Common Sources of Thermal Leaks in Your Home

Whether you’re a new homeowner jumping into house projects or you’ve been chipping away at your to-do list for years, you probably know there’s room for improvement in your home’s energy efficiency. Figuring out where your house is losing cooled or experiencing heat loss from your furnace and what to do about it can benefit your comfort, your budget, and the resale value of your home. 

Sealing thermal leaks is an ideal place to begin. 

In this short guide, we’ll cover common sources of thermal leaks—including those you can find yourself and those that a professional energy audit can reveal.1

#1 Old and Improperly Sealed Windows

No surprise here—windows are a common culprit of air loss. Older homes, in particular, may have windows that look lovely but perform very poorly. 

Is it possible your windows are the source of your steep energy bills? To find out, check for drafts and look for condensation on your window glass. 

Improvement options range from simple DIY to more comprehensive upgrades: 

  • Use blinds or heavy drapes to block the sun when you’re looking to cool down, or use dark-colored curtains to absorb sunlight in cold temperatures.
  • Add caulking and weatherstripping around windows for seasonal or long-term use.
  • Apply sun-blocking window film.
  • Upgrade to energy-efficient, low-emissivity windows.

Up to a third of your home’s energy leaks may come from windows and doors, so this is a great place to start.2

#2 Inefficient Doors

Wouldn’t it be nice if the only issue with doors was leaving them open or closed? As the largest intentional holes in your snug home, well-fit and well-constructed doors are critical to reducing unintentional airflow. Visually inspecting your doors and checking for drafts on a windy day is a good start to identifying a hidden leak. 

How can you improve the efficiency of your doors?

  • Caulk any openings or cracks in the door frame
  • Install door weatherstripping and gaskets
  • Sew or buy “door snake” draft stoppers 
  • Install new doors with higher energy efficiency
  • Seal windows if your door has one

As always, buying new is your most expensive option, but if you decide to replace a door, it’s a great opportunity to consider what visual and security upgrades can be part of this investment.

#3 Un- or Under-Insulated Walls

Yes, you see a solid surface when you look at your wall, but walls themselves can be a common source of thermal energy leakage. These energy leaks will be a bit more challenging to detect without knowing the construction details of your house or scheduling a professional energy audit. 

Walls can be problematic based on: 

  • The insulation level in your walls – Exterior walls should be fully insulated, but weak spots may connect walls to an attached home or garage. You can carefully investigate your insulation by way of electrical sockets—removing the cover and taking a look inside with a flashlight, or even pulling out some insulation to see what kind it is—but be sure to turn off your power first!3
  • Thermal bridging – This refers to the fact that your walls are not made of pure insulation—they include wooden framing and studs, which conduct heat flow more easily than insulation. Without being skilled in construction and knowing the nitty-gritty of your home’s building specs, ordering a thermal imaging report as part of a home inspection or home energy audit is your best bet.

There are not as many DIY approaches to wall improvement as with other thermal leak offenders, but adding awnings over metal windows and doors can provide some help. 

#4 Electrical Outlets

They’re small but mighty—and they add up. Having even a ⅛ inch gap around six outlets is equivalent to chopping a four-inch hole in roof leaks, and the average American home today has up to 70 electrical outlets.4

The fix for air leakage around outlets is pretty straightforward—plug up any gaps with caulk or foam. (You can also use foam gaskets designed for outlets, but caulking and foam will provide a superior seal.)

If you take on the project yourself, there are some critical things to remember when conducting an air leak test: 

  • Intumescent (fire-blocking) foam or caulk is best used around ceiling boxes.
  • Although generally not required by code, intumescent materials are a good idea for wall outlets as well.
  • You’re looking to seal up gaps outside of the box and where cables come into the box—never seal inside the electrical box. 

And, above all, turn off your power before working on any electrical project!

#5 Wide-Open Chimneys

Whether you like to enjoy the crackle of an occasional fire in your fireplace or you keep it full of decorative candles, your open chimney is more likely to be a full-time source of trouble in keeping the room at a comfortable temperature. 

The solution? A chimney balloon. Sounds like something from a children’s book, right? But a chimney balloon is pretty much what it sounds like: a filled bag placed in the chimney to block air from coming in or escaping. You can have one professionally installed or try a DIY version.5

Without taking measures to prevent air leakage, an open chimney can cause a heat leak or drain cooled air by up to 70%.6

#6 Air Ducts

Air ducts are the highways carrying heat or cool air to every room in your house. You want them to be secure, sealed, and insulated correctly to make sure they aren’t losing that heated or cooled air before it reaches its destination. 

