Leaky homes are hard to heat and hard to cool. The only way to know whether your home is leaky or tight is to measure its air leakage rate with a blower door. A blower door is a tool that depressurizes a house; this depressurization exaggerates the home’s air leaks, making the leaks easier to measure and locate.
An energy-efficient house must be as airtight as possible. Many older U.S. homes are so leaky that a third to a half of the home’s heat loss comes from air leaks.
There is no such thing as a house that is too tight. However, it’s also true that there is no such a thing as an airtight house. Every house leaks, and that’s why we perform blower-door tests — to measure a building’s leakage rate.

Home Comfort provides Insulation Assessment, Installation & Servicing for Bloomington-NormalCantonGalesburgLaSalle-PeruMacombOttawaPekinPeoria and Washington – plus the surrounding areas.


Who needs a blower door?

Blower-door testing is useful for both new construction and existing homes. By testing a new home, a builder:

  • Can determine whether a certain airtightness target has been met;
  • Can document airtightness levels needed to qualify for certain home labeling programs, including Energy Star and Passivhaus;
  • Can do a better job calculating heat loss and heat gain the next time he or she builds a similar house;
  • The homes airtightness is a selling point to prospective homebuyers.

If you’re building a new home, the best time to conduct a blower-door test is after the home is insulated and drywall is hung.


Testing existing homes

There are at least two reasons to conduct a blower-door test on an existing house: to determine how leaky it is, and to help locate and fix the leaks.
When a blower door is used to help an air-sealing contractor locate and fix leaks in an existing house, the procedure is called “blower-door-directed air sealing.”
(To see a Green Building Association video of blower-door-directed air sealing, click here.)


Interpreting your results

There are two main ways that blower-door tests are reported: airflow at a pressure difference of 50 Pascals (cfm50) or air changes per hour at a pressure difference of 50 Pascals (ach50).
The first number — cfm50 — can be read directly off the airflow manometer at the time of the test.
The second number — ach50 — can only be calculated once the building’s volume has been determined. To calculate ach50, multiply cfm50 by 60 minutes per hour and divide the product by the building volume, including the basement, measured in cubic feet.
Some blower-door technicians estimate a home’s “natural infiltration” or “natural air change rate” (ACHnat). This number shouldn’t be taken too seriously, since it is only an estimate. Natural infiltration rates (and rules of thumb for calculating ACHnat) vary by climate. In Minnesota, ACHnat approximately equals ach50 divided by 17, while in Florida, ACHnat approximately equals ach50 divided by 30. According to Gary Nelson, the president of The Energy Conservatory in Minneapolis, “ACHnat is probably only accurate plus or minus a factor of two.”


Is my house tight?

Here are some comparison points to help interpret an ach50 reading:

  • A 2002 study of 24 new Wisconsin homes showed a median air leakage of 3.9 ach50.
  • New home builders in Minnesota routinely achieve 2.5 ach50.
  • The Canadian R-2000 program has an airtightness standard of 1.5 ach50.
  • The Passivhaus airtightness standard — a tough standard to achieve — is 0.6 ach50.

David Keefe, the manager of training services for Vermont Energy Investment Corporation, recently wrote an article on blower-door testing. “Houses with less than 5 or 6 ach50 are considered tight, and those over 20 are quite leaky, though these numbers can be misleading without considering other variables such as climate, house size, and old versus new construction,” Keefe wrote. “Tight houses tend to measure less than 1,200 cfm50, and moderately leaky homes measure between 1,500 and 2,500 cfm50. Homes that measure over 3,000 cfm50 are considered leaky.”
According to The Homeowner’s Guide to Renewable Energy by Dan Chiras, “A really good measurement is around 500 to 1,500 cfm50. The older houses we work on typically fall in the 6,500 to 8,500 cfm50 range.”


Blower-door-directed air sealing

Any competent energy audit of an existing home must include a blower-door test. Once you know your air leakage rate, you can formulate a plan for improving your home’s performance.
The leakier a home, the more economic sense it makes to hire an air-sealing contractor. “Homes with more than 6,000 cfm50 may merit days of labor and hundreds of dollars of materials,” write energy experts John Krigger and Chris Dorsi in their book, Residential Energy. “Homes with 1,500 cfm50 are difficult to improve.”
If your house is leaky enough to justify air-sealing work, you’ll need a blower door to efficiently locate and fix the leaks. Blower-door-directed air sealing is done while the house is depressurized to about 30 Pascals.
Once the blower-door has been set up, it usually makes sense to leave the fan running for several hours. By walking from room to room, many leaks can be found by feeling around with your bare hands. Subtler leaks can often be found using a smoke pencil or smoke bottle. In cold weather, an infrared camera can also be used to find air leaks.
The most important areas to seal air leaks are down low — in the home’s basement or crawl space — and up high — at the attic floor. Because of the stack effect, leaks in these areas matter much more than leaks in the middle of the house, where there isn’t as much of a difference in air pressure between the indoors and outdoors.
Many homeowners assume that gaps around windows and doors are responsible for most of a home’s air leaks. In fact, air leaks in the following areas are usually much more significant:

  • Basement rim joist areas;
  • Holes cut for plumbing traps under tubs and showers;
  • Cracks between finish flooring and baseboards;
  • Utility chases;
  • Plumbing vent pipe penetrations;
  • Kitchen soffits;
  • Fireplace surrounds;
  • Recessed can lights; and
  • Cracks between partition top plates and drywall.

