If you are looking to cut down on your energy bills, air sealing your house is an excellent place to start. The furnace and air conditioner account for 43 percent of energy bills in the typical family home, so you can make a serious impact by ensuring that as much of that treated air as possible remains within your house, as opposed to leaking into the outdoors. Read on for tips on how to air seal your house and to learn the truth about myths regarding air sealing and moisture accumulation.
Why to Air Seal Your House
Your home is an enclosed space that you want to keep not too hot and not too cold. You want to keep the comfortable treated air (whether heated or cooled) inside your home while keeping the moist, cold (or hot) air outside. Unfortunately, not all existing homes are air sealed properly, making them drafty and less energy efficient. Cold drafts in your home are a symptom of the “stack effect.” If you feel a draft flowing through your house, that means that heated air is escaping higher up in the structure. Sealing off the cold draft will slow down the stack effect. Not only do leaks and drafts make your home less comfortable, they can cost you a bundle in energy bills.
How to Find Drafts and Air Seal the Home
To find drafts, wet the back of your hand and feel around doors and windows. Certain hand-held devices and even phone apps can also detect where and how cold air is entering your home (and where heat is escaping). Fortunately, sealing these leaks can be done by caulking around windows and doors or even stapling plastic sheeting over the outside of drafty old windows.
Hidden air leaks in attics, basements and around chimneys are typically bigger areas for heat loss. An often neglected place to look for drafts is at the mudsill and rim joists. These are the bottom pieces of your home’s framing where they meet the foundation. Newer homes have excellent sealing in this area, not so new buildings have moderate sealing, and older homes (pre-1950) have little to none. Leaks here can make your home’s basement cold and difficult to keep warm and dry. If your home only has a crawl space, leaks here can make your floors chilly and allow more moisture into your home. Encapsulating the crawl space with a plastic vapor barrier is a relatively simple procedure that can help alleviate these issues.
Sealing Up Drafts in the Attic
Another place to look for drafts and leaks is any place where plumbing or wiring passes through the wall outside or into your attic. Attics allow heated air to escape where wiring and plumbing emerges through holes from the living space. Seal all these gaps with expanding foam and caulk. Many recessed light fixtures mounted in your ceiling permit heated air to escape as well. Recessed lighting cans should be enclosed above the ceiling with wooden boxes to control the loss of heated air. Also be sure to put weather stripping on the door that leads into your attic to prevent heated air from sneaking out that way.
By sealing and blocking up leaks and drafts, you can save over 18 percent off your energy bill. While sealing up five or ten tiny leaks may not save you that much money, finding and sealing 50 to 70 will make a noticeable impact on your bill.
Don’t Forget to Air Seal Your Ductwork
The envelope of your house itself isn’t the only place to focus when looking for areas to air seal to save energy and money. Leaky ducts lose 20 to 30 percent of the air passing through them, which wastes energy and increases your electricity bill. Sealing your home’s ductwork is one way to ensure that your HVAC system is running at maximum efficiency.
Check the condition of your ductwork by searching for any loose connections or gaps. Also pay attention to areas where dust, dirt or mold can be pulled in then your ventilation system because this might also be making your family sick. Re-connect any loose or broken connections and seal these with UL-181 rated aluminum tape (DO NOT USE “duct tape” —it degrades within one to two years). For holes, gaps and seams, coat these with duct mastik or at the very least the aluminum tape. Mastik has the consistency of thick peanut butter and can be easily applied with a brush or a putty knife. Drying and curing time, however, is up to three days, so only apply mastic when you know you can leave your HVAC system off for that long.
The cold-air-return ducts are sometimes a forgotten part of the system. If your return ducts pass through or are open in a crawl space, make sure the crawl space has been encapsulated in order to better control temperature and humidity so that you can reduce the chance for mold or mildew entering your living space. You also want to seal all the return ductwork completely. Tightly sealed ductwork enables the blower fan to circulate air more effectively and efficiently throughout your home. Just like with air sealing your home, five or ten tiny leaks might not save you that much money, but sealing 20 to 50 sure will.
Debunking Myths About Air Sealing and Moisture
You may have come across claims that air sealing and insulation makes houses too tight, preventing homes from breathing. This energy efficiency myth came to life in part because of the passive solar/super-insulated homes designed in the 1970’s that wound up having severe moisture and mold problems.
Thanks to updated research into how the movement of air impacts the energy efficiency of a home, we now know that eliminating drafts, air sealing your home and installing the correct amount of insulation will go a long way to keeping moisture out of your home in the first place.
How Does Moisture Get in My Home?
All the water vapor in your home does need to be able get out. Moisture gets into houses in three main ways: air currents, diffusion through materials (including wood and concrete), and by heat transfer. Moisture gets in when it rains, from the ground underneath your home, and also from humans – we produce LOTS of water vapor just from the business of living (cooking, showering, and even just breathing). When moisture becomes trapped, like inside a wall for example, that’s when real problems arise.
The average relative humidity of a given climate varies in different areas of the country. Northern climes in winter have cold outside air hitting warm humid conditions inside the home, while southern climes in summer have hot, humid conditions outside and dry, air-conditioned interiors. Both scenarios can cause condensation problems. During wintertime conditions in dry climates, drafty homes tend to be drier inside, while in wetter climates, drafty homes will tend to feel dank and have more mold problems.
In most houses, water vapor exits by diffusing through the ceiling, entering the attic, and exiting through vents. There’s usually not enough relative humidity moving through the sheetrock to cause mold growth in attic insulation. Other exits include bathroom and kitchen ventilation fans.
Air Sealing Can Help Control Moisture
Air movement or drafts account for 98 percent of the water vapor entering your home, as it moves from high pressure or wetter areas to low pressure or drier areas along paths of least resistance. The better the attic is air sealed from the living space, the drier it is, and the less chance for humid air to build up in the attic and turn into a mold problem.
Apart from sealing against drafts getting into your home, look for places where water might enter your home, such as rain gutters or downspouts that leak into your basement. Make sure the downspouts carry water well away from your home. Look for water damaged siding, as well as windows and doors that don’t close properly. Be sure that bathroom and kitchen ventilation fans blow exhaust outside the home. Floor drain traps can also dry out and allow water vapor to enter your home that way. It’s a good idea in the winter to pour a little water into them once a month to keep the traps filled and sealed.
The Verdict on Air Sealing
For the modest cost of some foam, caulk and weather stripping, you can potentially capture an excellent return on investment from air sealing your home. Not only will air sealing save you money on your energy bills, it could save you from catastrophic repairs and bills related to mold or rot from moisture settling in your walls.