The how-to principle of duct sealing isn’t complicated—what can make this a big job is the location of ducts and how difficult it may be to access them throughout your house. 

You may want to tackle part of the project on your own. Then, call in professionals for hard-to-reach surfaces inside of walls and ceilings and to perform a duck air leak test to confirm the leak detection is completed successfully.

To get started:

  • Check your visible ducts to ensure they are connected and free of holes or gaps.
  • Straighten or untangle any flexible parts that have become crushed or torn.
  • Use duct sealant (mastic) or metal-backed (foil) tape to patch any holes or leaks where the air is escaping.
  • Make sure connections where ducts vent into rooms are sealed well.
  • Add duct insulation to any ducts that go through unheated/uncooled areas of the building to prevent them from affecting the air traveling through them.

One (ironic) thing to remember is that you should not use duct tape for this project! Although strong, duct tape cannot withstand the temperature difference needed for this purpose.

Up to 30% of the heated or cooled air moving through ducts can be lost in a typical house due to leaks and improper connections.7 But at their most efficient, your air ducts will keep your home at the temperature you desire without wasting energy and driving up your utility bill in the delivery process. 

#7 Poor Attic Ventilation

Okay, “ventilation” seems like the opposite of what we’re trying to accomplish by sealing up leaks throughout your home, but some types of air exchange are necessary to keep your home properly heated or cooled. 

Heat rises, and attic spaces without proper ventilation can trap that hot air—which is not a good outcome, whether you’re fighting the summer temperatures or worried about ice dams in the northern cold. 

Your attic needs insulation baffles (or “rafter vents”) in addition to a layer of insulation covering the attic floor to establish the right mix of outdoor airflow without losing your perfect indoor temperature in the stories below.6 For more helpful tips like preparing an attic for cold weather, visit Attic Construction for more information. 

#8 Insufficient Insulation

We’ve already covered the insulation behind your walls, but insulation also plays an important role in your basement and attic. Let’s go over some common attic insulation mistakes.

Insulation is the partner that goes hand-in-hand with air sealing to reduce thermal leaks in your home. 

Determining whether your home could use new or additional insulation—and, if so, what kind—requires some help and research. There are different life expectancies and price points to consider, plus issues like moisture resistance and maintenance. (You can find out more about how insulation is rated (the “R value”) in our blog “What is Insulation R Value? Why is it Important?”)

But first, how do you determine your home’s current insulation status and needs?

An energy audit with thermal imaging, or infrared thermography (IRT), is an ideal thermal leak detector. You can purchase a thermal imaging camera or device, but an expert audit will include professional knowledge of what to scan and how to interpret the thermal image results from the thermal camera, often at a low cost. 

Reap the Benefits of Tackling Thermal Leaks With Attic Construction

Addressing thermal leaks with air sealing and proper insulation is a high priority for the health of your home and your family. Like any great investment, it will yield benefits based on what you put into it. These include:

  • Lower utility bills 
  • Better indoor air quality
  • Limited access for insects and other pests
  • Prevention of construction damage related to moisture problems
  • Improvement of your home’s resale value
  • Restoration of unpleasant drafts and overly hot or cold rooms and floors
  • Protection of your roof from winter ice dams 
  • Environment sustainability with a lower carbon footprint 

Ready to get started? Attic Construction is a well-trusted company that has been providing high-quality service since 2011. Whether you need San Diego, Orange County or Phoenix insulation installation, we can help. We offer a number of different insulation installation services that not only protect your home but also save you money in the long run. Questions regarding how an attic fan works? We’ve got you covered. 

Request an appointment to have one of our professional insulation installers come to your residence and do a complete attic inspection, with absolutely no strings attached. Get your free consultation today. Call today to get your hidden leak under control! 


  1. Energy Star Blog. Professional Home Energy Audits.
  2. Greener Ideal Blog. 5 Sources of Energy Leaks in Your Home.
  3. Energy Star Blog. What to Look For: DIY Checks and Inspections.
  4. Family Handyman Magazine. Foam Outlet Insulation Stops Cold Air Coming Through Electrical Outlets.
  5. EcoThrifty Living Blog. How to make a DIY chimney balloon.
  6. Architect Magazine. Where’s the Leak? 5 Common Ways Homes Lose Energy in Winter.
  7. Energy Star Blog. Duct Sealing.

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