With the blower door running, air-sealing work begins, using a variety of materials, including spray foam, caulk, and rigid foam board. Workers first attack the largest and most obvious leaks. As they proceed, they periodically check the blower-door fan’s air flow to determine whether the air-sealing work is effective.


Don’t forget a pre- AND post- combustion safety check

Before and after air-sealing work in an existing house is complete, it’s vitally important to conduct a combustion safety test. This usually involves a worst-case depressurization test: all of the home’s exhaust fans, including the clothes dryer, are turned on at once, and every combustion appliance is checked to be sure there is no spillage of flue gas into the home.
Sealed-combustion appliances are immune to spillage and therefore preferred for tight homes.
Air-sealing contractors need to have a good understanding of “house as a system” principles to be sure that their work doesn’t cause or exacerbate indoor humidity problems, radon exposure, or a variety of other potentially hazardous conditions.


Do you need mechanical ventilation?

Many air-sealing contractors aim to lower the air-leakage rate in an existing home to somewhere in the range of 1,000 to 2,000 cfm50. If air-sealing work continues until the house is tightened below 1,000 cfm50, it’s advisable to install a whole-house mechanical ventilation system.
So why would anyone want to first tighten a house and then turn around and ventilate it with a fan? For several reasons:

  • Leaky homes don’t provide dependable volumes of fresh air. In a leaky house, air infiltration rates are very high in some conditions (when it’s cold outdoors and when it’s windy) and very low in other conditions (when outdoor temperatures are mild and there is little wind.)
  • Leaky houses tend to be over-ventilated in zones that are leaky and under-ventilated in zones that are relatively tight.
  • Air leakage through wall and ceiling assemblies can lead to condensation, mold, and rot.
  • Leaky homes are uncomfortable.
  • Tight homes use less energy than leaky homes — even taking into account the electrical energy used for ventilation.


An energy audit is a painless process that will detail all the areas of your home that can be improved for energy efficiency. Our energy team will assess your homes structural design, insulation, electrical system, HVAC system and all other integrated systems that you may have. We will run equipment in your house such as blower doors, combustion analyzers, and CO monitoring systems. These are just a few of the tools that assist our energy team in seeing your “house as a system” and diagnose issues in their entirety. With results from these types of tools we will prepare a report that will document all areas with rooms for improvement with documentation showing why this recommendation was made. Call us to schedule your home audit today!


For New Home Construction.

Each revision of the International codes tends to ratchet up energy performance requirements, and the 2012 revision is no exception. Although its adoption may be a long ways off in some jurisdictions — after all, many rural areas of the U.S. still have no building codes at all — the 2012 International codes became law statewide in Illinois January 1, 2013.
What’s new?
The 2012 code requires more insulation, a tighter building envelope, increased duct sealing, better windows, and more efficient lighting than the 2009 code.
Here is a summary of the important changes for residential builders in the 2012 International codes:
Duct tightness requirements have become more stringent.
Blower-door testing requirements have become MANDATORY and more stringent; the 2009 maximum of 7 ach50 has been changed to 5 ach50 for our climate zone #2.
Some homes in zone #2, will be required to have a whole-house mechanical ventilation system.
Insulation R-values have increased in attics to a minimum of an R-49.
Basement walls must be insulated to an R-15 continuous or an R-19 batt if framed.


A short history of the blower door

During the 1960s, energy experts didn’t realize the extent to which air leakage contributed to residential heat loss. During the early 1970s, however, a few researchers in Sweden, Saskatchewan, and New Jersey began studying air leakage in homes. In spite of these efforts, most early airtightness researchers still didn’t understand how air was leaking out of most existing homes.
The Eureka moment came in 1977. A Princeton University researcher named Gautam Dutt was frustrated because he couldn’t account for all of the heat escaping from a group of townhouses he was studying in Twin Rivers, New Jersey. According to a July 22, 1979 New York Times article, “Of 30 or so houses he [Dutt] checked, all were losing three to seven times as much heat to the outside as the models predicted.” After Dutt spent hours investigating the homes’ nooks and crannies, he eventually pulled back some attic insulation and discovered a huge air leak through an unsealed utility chase. Dutt is now credited as the discoverer of the “thermal bypass.”
The blower door was originally a research tool. It was simultaneously and independently invented in the early 1970s by two groups of North American researchers — the so-called “Princeton House Doctors” (David Harje, Ken Gadsby, Frank Sinden, and Dutt) in New Jersey and a group in Saskatchewan that included Harold Orr. The first commercially available unit, the Gadsco blower door, hit the market in 1980.
In 1981, Harry Sherman and his son Max — Max is now a senior researcher at the Lawrence Berkeley National Laboratory — started selling blower doors under the Harmax brand. A year later, Gary Nelson, the founder of The Energy Conservatory, started selling the Minneapolis blower door. Of these three pioneer companies, only The Energy Conservatory is still in business.