Air Sealing vs. Insulation: What’s Better For Efficiency?

An energy-efficient home is one in which air doesn’t leak. This reduces your reliance on your HVAC units. Replacing your windows, doors, and weatherstripping might not be enough to make your home greener, though. You could also need insulation or air sealing. When it comes to air sealing vs. insulation, which is the better choice for energy efficiency?

Between air sealing and insulation, the former is more important for energy efficiency. Air sealing repairs air leakage points and is usually done before insulation is installed. Both methods in tandem can make your home even greener.

You might have a passing knowledge of insulation, but do you know of all the types, including blanket batts? That’s one thing we’ll discuss ahead. We’ll also talk about air sealing and why it’s worth doing, so make sure you keep reading!

What Is Air Sealing?

Let’s start by discussing air sealing. This may sound like a service that’s only useful if your home is noticeably drafty, but even homes where you don’t feel air leaking can benefit.

A picture of a hand being placed up to an open air vent in a house with gaps between the drywall and the air vent, letting hot attic hot air leaking into the house.
Ductwork is just one of several areas that can contribute to air leakage in your home.

For example, let’s say your home was built between 1970 and 1989 and is a four-bedroom property with 1,700 square feet of space. Energy Star estimates that your system ducts leak at a rate of 23 percent, and the window-to-floor-area ratio leaks at a rate of 15 percent.

What do you do when your home feels cold even with the heat on? That’s right, you crank up the heat. It’s the same story in the summer, when the air conditioner is on but your home won’t cool down. You blast the AC until you feel cool and comfortable.

These habits jack up your monthly utility bills. Just when summer ends and you get to turn off the air conditioner, here comes the cold, requiring you to run your heater. It’s a never-ending cycle. And it costs you a lot of money.

Air sealing can seal up your home’s leaks, from the crawl space to the attic and every room and space between. According to Energy.gov, here are the rooms/areas of a home that often need air sealing the most:

  • Common walls from one attached dwelling unit to another
  • Doors
  • Windows
  • Floors, including cantilevered floors
  • Foundations, including sill plates and rim joints
  • Garages
  • Fireplace walls
  • Penetrations in the exterior wall
  • Whole-house fans
  • Ducts
  • Recessed lighting
  • Attics
  • Chimney or flue shafts
  • Porch roofs
  • Exterior wall staircase framing
  • Soffits and dropped ceilings
  • Duct or shaft piping

How Air Sealing Works

If you’re wondering which parts of your home to seal, the answer lies with a blower door test. We’ve written about blower door tests in the past, so we won’t go into too much detail here, just a basic recap.

When you get a blower door test done as part of an energy audit, a certified operator will visit your home and attach a fan around your home’s exterior door via a frame. The fan pulls the air from your home, depressurizing it. This can reveal cracks, leaks, and openings.

technician performing a blower door test to find air leaks
Here’s what a blower door test looks like in action. This was one of the first steps in our first net-zero home renovation.

Air sealing is the solution. You can do air sealing yourself or hire a professional to do it. Based on the results of your energy audit, you’d seal the rooms that are draftiest so they don’t leak anymore.

Foam spray sealant can take care of most attic gaps except for recessed lights and chimneys. You can also use foam spray in your crawl space and/or basement, specifically areas such as heater vents, dryer vents, HVAC lines, and hose bibs around the foundation or rim joists. If you run out of foam spray in the attic, use caulk for your basement or crawl space.

To seal interior walls, you’ll need foam gaskets positioned behind your light switches and outlets. Caulk can seal up gaps around the baseboards, doors, and windows if these haven’t been replaced in a while. 

What Is Insulation?

The most basic definition of insulation is a material that fills or blocks gaps and holes in a home. Insulation can have all sorts of purposes, including noise reduction, but most people install insulation primarily to control their home’s temperature.

photo of pink fiber insulation being installed between wall studs in a house
Insulation can be tucked into every nook and cranny to keep your home’s temperature stable. Photo by Erik Mclean on Unsplash

How? Heat moves, starting in a warmer zone and continuing to a cooler area. This means that in the winter when you run your heater, that heat will try to escape the house or at least move towards the cooler parts of your home. In the summertime, heat tries harder to come in since it gravitates towards cooler areas such as your air-conditioned house.

Insulation can prevent heat from moving as quickly, which has different benefits depending on the season. Throughout the summer, an insulated room maintains its cool temperature so you can use your air conditioner less. Then, in the winter, less heat will exit your home so it’s cozy and warm.

Types of Insulation

Not all insulation is the same. Here are the various types and what they’re intended for.

  • Radiant or Reflective Barrier Insulation

Radiant or reflective barrier insulation features a reflective layer made of aluminum or another material, much as the name suggests. Radiant heat cannot accumulate where this insulation is installed since the radiant barrier reflects heat elsewhere, so the inside of your home stays cool.

