Air Sealing

Homes burn through a mortifying 21% of the energy used in the United States. A  lot of that energy is spent heating and cooling your house. What worse? A whole lot of that energy is spent heating and cooling your backyard and front porch, through leaks and holes in your building envelope.  In fact, if you do some serious work sealing cracks, you can expect to net about $600.00 in annual energy savings. Sealing air leaks will garner most of us significantly greater savings than replacing windows, in part because the cost of materials and installation are much lower.

I. Overview:  Sealing up your home keeps more than air inside (it keeps cash inside, too).

Nothing personal, but the warm air in your house wants out. The silent (and costly) exodus of your warm air is made easier with the help of leaky doors, leaky windows and poorly sealed interior or exterior walls. Some of those holes and leakage points are visible to the untrained eye. The truth is, however, that even the draftiest old houses suffer most of their air leakage in places you don't see, due to the chimney effect, which we discuss in more detail below.  It's because of those hard-to-see leaks that we strongly recommend investing in an energy audit.  Some leaks require a home energy auditor's keen eye, structural know how and infrared technology, and others are just confoundingly hard to spot.  But first, we'll tell you a little bit about air sealing, why it's necessary, and how the flow of air works in your house.

II. Air Sealing Basics: Your money could be going up the chimney—even if you don’t have one.

Here's how the chimney (or stack) effect works: Cold air infiltrates your cellar through leaks and cracks in the foundation and walls, and begins rising. It works its way up through the floors and/or walls, then up into your attic through structural defects, holes in your ceiling, recessed lighting, leaky duct work, the furnace flue, the plumbing stack, a poorly insulated attic floor or improperly sealed areas in general. In some homes (even those that have no chimney at all), the chimney effect can be so pronounced that the effect is like leaving your front door open all winter long!

Something to Think About

It’s best to start your efforts to improve home energy efficiency with a home energy audit by a certified professional. You will find how much energy your home consumes and wastes, how you can best conserve energy, where the health and safety concerns in your house are, and estimate how long it will take you to solve the major issues. We have found out the hard way that a house is an interconnected ecosystem, and sometimes a complex one.  Learn what to take on first. You may well find out that you can keep your old windows and just seal up around the edges. You'll very likely come away with some attic and basement projects. Then again, you might find out you need a new roof….

While the chimney effect is the most common air leakage contributor, there are three other air leakage drivers you should be aware of: wind pressure, chimney/exhaust pressure and duct pressure.

1. Wind Pressure. (No, you don't have to live on a boat to care). Wind blowing against an exterior wall can push cold air into your home on the prevailing side and create negative pressure on the leeward side. The wind pushes air through holes and cracks in the windward wall, then exits through the leeward wall. Contributing factors include the exposure of your home, porch roof, inside corners and other features that trap the wind and surrounding vegetation. The end result is a cold and drafty home.

2. Chimney/exhaust pressure. Not to be confused with the chimney effect, chimney or exhaust pressure is created by active ventilation such as exhaust fans and clothes dryers. These fans can be so efficient at removing air that "make-up air" is drawn through holes or cracks in exterior walls or even down your chimney, creating a potentially dangerous condition known as backdrafting.

3. Duct Pressure. In homes with forced hot air heating systems, the furnace blows heated air out into living areas and is resupplied with air through a system of return ducts. If the return ducts system is leaky to the extent that the flow of air back to the furnace is restricted, it may double or triple air leakage through exterior walls compared to not using the furnace at all. It is essential to seal as many sources of duct leaks as possible to keep your energy costs low.

III: Take it on

Now that you know about some of the most common sources of air leakage, how can you tell which ones apply to your home? As always, we recommend starting with a home energy audit that includes a blower door test. The auditor will install a blower in one of your exterior doors, turn on a powerful fan that simulates an especially windy day and start depressurizing your home by creating suction. This will allow the technician to measure all of the sources of air leakage in your home. The audit will reveal air leakage in your home in terms of CFM (cubic feet per minute) or ACH (air changes per hour). The blower fan is so powerful that you can often feel air being drawn from the outside through cracks or holes in your walls. Ask to follow the technician around your home so he or she can point out and help you prioritize problem areas, critical information to have whether you plan on plugging the holes yourself or having a contractor take it on.

As you get started, turn to our air sealing buyer's guide to insure that you are using the right tools for the job.

The primary tools of the trade are expanding foams, non-expanding foams, caulk, insulation, and various types of weatherstripping. While caulking is widely available, it is definitely worth your time and money to invest in professionally rated materials that will keep cracks and holes properly sealed for years. Our advice: before stocking up on sealants and foams intent on sealing every last infiltration point in your home, take a few minutes to step back and look at the big picture. Check out our buyer's guide for more information about which sealing product makes the most sense for your needs.