Do you need great insulation for a heat pump?

Skeptics claim that a heat pump—a super-efficient, all-electric heating and cooling system—can’t work if your home doesn't already have top-quality insulation. And some heat pump incentive programs only give out the biggest rebates to homes with decent insulation and air sealing.

Technically, you don’t need insulation to use a heat pump. As long as you properly install a big-enough system that suits your local climate, it’ll keep up with your thermostat—even in very cold parts of the world.

That said, a super-sized heat pump isn’t always the smartest way to spend your money, and your home might not feel as comfortable as it could—especially in parts of the US with harsh winters or summers. This is all true for any kind of HVAC system, but it matters a little more with heat pumps.

You can almost always find something to improve about your home’s insulation and air sealing—also called weatherization, the shell, or the envelope.

At a certain point, though, extra insulation stops being cost effective. Further down the line, extra improvements won't make the house more comfortable, either.

It helps to start by pinning down what exactly you're hoping for out of a heat pump and any related upgrades.

• Are you mostly trying to save money?

• Trying to make your home more comfortable?

• Trying to minimize your total energy use and environmental impact?

From there, you'll have a better idea about where to draw the line on the budget and scope of any insulation upgrade.

It's wise to get an energy audit

An energy audit is the simplest, most productive way to figure out if and how you ought to upgrade your insulation. High-quality audits performed by energy raters or home performance professionals usually cost a few hundred dollars after incentives. It should include a blower-door test, a report with an energy score, and suggested next steps. (Free energy audits often do not include many of those elements.)

What if the energy auditor finds that your home is pretty tight and doesn’t have any low-hanging fruit for you to fix? It’s still money well spent, because an HVAC contractor can use some of the auditor’s measurements to choose the best possible heat pump for your home.

Other clues you might need insulation

Are there any rules of thumb that your home’s shell might be OK as is? The home performance and energy efficiency pros we talked to were hesitant to offer any. “There are way, way too many exceptions,” said Jeremy Begley, partner and co-founder at building performance firm HVAC Design Partners and the HVAC 2 Home Performance training academy.

That said, there are a few clues that your house could probably use some tightening up:

• If your house is already uncomfortable, a heat pump won’t make it better. If your home feels drafty, and can’t hold steady temperatures for long whenever the HVAC system cycles off, it’s usually a sign you should weatherize your house. It’s true that heat pumps can make your home more comfortable than traditional HVAC in some important ways, but this is not one of them. 

• The age of the home isn’t a reliable sign of efficiency, but might give you some idea. Energy codes first took shape in the 1970s following an oil crisis, so homes built or rehabbed since then are more likely to have decent insulation than older, un-renovated homes. That said, building codes are developed and enforced locally, and air sealing was an afterthought pretty much everywhere until the 2010s according to Begley. So a newer building is no guarantee of comfort and efficiency. 

• Get familiar with how decent insulation should look around your house: We cover some of the basics below. Check the attic, check the crawlspace or basement, even try to check the ductwork. 

• Insulation matters more in harsher climates. If you live on the west coast where it’s temperate and dry, insulation is less important because your HVAC system doesn’t work as hard. In parts of the US where it’s very cold or very humid for long stretches of the year, it really pays to have a well-weatherized home.

Once you understand the scope of what improvements you could make, it’s a matter of what your original goals were.

Strictly focused on the economics? Pick the insulation projects with the shortest payback periods. More on that next.

Willing to pay more for comfort? Go in on the upgrades that cost more but keep you feeling cozier in your home. More on that further below.

Better weatherization should help you spend less on a heat pump and less on energy, and might help you avoid expensive upgrades to your ductwork and electrical panel.

But how fast (if ever) will you recoup your insulation investment? Based on what we’ve learned from expert sources and studies, it really depends.

• Pretty-good insulation can cost anywhere from $1,000 to $15,000.

• That insulation could save you anywhere from $2,000 to $35,000. That's through the cost of the heat pump equipment, other infrastructure upgrades, and energy bills over 10 years.

Easy payback: In a leaky, poorly insulated home, the money you spend on weatherization should come back to you quickly, especially if you live somewhere with harsh weather. Even small improvements can make a huge difference here.

“Air sealing and insulation is cheap compared to heat pumps, particularly if you have to tip over to using two heat pumps,” says Edward Louie, a Building Energy Efficiency Research Engineer at the Department of Energy’s Pacific Northwest National Laboratory. 

Slower payback: On the other hand, homes that are already pretty tight and well-insulated might never earn back the upfront costs of extra weatherization. The first few inches of insulation do the bulk of the work, for example, so it might not be cost-effective to max out the R-value in your attic.

Case study: Bungalow near Boston

I’ll use my house as an example. It’s a bungalow outside of Boston built in 1920, with about 2,200 sq ft of living space including a finished basement and attic. 