This insulation goes over polyethylene bubbles or another type of substrate. If you live in a part of the country where it’s often warm, then insulating your floors, ceilings, unfinished walls, and attic with reflective barrier insulation is best. 

  • Rigid Foam Panels or Foam Board

All other types of insulation are assigned what’s known as an R-value, which defines the efficiency of your insulation in preventing conductive heat flow. The higher the R-value, the better.

Rigid foam panels and foam board have an R-value of around 4 or 6.5, which is good. Intended for floor or roof insulation (especially low-sloping roofs), rigid foam panels prevent heat from traveling through wall studs and wooden panels.

The insulation panels or boards themselves are polyisocyanurate, polystyrene, or polyurethane. Besides floors and roofs, you can also install foam board insulation on ceilings, foundational walls, and unfinished walls.

  • Blown-in Insulation

Although blown-in insulation appears soft like paper, if you touched it, you’d realize it has a texture akin to rock wool or glass. This insulation requires a machine for the application. Its R-value is 2.2 to 3.8, which is lower than rigid foam panel insulation by a decent margin.

Although it’s not the best type of insulation, you don’t have to use blow-in insulation on its own. You can spray it in areas where you haven’t been able to insulate otherwise or where regular insulation doesn’t fit.

  • Spray Foam Insulation

Similar to blown-in insulation, you squeeze out spray foam insulation to apply it to gaps, holes, and openings where air can leak through.

Most spray foam is liquid polyurethane and its cells can be dense or open. Open-cell insulation is the less expensive of the two, but its R-value is only 3.7 for every inch you apply. Closed-cell spray foam provides awesome insulation with an R-value of 6.2 per inch. It will cost more money up front, though.

You can use spray foam insulation for the same purposes as blown-in insulation, including for spots that you can’t easily access.

  • Blanket Batts

The last type of insulation is blanket batts. These long rolls may be made of plastic fiber, sheep’s wool, mineral wool, cotton, or fiberglass depending on where you buy yours. The batts go between the floor joists, rafters, and wall studs. You often have to slice down the batts to size, especially when working in constricted areas like an attic.

The R-value of blanket batt insulation is anywhere from 2.9 to 3.8 per inch, but some batts have an R-value as high as 4.3 per inch.

Air Sealing vs. Insulation: This Is the Better Choice for Energy Efficiency

photo of a technician using caulk to seal an air duct opening to reduce air leakage in a home
Using caulk to seal up that leaky air duct from the photo above. Air sealing is the first step toward a greener home, before insulation.

Both air sealing and insulation can make your home more energy-efficient since less air can escape and the air that’s within your home is more temperate. Yet between the two, air sealing is the better green measure.

It goes back to what we said in our post about blower door tests: “Insulation acts as a blanket over your own – but it doesn’t necessarily mean your home will have a tighter building envelope or be less leaky.”

Insulation is often likened to wearing a wool sweater. We think of it more like putting on an open-weave sweater and then stepping outside on a winter’s day. Sure, you have a sweater on, but the sweater has gaps that are letting air pass right through.

Air sealing can be installed in conjunction with insulation, but you want to start first with an energy audit and a blower door test. Then add the air sealing and insulation if necessary.

The Energy Star link we provided above calculated what your energy bill savings could be if your home has both insulation and air sealing. If you live in a southern state, here is the breakdown:

  • Climate zone CZ 1 – 7 percent on heating and cooling and 5 percent on the total house
  • Climate zone CZ 2 – 9 percent on heating and cooling and 6 percent on the total house
  • Climate zone CZ 3 – 14 percent on heating and cooling and 8 percent on the total house

For those who call a northern state home, here are your estimated savings:

  • Climate zone CZ 4 – 17 percent on heating and cooling and 12 percent on the total house
  • Climate zone CZ 4C – 20 percent on heating and cooling and 13 percent on the total house
  • Climate zone CZ 5 – 16 percent on heating and cooling and 12 percent on the total house
  • Climate zone CZ 6 – 18 percent on heating and cooling and 14 percent on the total house
  • Climate zone CZ 7 – 19 percent on heating and cooling and 15 percent on the total house
  • Climate zone CZ 8 – 18 percent on heating and cooling and 16 percent on the total house

That’s a national average of 15 percent for heating and cooling and 11 percent for the entire house. Depending on where in the country you live, those are some serious savings!

Conclusion

Between air sealing and insulation, the former will make your home more energy-efficient as you take care of leaks, gaps, and openings. Insulation can create a greener home too, and by combining the two methods, you could reduce your heating and cooling bills by around 15 percent!

Erin Shine

Erin Shine

Founder | Attainable Home

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