Here in Atlanta, our winters are relatively short and mild compared to other parts of the country. By late March, we’re often experiencing full-blown springtime weather!

But that doesn’t mean it never gets cold here. In fact, we rarely escape a winter without experiencing at least a few days of sub-20 degree temperatures. Occasionally, nighttime temperatures dip into the single digits. That’s cold!

So, what happens if you have a heat pump when these big cold snaps hit? Does the system struggle to heat your home?

If your heat pump struggled this past winter, you might be wondering whether you should do something about it. You might be contemplating a new system – a furnace, perhaps? – or maybe you’re wondering if you can make some adjustments to the existing system in an effort to keep your house warmer.

Let’s take a closer look at why heat pumps sometimes struggle in extreme cold and what you can do about it.

1. Older heat pump systems were designed for minimum outdoor temperatures of 24 degrees

It’s really that simple.

If you’ve got an older heat pump system and there were a few nights where it didn’t keep your home toasty, it’s not necessarily the heat pump’s fault. In many homes, the “classic” heat pumps installed in our climate zone weren’t designed to perform in sub 20-degree outdoor temperatures.

The heat pump is working the way it’s supposed to. It’s just going to struggle during those rare instances of extreme cold.

Example: Last winter, it got down to 5 degrees one night. We got calls from people whose systems weren’t heating their homes to more than 60 degrees. To be clear, the heat pump was heating properly – a home that’s 55 degrees is a lot warmer than the 5 degrees outdoors – it just wasn’t meeting the homeowner’s expectations for comfort.

If this sounds like you, you’ve got a couple of options (aside from using space heaters to power through the cold snap):

  1. Air seal your home and beef up the insulation:We’ll cover this in greater depth below, but air sealing can be a super impactful home performance upgrade! Ditto for insulation improvements. Homes with older heat pumps tend to be older homes. Most of the time, these homes have lots of air leakage and less-than-perfect insulation (it might be old, damaged, or poorly installed). Improving the home can make it easier for the system to heat your home in winter.
  2. Upgrade your heating system: Whether you get another heat pump, a gas furnace, or a dual fuel system, you’ve got options! Many new heat pumps do a much better job heating during freezing temperatures than the old ones. This person heats his Minnesota home with a heat pump and keeps plenty toasty.

If you already have a heat pump and don’t have existing gas lines running to your home, rest assured that new heat pumps are much more capable of heating your home during the extreme cold. We can help you select a size and type that will keep you warm even when temperatures dip into the teens and single digits.

Keep in mind that if you install, say, a 15 SEER2 standard heat pump, it will be more efficient than your old system but you will likely have the same problems during extreme cold. New variable speed heat pumps will provide additional heating capacity at lower temperatures compared to standard units.

If you do have gas lines running to your home, consider a dual fuel system. Heat pumps are most efficient during those “cool-but-not-super-cold” days when it’s in the high 30s to the low 50s. After outdoor temperatures enter into freezing territory, heat pumps often rely on auxiliary heat strips for heating – these are a type of electric resistance heat that’s really costly.

With a dual fuel system, a gas furnace turns on instead of the heat strips. So when it’s really cold outside, you get the benefit of a more efficient gas furnace. When it’s cold but not super cold, you use the heat pump – a best of both worlds arrangement!

2. Your home is inadequately insulated and/or air sealed

We mentioned this above, but let’s go over it in a little more depth.

In addition to obvious physical barriers from the outside world (walls, roofs, etc.), your home has a few less-obvious barriers. Two of those are its air barrier and thermal barrier.

The air barrier partially consists of walls, windows, and roofs, but it also includes materials installed in gaps and cracks to prevent the flow of air into and out of the structure. When there’s a lot of air flowing into and out of these gaps and cracks, we call it air leakage.

The more air leakage you have, the more difficult it is for your heating system to heat your home. A lot of the hot air it produces escapes very quickly through the unsealed gaps and cracks!

As a result, your home feels colder, less comfortable,and more drafty than it should.

A lack of effective insulating material poses a similar problem. Also the word “effective” is key here. A lot of homes with insulation aren’t benefiting much from the insulation they’ve got because it wasn’t installed properly. Insulation forms your home’s thermal barrier, which means it blocks the passage of heat in either direction.