As insulation and air sealing have been upgraded over time, the heating and cooling loads have changed massively compared to the original condition. I used CoolCalc to get these numbers, then ran them by Begley, the home performance pro, who said “they seem reasonable.” (More on loads and heat pump sizing here.)

The first update (made before we moved into the house) was a slapdash job without much attention to detail. According to the modeling software, it still cut the heating load by about 40 percent.

The second update still wasn’t perfect by the modern standards of building science and home performance. It was cheap, however, thanks to a local incentive program. Software says that it reduced our heating load by another 30%, and the real-world gas bills say that we used about 25% less energy on heating. It also brought us under the crucial 5-ton threshold, which saves a ton of money on install costs.

If we were to weatherize up to the best-case scenario for a building like ours (short of a gut rehab), we’d save a little more across the board. It would likely trim our heating and cooling bills by at least another 10%, and could cut the cost of a heat pump installation by about $1,000. It also means that a properly sized heat pump should fit existing ductwork—no major renovations needed, no comfort compromises necessary.

An energy auditor / home performance pro can help with your cost-benefit analysis, but here’s what we’ve learned about pricing.

Insulation costs

Assuming you’re planning to hire a pro, the cost of common-sense insulation is likely between $1,000 and $15,000. 

Generous incentive programs like Mass Save can keep the out-of-pocket costs toward the lower end of the scale (though most parts of the country don't have a program like that).

The Department of Energy’s most recent study, from 2015, found that the typical cost was about $6,800 per home before incentives, though today’s costs are likely higher than that due to inflation. Brett Little, the Education Manager at the GreenHome Institute told EnergySage that as of a few years ago it was more like $8,000 to $10,000 per home, and now it could be closer to $15,000, maybe even $20,000.

Equipment costs

A leakier house needs a bigger heat pump. Every extra ton of heating capacity can cost an additional $500 to $1,500 or more just on the cost of equipment. Here are some examples, for two of the most popular heat pumps on the EnergySage Marketplace:

Mitsubishi H2i Hyper-Heat M Series, Ducted Heat Pump

Source: GotDuctless.com, January 2024

Bosch IDS 2.0 BOVA18, Ducted Heat Pump

Source: BudgetHeating.com, January 2024

Barely-insulated houses in cold climates often need 6 tons of heating capacity or more. The biggest single residential heat pump is 5 tons, so a drafty house might actually need two heat pumps. This drives the cost of installation way, way up, as shown in the real-world data from the EnergySage Marketplace.

Median heat pump installation cost, ducted and ductless

Source: EnergySage Marketplace, 2023

So it really pays to try to get that heating load down, and the first few steps toward better insulation make the biggest difference.

*Why do 5-ton systems cost less on average than 4-ton systems? I wish we knew.

Energy costs

Leakier homes also spend more on energy. So when you tighten up the shell, you’ll start racking up long term savings on your utility bills.

EnergyStar estimates that homes without common-sense, cost-effective weatherization will pay about 15% more for energy every year.

In the real world, it'll vary by climate and how leaky the house was in the first place. We crunched the numbers from a DOE database, and the differences can be much more dramatic than that: Tightening up an inefficient home so that it’s just average should cut energy use by 65 percent.

(The energy savings when you jump from average to very efficient are even more dramatic, though it looks like most of the super-efficient dwellings are in large, multi-unit buildings, with lots of shared walls.)

Ductwork costs

Heat pumps need bigger ducts than traditional heaters—at least if they’re to work efficiently, quietly, and without over-stressing their fans. “You cannot install a heat pump and have it blow through a straw,” Louie says. The problems with old, skinny ducts are most pronounced on the coldest days of the year, when the heat pump has to really crank. 

It’s hard to overcome a huge mismatch between the old ducts and a new heat pump. In borderline cases, though, you might be able to weatherize your way out of a duct reno. Ductwork that’s sized for central AC, for example, stands a better chance of working well with a new heat pump if you can get your home’s heating load down a bit.

What could you save? A duct renovation typically costs between $1,000 to $5,000, according to Begley.

Electrical costs

Reducing your loads could also help you avoid an electrical panel upgrade. It’s possible to fit a heat pump onto 100 amps of service, even alongside all kinds of other electric appliances. There’s no guarantee that this will work, though, especially for a larger-than-average all-electric home in a cold climate.

Solar costs

Finally, reducing your heating loads could also help you install a smaller, less-expensive rooftop solar panel system, if that’s something you’re interested in getting at some point. HVAC uses more energy than any other system in a typical home—which means you’ll need a lot of solar panels to offset its energy use. We estimate that it’ll take between 9 and 13 panels to power a typical whole-house heat pump, though the true count can be much, much higher. Each panel costs about $1,200 installed on average, so each panel you don't need to install ends up saving big money.

Even if you don’t earn back your investment, better insulation, air sealing, and ductwork can make your home much, much more comfortable—and that’s priceless.

