Air sealing is one of the most important energy upgrades a home can receive, yet it’s also one of the most overlooked. Throughout Boulder, Golden, Westminster, Broomfield, and the surrounding Front Range, we regularly inspect homes where drafts, uneven temperatures, and high utility bills are caused by air leaks rather than a lack of insulation. Whether it’s an older home in Boulder or a newer home in Erie, sealing those leaks allows your insulation to perform the way it was designed.

If your house is drafty, if one room never gets comfortable, if your furnace runs constantly in January, there is a good chance the problem is not how much insulation you have. It is the air moving through it.

Insulation and Air Sealing Are Not the Same Thing

These get treated as one purchase and they solve different problems.

Insulation slows conductive heat transfer. Heat moves through solid material from warm to cold, and insulation puts resistance in its path. That is what an R-value measures.

Air sealing stops convective heat transfer. That is heat physically leaving your house by riding on air that moves out through gaps, and cold air moving in to replace it.

Insulation does almost nothing to stop air movement. Blown fiberglass in particular is air permeable by design. Air moves through it the way water moves through a sponge, and it carries your heated air with it.

Think of it as a sweater over an open window. The sweater is doing its job. The window is the problem. If you only buy the sweater, you have spent money on the half of the problem that was not costing you the most.

Where Houses Leak

Air leakage is rarely one big hole. It is dozens of small ones that add up, and they concentrate at the top and bottom of the house because of stack effect: warm air rises, escapes at the top, and pulls cold air in at the bottom to replace it. The whole house behaves like a chimney.

At the top

• Top plates, where interior walls meet the attic, usually open along their entire length
• Wire, pipe and duct penetrations
• Recessed can lights, many of which are open to the attic by design
• Bath and kitchen fans, and their housings
• Plumbing and mechanical chases running the full height of the house
• The attic hatch, which is usually a sheet of plywood with nothing on it
• Whole house fans, boxed in badly or not at all

At the bottom

• Rim joists around the perimeter of the floor system
• Crawl space vents and foundation penetrations
• Bare soil in an unsealed crawl space, which is an air path as well as a moisture path
• Sill plates and where the framing meets the foundation

How We Find the Leaks

We do not guess. We test.

Blower door testing depressurizes your house with a calibrated fan mounted in an exterior door, which exaggerates the pressure difference across the envelope and makes leaks measurable rather than theoretical. It produces a number for how leaky the house actually is, and it lets us find and rank the specific leaks instead of sealing whatever is easy to reach.

Combustion appliance zone testing, or CAZ testing, checks that your furnace, water heater and any other combustion appliances are venting correctly. This matters more than most homeowners realize. Tightening a house without checking combustion safety can cause a naturally drafting appliance to backdraft, pulling combustion gases into the living space instead of up the flue. A contractor who air seals without CAZ testing is taking a risk with your house that they have not told you about.

We perform blower door and CAZ testing in house with our own equipment and our own certified staff. Three certified BPI analysts are on our payroll. Most insulation companies in this market subcontract this work or skip it entirely.

Sequence Is Everything

Air sealing happens before insulation, every time, without exception.

Once loose fill material goes down, the top plates and penetrations underneath it are buried. Sealing them afterward means moving or removing the insulation you just paid for. Crews that skip air sealing are not making a judgment call about your house. They are saving two to four hours and hoping you never find out.

This is the entire reason a cheap attic bid and a complete attic scope produce different results from what looks like the same product. Same material, same depth, different sequence, and the performance is not close.

What Air Sealing Does Not Fix

Worth saying plainly, because you should not buy this expecting the wrong outcome.

Air sealing will not fix a failed furnace, undersized ductwork, or a room that has no supply register. It will not compensate for single pane windows on its own, though it usually matters more than the windows do. And a house can be sealed too tight without adequate ventilation, which is why testing and a ventilation strategy are part of the work rather than an afterthought.

What it will do is make your insulation perform the way its R-value claims, even out the temperature between floors, cut drafts, and reduce how hard your heating system has to work to hold a setpoint.

Air sealing is part of every attic and crawl space scope we write. If you want to understand what your house is actually doing before you spend money on it, that is the conversation to have. Whether you’re dealing with uncomfortable rooms in Boulder, drafts in Golden, or rising heating costs in Westminster, we’ll identify where your home is leaking air and recommend the right solution for you.

Why Choose Koala Insulation of Boulder

CCEF Approved Contractor

Koala Insulation of Boulder is an approved contractor with the Colorado Clean Energy Fund. That means our customers can finance insulation work through RENU loans and ClearPath On-Bill financing, with terms built specifically for energy efficiency improvements rather than a generic home improvement loan.

Not every insulation contractor in Colorado carries this approval. Ask us about it on your estimate, and we will walk you through what you qualify for.

Limited Lifetime Warranty

Our work carries a limited lifetime warranty. In practice, it is simpler than that sounds. If we did the work on your home and something is not right, you call us, and we come back and fix it. No claim forms, no argument about what is covered.

Three Certified BPI Analysts on Staff

The Building Performance Institute certifies professionals to assess how a home performs as a complete system: air leakage, insulation, ventilation, moisture, and combustion safety. Most insulation companies do not employ a single certified analyst. We have three.

It is the difference between someone who can install insulation and someone who can tell you why your house is uncomfortable in the first place.