Aeroseal vs Traditional Duct Sealing: Why Heat Pumps Expose Bad Ductwork Fast

Summary: Heat pumps run longer and deliver lower-temperature air than furnaces, so duct leaks show up immediately as cold rooms, drafts, and higher electric use. Traditional sealing works when ducts are accessible. Aeroseal seals hidden leaks from the inside and often delivers bigger comfort gains for whole-home heat pump systems.

You can get away with bad ductwork when you have a furnace. You absolutely cannot when you install a heat pump.

That’s one of the biggest surprises Massachusetts homeowners run into after upgrading. The heat pump is quiet. Efficient. Technically working perfectly.

And yet…one bedroom is cold. The hallway feels drafty. The system runs longer than expected.

Here’s the uncomfortable truth: heat pumps don’t create duct problems. They expose them.

Let’s break down why, and whether Aeroseal or traditional duct sealing makes more sense in your home.

Why Heat Pumps Reveal Duct Problems So Quickly

A traditional gas furnace blasts hot air at 120–140°F.

A modern cold-climate heat pump typically delivers air around 90–105°F.

That lower supply temperature is not a flaw. It’s how heat pumps achieve high efficiency. They move heat instead of creating it through combustion.

But here’s the catch:

If your duct system is leaking 20–30 percent of the air into your attic, basement, or wall cavities, a furnace can sometimes overpower that loss. A heat pump cannot.

Because it operates with lower air temperature and longer run times, every bit of duct leakage shows up immediately as rooms that never quite get comfortable, higher electric usage than expected, imbalanced airflow, and longer system cycles.

I’ve been doing this work in Massachusetts for two decades, and I can tell you: in homes built between the 1960s and 1990s, we routinely measure duct leakage between 20 and 40 percent before any sealing is done.

That’s a huge problem once you electrify.

What Is Traditional Duct Sealing?

Traditional duct sealing means physically accessing duct joints and sealing them using mastic sealant, foil HVAC tape, and mechanical fasteners.

It works best when your ductwork is exposed in a basement, you have access to the trunk line, and the system is relatively simple.

The pros:

Lower upfront cost. Straightforward process. Very effective for accessible ducts.

The limitations:

You cannot reach ducts buried in ceilings or walls. It’s labor-intensive. And you may still miss internal leakage at connections you simply can’t get to.

For unfinished basements in towns like Framingham, Natick, or Marlborough, traditional sealing often gets you 70–80 percent improvement at a reasonable price.

But what about ducts you cannot see?

What Is Aeroseal?

Aeroseal is a patented duct sealing technology that seals ducts from the inside.

Instead of manually sealing joints, the system pressurizes your duct system, injects a fog of polymer particles, targets leaks from the inside, and seals gaps up to 5/8 inch.

The process is computer-monitored and produces a before-and-after leakage report. In many homes, we see reductions from 25–35 percent leakage down to 3–5 percent.

That is a massive difference for a heat pump system.

Why Heat Pumps Make Aeroseal More Valuable

Heat pumps rely on balanced airflow, proper static pressure, and consistent return air pathways.

When ducts leak, conditioned air escapes, attic or basement air gets pulled into the system, and rooms at the end of long runs underperform.

Because heat pumps run longer cycles at lower temperatures, even small leaks compound over time.

Here’s how I explain it to homeowners: If you’re investing $20,000 to $40,000 in a whole-home heat pump system through programs like Mass Save, it makes very little sense to leave a 30 percent hole in your delivery system.

It’s like buying a new car and driving with one tire half inflated.

When Traditional Sealing Is Enough

Traditional sealing may be sufficient if your ducts are fully accessible, leakage is moderate, you’re not converting to full electrification, or budget is tight.

For partial heat pump systems or hybrid setups, this can be a smart middle-ground solution. Especially in older Colonials where trunk lines are exposed in the basement and we can get to most of the connections.

I’ve done plenty of traditional duct sealing jobs that made a real difference. It’s not that the method doesn’t work. It’s that it has limits.

When Aeroseal Is the Smarter Investment

Aeroseal tends to make sense when you’re installing a whole-home heat pump, ductwork runs through finished ceilings, you have comfort imbalance issues, you want documented performance verification, or you’re planning to stay in the home long-term.

In electrification projects across Newton, Needham, and Wellesley, Aeroseal frequently becomes the difference between a “good” system and a “why didn’t we do this sooner” system.

The data backs this up. We’ve seen homes go from barely functional duct systems to tight, efficient distribution networks in a single day.

The Hidden Cost of Ignoring Duct Leakage

Bad ducts do more than waste energy.

They can pull insulation fibers and dust into airflow, create negative pressure in parts of the house, increase humidity issues, and stress blower motors.

And once you switch from fossil fuels to electricity, every inefficiency shows up directly in your electric bill.