High-performance heat pumps can keep your home cozier than traditional HVAC in some profound ways. Your home’s air temperature and humidity should stay almost perfectly steady. It’s a big change from the ups and downs you get throughout the day with a typical furnace or central AC.

But heat pumps (and most HVAC in general) can’t really fix two other important factors in human thermal comfort: Cold walls and cold air leaks—or in the summer, a hot roof and humidity leaking inside. 

Cold walls: The biting chill that comes from sitting near a cold wall can actually be measured: The mean radiant temperature. The greater the temperature difference between your body and a cold surface nearby, the more our nerve endings feel the heat being sucked away. Insulation is the most foolproof and energy-efficient way to keep the walls warm, so the heat transfer from your body is slower and not as noticeable. (During the summer, it’s the same phenomenon in reverse.)

Cold air leaks: Our skin also picks up on very subtle air movements, measurable as relative air velocity. It doesn’t need to be a big gust—even a consistent trickle can feel raw. Air sealing is an easy, inexpensive, reliable way to eliminate the big drafts.

Heat pumps are uniquely sensitive to bad insulation

Any kind of forced-air HVAC system will struggle with cold walls and air drafts. Heat pumps might have an even harder time overcoming those challenges, because they don’t run as hot.

The highest temperatures you’ll measure coming out of a cold-climate heat pump are about 120 F, but it can be as low as 90 F. A furnace blows air at about 140 F, and that higher temperature helps cover up some of the challenges of heating a drafty home. Cold air that leaks into the home can create “convection loops and hot and cold spots,” Begley says. “That’s not going to be overcome by the heat pump. It’s actually going to be exacerbated by it, because it’s a little bit lower temperature, and it takes longer to heat the air.”

Several experts also stressed that high-performance inverter heat pumps are sensitive to leaky ductwork in ways that traditional HVAC is not. The lower air temp has something to do with it, but it’s also because they run at low speeds. Slow air movement in a leaky duct means very little heating or cooling actually makes it all the way to the vent. Modern heat pumps are generally smart enough to adjust for this by blowing more air—though it also means they’ll use extra energy.

There are a few schools of thought about the best ways to get the biggest bang for your buck when you’re weatherizing your house. But a few common themes emerge.

• Check the attic first. “Every weatherization assistance program does attic air sealing and insulation first,” says Louie, the DOE researcher. It’s almost always responsible for an outsized amount of air leaks and heat loss in the house, especially if some of your ductwork runs through the attic. Even if your attic has existing insulation, look for signs of moisture or rodents—you’ll want to replace any old, dirty material, and take some steps to prevent it from happening again. Energy Star has some guidance on attic air sealing and insulation, and YouTube is rich with how-to videos from respected pros. You can DIY a lot of attic-efficiency upgrades, but it’s tough work.

• Make sure the ducts are in good shape. “If you’re going to have a heat pump installed into ductwork, that ductwork cannot suck,” Louie says. This step isn’t always included in advice about weatherization, but it’s really, really important for cold-climate heat pumps. Duct sizing is one part of this, as we’ve covered. But you should also aim to minimize air leaks and air resistance. This part is tough to do yourself, and is probably best left to a pro. 

• Close other obvious air leaks. Gaps around door frames, window frames, outlets, recessed lights, outdoor spigots, dryer vents—these can all add up to significant leaks. Begley, the home performance pro, shared a case study a case study on the dramatic effects that air leaks can have on heating, cooling, and dehumidification loads. “Air sealing can have just as much (if not more) impact as insulation alone,” he wrote. EnergyStar has some tips on how to start air sealing some common problem areas, if you want to make improvements on your own. 

• Tighten up the space under your home. Crawlspaces and basements need slightly different approaches, but they both involve some modest insulation and air sealing to keep the heat in and the moisture out. EnergyStar once again offers some guidance. Homeowners can handle some but not all of these jobs.

• Fill the walls where you can. Dense-pack blown-in cellulose insulation, aka drill and fill, is usually the most practical way to insulate and air-seal empty cavity walls whenever a gut-rehab isn’t in the cards. It’s a big job for a professional crew, but the costs are reasonable for how big of an improvement it makes to your home’s comfort and efficiency.

Not every step will be practical in every home, but each upgrade you can do will make your home more comfortable, and help you save money on HVAC.

A comfortable, efficient heat pump system starts with the installation. The EnergySage Marketplace makes it easy to get quotes from experienced, vetted heat pump contractors (in select areas).

Have more questions about heat pumps? When you sign-up (free of charge!) for the marketplace, we'll connect you with an EnergySage Energy Advisor—one of our in-house heat pump experts who can help guide you through the installation process.

And don't forget: When heat pumps run off of renewable, zero-emissions electricity from solar panels, they're even better for the environment and can even eliminate your heating and cooling bills entirely. The EnergySage Marketplace can help you find a top-quality solar installer in your area, too.

Photo credits: iStock