deliver enough hot water for a family of four for around $15 a month!

The heat pump can reduce energy costs in an average home by around 50%-60% annually when it comes to air-conditioning.

Also, the larger the home, the more energy, and money would be saved by installing a heat pump. Considering that an installed heat pump could cost about $10 000 but save between $1000 and $1500 or more per year, the payoff for the heat pump is about 8-10 years.

What Are Factors That Affect Heat Pump Efficiency?

Several factors would contribute to the energy efficiency of a heat pump in winter and generally and they are :

  • Insulation
  • Windows (not the computer kind)
  • Size of the home

How The Insulation Of The Home Affects Efficiency

The quality and level of insulation in the home will directly impact the energy usage of the heat pump. Uninsulated homes will lose a lot of heat through the roof and ceiling, and in winter, this effect is even more pronounced.

This means that the heat pump will use more energy in winter to maintain the required temperature. Still, if the home is properly insulated and meets the regional insulation standards, you could look at a smaller heat pump, which would cost less.

Not only that, but proper insulation will keep the indoor environment at a consistent comfort level, and you wouldn’t notice or feel a difference in winter, and your energy costs would be lower.

How The Quantity Of Windows Affects A Heat Pump’s Efficiency

Aside from the ceiling and roof, the next biggest heat loss in a home occurs through the windows.

According to the Department of Energy, depending on how many there are and where they are, you may need to consider upgrading them to double glaze or energy-efficient windows as these will reduce energy costs by 25%-30%.

How The Size Of The Home Affects Heats Energy Efficiency In Winter

Whether in summer or winter, the home’s size and the number of windows and insulation are the three biggest factors to consider when installing a heat pump and achieving efficient energy usage.

Without a heat pump, a large home using fuel oil or an electric heating system will use considerably more energy to keep the home warm than a heat pump will as the more cold air has to be removed and the more heat pumped in.

The larger the home, the more money and energy you would save by installing a heat pump, especially in winter. With more space to heat, you may need a larger heat pump to be effective, but this will be offset against the savings achieved.

How To Maintain Your Heat Pump

To keep your heat pump operating at optimum throughout the winter and summer, there are some maintenance tips you can implement to reduce service costs and keep the unit running properly.

  1. Replace your air filter every 30-60 days. If the air filter is clogged, it will cause the heat pump to use more energy to pump air, increasing energy costs.
  2. Before winter sets in, remove any vegetation or debris like leaves, twigs, and branches that may have gathered near or on the unit. This can adversely affect the unit’s efficiency and freeze on to it in winter.
  3. Schedule HVAC services twice a year, preferably in fall and spring when the temperatures are milder, and the load on the unit will be less.
  4. Never stack anything on top of the heat pump, as this will prevent normal operation in releasing heat back outside and causing the unit to overheat.
  5. Ensure the unit is level and preferrably on a concrete base with a minimum two foot clearance around the unit to allow maximum absorption and release.
  6. Having shade around the heat pump from trees or awnings will improve its efficiency in summer.
  7. If you have electrical outages in winter and your heat pump is interrupted by an outage, you need to wait around 6-8 hours before turning it back on. Use the backup heating system in the meantime.
  8. If the power to your heat pump has been out for longer than 30 minutes, you should switch your thermostat to emergency heat mode and keep it there for at least as long as the outage was before turning your heat pump back on.
  9. If you don’t know how long the outage was, keep your emergency heating for between 6 and 8 hours before restarting; this will protect the compressor from failing under extreme load.

If you find your heat pump is running all the time, there may be other issues affecting the operation, and some of those you can fix yourself as discussed above, and the others below would require an HVAC technician’s assistance.

Some of the more technical issues for this could be low refrigerant charge or refrigerant flow issues, undersized equipment (although the correct sizing should have been done before installation), the unit may need cleaning and servicing, bad or poor reversing or compressor valves, iced up the outdoor unit, or the auxiliary heating may not be working.

By keeping your heat pump well maintained and upgrading your home’s insulation in the ceiling and windows, your heat pump will be able to operate properly in winter without too much struggle and keep your home warm for many winters to come.


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