Heat pumps are incredibly efficient machines. But they require an equally efficient delivery system.

What We Actually See in the Field

Here’s what duct leakage typically looks like in Massachusetts homes:

Pre-1970 homes: 25–40% leakage 1970–2000 homes: 20–35% leakage Post-2000 homes: 10–20% leakage

Target after sealing: Under 10%, ideally under 5% for high-performance heat pump systems

Those numbers aren’t theoretical. They’re what we measure with actual diagnostic equipment before and after we seal ductwork.

The Bottom Line: Fix the Highway Before Upgrading the Engine

Your ductwork is the highway. Your heat pump is the engine.

If the highway has potholes, detours, and holes in the pavement, even the best engine cannot perform well.

Traditional duct sealing works. Aeroseal works better when access is limited or performance matters most.

The real mistake? Installing a high-efficiency heat pump without evaluating the duct system feeding it.

I’ve seen too many homeowners spend big money on a beautiful new heat pump system, only to be disappointed by uneven temperatures and higher-than-expected electric bills. Not because the heat pump wasn’t doing its job, but because 30 percent of the conditioned air was leaking into spaces that didn’t need it.

In Massachusetts, heat pumps don’t create duct problems. They just refuse to hide them.

If you’re considering a heat pump upgrade, or you’ve already installed one and aren’t getting the comfort you expected, it’s worth having your ductwork evaluated. Because no matter how good the equipment is, it can only work as well as the system delivering the air.

Want to know if your ducts are the problem?

If your heat pump is running but comfort still feels off, a duct leakage evaluation can tell us what’s happening fast. Call Endless Energy at 508-299-5561 or self- schedule an appointment through goendlessenergy.com. We’ll help you get the comfort you expected, and the “Endless Solutions” to match.

Aeorseal vs. Traditional Duct Sealing FAQs

Do heat pumps work poorly with leaky ducts?

Yes. Heat pumps are more sensitive to duct leakage than furnaces because they deliver lower-temperature air and run longer cycles. When ducts leak 20–30 percent of conditioned air, rooms feel uneven, drafts increase, and run times get longer.

Unlike furnaces that blast very hot air, heat pumps rely on steady airflow and balanced pressure. If air escapes into an attic or basement, performance drops quickly.

The equipment may be fine. The delivery system may not be.

What is Aeroseal and how is it different from traditional duct sealing?

Aeroseal seals duct leaks from the inside, while traditional duct sealing uses mastic or foil tape on accessible joints. Aeroseal can reach hidden leaks inside walls and ceilings that manual sealing cannot access.

Traditional sealing works well when ductwork is exposed in a basement.

Aeroseal works best when ducts are buried behind finished surfaces or when documented leakage reduction is important.

When is traditional duct sealing enough?

Traditional duct sealing is usually enough when ductwork is fully accessible and most joints can be physically reached and sealed.

It makes sense when:

• Ducts are exposed in an unfinished basement

• Leakage levels are moderate

• You are not doing full electrification

• Budget is limited

If we can reach nearly all connections, traditional sealing can deliver strong improvements.

How much duct leakage is common in Massachusetts homes?

In many Massachusetts homes built between the 1960s and 1990s, duct leakage commonly ranges from 20 to 40 percent before sealing. Even newer homes often measure 10 to 20 percent leakage.

For high-performance heat pump systems, the goal after sealing is:

• Under 10 percent leakage

• Ideally under 5 percent

Those numbers come from field testing with diagnostic equipment.

Should I seal ducts before installing a whole-home heat pump?

In most cases, yes. Sealing ductwork before installing a whole-home heat pump helps ensure balanced airflow, proper static pressure, and consistent comfort.

Installing high-efficiency equipment without addressing duct leakage can lead to uneven rooms and higher electric usage.

At minimum, ductwork should be evaluated before electrification.

Can Aeroseal fix rooms that never get comfortable?

Often, yes. If air is leaking before it reaches distant rooms, sealing those leaks can improve airflow and temperature balance.

Aeroseal does not fix improper system sizing, but it frequently corrects comfort issues caused by hidden duct leakage.

We often see noticeable balance improvements immediately after sealing.

Does duct sealing improve indoor air quality?

Duct sealing can improve indoor air quality by reducing the amount of dusty attic or basement air pulled into the system through leaks.

While it is not a complete air quality solution, sealing ductwork reduces unwanted infiltration and supports cleaner system operation.

Proper filtration and maintenance remain important.

How do I know if my ductwork is leaking?

Signs of duct leakage include uneven room temperatures, drafts near registers, long system run times, noisy airflow, and higher-than-expected electric bills after installing a heat pump.

The only reliable way to confirm leakage is through a diagnostic duct leakage test that measures how much air is escaping.

If comfort is inconsistent after a heat pump install, duct evaluation should be one of the first checks.