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Heat Pump Effectiveness in Cold Weather

The majority of heat pumps work best when the temperatures are above 40 F; as soon as it becomes colder, the CoP (Coefficient of Performance) of air-source heat pumps drops. Investing in cold climate heat pumps and geothermal heat pumps will help you keep the house warm, even when it’s 0 F outside.

Not that long ago heat pumps were considered to be ineffective during the winter season and it was vitally important to have a backup heating source. However, today, thanks to new technologies, heat pumps have become more winter-friendly. 

What system should you go for? Let’s find out.

How Does a Heat Pump Work When It’s Cold Outside?

Unlike furnaces, heat pumps do not create heat, they pull it out of the outside air and then transfer the heat inside your house.

But what will happen to a heat pump, if it gets freezing cold outside? There certainly isn’t enough heat in the winter air, or is there?

In a nutshell, your heat pump would be able to extract heat from the air, even when the temperatures drop to 25 F or below. 

However, the system would require more energy to keep your house nice and warm. This, in its turn, makes the unit less efficient.

The majority of the heat pumps work best when it’s above 40 F.

Fun fact: air at 0 F contains 85% of the thermal energy that 70-degree air has. 

Another important thing that you should bear in mind is that heat pumps can freeze up in winter. 

When this happens, the unit switches to the defrost mode. This means that for a certain period the heat pump will be operating in cooling mode as only in such a case it is able to send hot refrigerant to the outdoor unit to melt the ice on it.

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Heat Pump Effectiveness in Cold Weather

The great news is that newer heat pumps have an improved ability to withstand freezing temperatures.

In recent years, the technology of the air-source heat pumps has made a giant leap forward. The majority of the system’s components were improved.

So, today you’ll find an air-source heat pump with:

  • An improved coil design
  • A two-speed compressor design
  • An improved electric motor
  • Thermostatic expansion valves that provide more precise control over the refrigerant’s flow
  • Variable speed blowers that not only boost the unit’s efficiency but can also work effectively with clogged air filters and blocked ducts
  • Copper tubing with internal gloves that help increase surface area

It is incredibly important to invest in the right equipment for your climate zone at the outset.

Special cold-climate heat pumps can keep your house warm even when the outdoor temperature gets to -12 F. Ideally, new houses should also be outfitted with solar panels and a tight building envelope.

With that being said, outside temperatures certainly do affect the CoP (coefficient of performance) of the heat pump.

If a heat pump requires 1 watt to produce 4 watts of energy, the CoP of such a unit is 4. 

But these 3 extra watts come from either the ground or the air which means that the coefficient of performance of an air-source heat pump fluctuates and depends on the amount of heat that it was able to extract from the outside air.

The great news is that the CoP of a geothermal heat pump stays pretty much the same. 

Read: The Most Efficient Way To Use A Heat Pump

Should I Use Backup Heating?

If you don’t have a highly efficient heat pump that can withstand freezing temperatures just yet, it might be a smart decision to have a backup heating plan.

  • If your house has natural gas connections, then you can go for a gas furnace. They provide efficient and reliable heating even on the coldest evenings.Such a ‘dual-fuel system’ takes advantage of the strengths of both electricity and propane.Tip: replacing an ordinary furnace with a dual-fuel system might qualify you for a rebate from your Cooperative.
  • You can also choose to install heat strips within the HVAC system (inside the air handler). They aren’t extremely efficient, but will certainly keep you warm.The system can turn on the heat strips in defrost mode when the heat pump switches to cooling mode to melt the outside ice.In such a case, the heat strips help balance out the temperature, so you might not even notice that your heat pump is in cooling mode.

Hint: use your backup heating only once the temperatures drop below 25 F. Otherwise, you are going to drastically increase your heating costs. 

Read: What Is The Difference Between A Heat Pump And A Furnace?

What Is AUX Heat?

Aux or auxiliary heat is referred to your heat pump’s backup heat source (a furnace, a heat strip, and so on). 

There are heat pumps that don’t have AUX at all, while others are installed with this optional add-on.

Hint: professionals can configure your system to switch to backup heating automatically as soon as the outside temperatures drop to the chosen setting. It will make the unit switch back to the heat pump as soon as there is such an opportunity.

Even though AUX heat is a normal part of your heating system, it can make your energy bills skyrocket. If you don’t want to spend a small fortune, then you should try to minimize the usage of auxiliary heat.

What can cause your AUX heat to come on?

  1. In a lot of cases, a change in the thermostat settings that are greater than 5 F can trigger the auxiliary heat. Try to change the temperature slowly and a few degrees at a time, if there is such a need.
  2. A sudden drop in the outside air temperature can also make your system turn to AUX heat.
  3. Finally, you might simply forget to close the door or the windows, for example. This will cause a temperature drop that is over 5 F and, you guessed it, the auxiliary heat will be triggered. 

Best Cold Weather Heat Pump

Geothermal heat pumps are amongst the most effective and environmentally friendly ways to keep your house warm.

The system consists of an underground loop of pipes and a heat-conducting fluid. The pipes, in their turn, are connected to the house’s ductwork system.

While the fluid is circulating in the underground loop, it collects heat from the ground. And this is the biggest advantage of a geothermal heat pump.

The temperatures above the ground tend to fluctuate a lot. However, the temperature about 10 feet below ground is pretty constant and stays at around 55 F.

In a nutshell, geothermal heat pumps always have enough heat to absorb and their CoP doesn’t change throughout the year.

Read: What Is The Most Efficient Heating And Cooling System

What Is a Cold Climate Heat Pump?

Cold climate heat pumps or CCHPs have been tested in Canadian winters for over a decade already.

These heat pumps are able to achieve high levels of efficiency even during the cold season thanks to an inverter compressor design.

At temperatures above 47 F, CCHPs operate with an efficiency close to 400%. When the temperatures drop to zero, the heat pump will still have an efficiency of around 200%.

That means that for every unit of energy consumed, a cold climate heat pump is going to deliver 2-4 units of heating energy (even on an extremely chilly morning).

Here are a few things that distinguish a cold climate heat pump from an ordinary air-source heat pump:

  • CCHPs have a higher HSPF (Heating Season Performance Factor). Ducted systems have an HSPF of 9 or higher and ductless mini-split systems – 10 or higher.
  • Each heat pump has a variable-capacity compressor.
  • The units are installed with a crossover set point of around 0 F (to ensure heating season operation). 

At the moment, it will cost you up to $7.000 or more to install a cold climate heat pump. However, you will be able to save, on average, 30-50% on your monthly energy bill, if you decide to go for such a heating and cooling system.

Tip: you might get a rebate on a CCHP that is worth up to $400.

People who live in a small house or in a home with an open floor plan will benefit from the biggest savings.

Before installing a cold climate heat pump (or any heating system), you have to make sure that your house is well-insulated and that the ductwork is not leaky (if you have one). 

These factors will drastically lower the efficiency of any heating system, so get your place ‘heat pump ready’ beforehand.

Read: What Size Heat Pump Do I Need?