In winter it blocks heat from leaving your home. In summer, it blocks heat from entering your home.

To be effective, insulation must be carefully installed in the right places. Great care must be taken to ensure the insulation is properly sized, cut, and placed into attics, walls, and crawlspaces. In addition, it needs to be regularly inspected for damage, movement, or other changes that would compromise its performance.

Given the above, it’s not hard to see how homes with poor insulation, zero air sealing, and older heat pumps that struggle in sub-20s temperatures might feel pretty cold when it’s 12 degrees outside!

Air sealing the largest gaps and cracks in your home’s building envelope and re-insulating areas that lack adequate insulating material can go a long way toward improving comfort in winter. That’s true whether you have an old heat pump, a new one, a gas furnace, or the world’s tiniest space heater.

3. You lose a lot of heat through leaky ducts

Let’s say you don’t even have an old heat pump anymore. You replaced it with a new one. You also air sealed all of your home’s largest air leakage spots and reinsulated in your attic and crawlspace. Have you ensured that you’re good to go for next winter?

Almost! But there’s one more potential source of heat loss we haven’t covered: leaky ducts.

In truth, an HVAC system will only perform as well as the ducts it’s connected to. A properly designed and installed duct system is absolutely essential for effective heating and cooling performance. Unfortunately, many installers neglect ductwork design during home construction and even during HVAC system replacement. The result is a furnace, heat pump, or AC that doesn’t keep people comfortable. The home’s occupant’s blame the equipment; often, the problem is the ductwork.

One common problem with ducts is that they’re just… wrong.

Wrong size. Wrong installation. Wrong run lengths. Wrong number of angles. We’ve seen it all.

When the people installing ducts don’t perform the necessary calculations to determine what size ducts and how much of them you need, it’s really hard for your HVAC system to move air properly.

Another problem is leakage, and that’s what we’re going to focus on here.

Leaky ducts can compromise even the best designed duct system! Leaks occur when sections of duct:

  • Aren’t properly connected
  • Aren’t properly sealed with tape or mastic
  • Were sealed with tape that lost its adhesive properties and fell off
  • Don’t connect properly to the unit at the plenum
  • Get damaged by pests, contractors, or environmental conditions in the attic or crawlspace

The solution is to seal them! And replace any sections of duct that can’t be sealed.

You can eyeball your ducts and seal them with mastic tape or actual mastic paste. A better solution is to have a contractor perform a smoke test to identify all the leaky areas and seal them. That’s how we approach duct sealing at PV. With this “test and seal” process, we get duct leakage down to 4% in virtually every home – that’s really really low duct leakage!

Sealing up your leaky ducts helps ensure that the heat your heat pump produces actually makes it into your home. When the ducts leak, a lot of that air is lost to your crawlspace or attic.

4. Other possibilities

While the above problems are the most likely reasons your heat pump struggled this past winter, there are a few other possibilities to consider:

  • The refrigerant charge is off. When this happens, you might see a layer of ice form on the system’s outdoor unit – not a thin layer of frost (that’s normal), but a thick layer of ice. Needless to say, the heat pump can’t bring in much heat from its environment when it’s covered in ice. It’s going to struggle big time and it might even break down.
  • There’s a problem with the defrost cycle. It’s normal for your heat pump to frost over a bit in winter. When it’s working properly, the defrost cycle will turn on and melt the ice from the outdoor coil. But if there’s an issue with the defrost cycle, the system might not melt the ice. You will end up in a similar situation to the refrigerant issue above.
  • The heat pump is undersized. This is less common (more often, heat pumps are oversized), but it’s still possible. An undersized heat pump will probably struggle to heat your home on the coldest days and nights, especially if you also have inadequate insulation, poor air sealing, and a lot of duct leakage.

You shouldn’t have to deal with a heat pump you can’t rely on

At PV, we help people across Metro Atlanta address comfort problems every single winter. The right solution for you depends on a variety of factors, including the type of heating system you have, the extent to which your home is air sealed or insulated, and the condition of your duct system.

In recommending a course of action, we consider all of these issues to help you get the best possible solution for your home and your long-term comfort.

Get in touch today to discuss your home comfort issues! We’ll make an appointment to visit your home, analyze your situation, and point you in the right direction.

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