Could air infiltration be sucking money from your wallet?

Posted by Grant Bowman on March 14, 2017

Very young girl going outside while holding open a glass door.

Air infiltration is a natural occurrence. Differences in air temperature and pressures are always at work trying to even out the pressure between the inside and outside of your home.

Every time you open a door to enter or exit, you are allowing heated/cooled air to leave the house and cold dry/hot sticky air to enter. That movement of air will cost you electricity and heating fuel to recondition that air. We all need to enter and exit our home, so this is an acceptable cost of living. But all the other openings in the envelope of our house are things we can work to control and thus save some of our hard-earned cash.

There are two main areas where passive air movements occur in the building envelope:

  • Around any opening in the exterior wall or ceiling surface
    • Windows and doors
    • Electrical outlets/cable connections
    • Supply and return ductwork that originates from the attic or an unconditioned space
    • Dryer vents or kitchen exhaust venting
    • Gas service entry
    • Electrical service entry
    • Plus, many more
  • Chimneys and ventilation systems
    • Chimney for natural venting water heaters/furnace (Class B)
    • Chimney for wood fireplace or pellet stoves (Class A)
    • Kitchen hoods and bath exhaust fans
    • Ductwork located in unconditioned spaces (leaky ducts)

How we go about fixing problems in our building envelope will vary depending on what kind of leak it is. If the leak is a break in the continuous vapor barrier of our building envelope, then some sort of caulk or crack filler/sealant will do the job as long as it is rated for moisture or UV exposure. Walk around the exterior of your home and look for any opening or gaps around any piping/venting/trim boards.

Where there are fixtures like ceiling lights or wall outlets, you may need to be a bit more creative about how you go about sealing the openings into the wall or ceiling. Work safely and turn off the power before working inside any electrical boxes of any sort.

Bath fans and kitchen exhaust fans, make sure the in-line dampers are working to cut down on the amount of air that will freely move through the duct system while it is not in use. Make sure that the intake screens on any combustion air intakes or air exchanger vent terminations are clear of lint and debris.

Any ductwork for heating/air conditioning/ventilation that is outside of the building envelope will cause some air infiltration. How much will depend upon how well it was installed originally and how well it has been maintained. Any joint between ducts that is not sealed will leak, along with any flex piping that has punchers or loose taped joints.Man shining a flashlight into an air duct.

If you have a return duct that runs in the attic and it leaks, it will be pulling in HOT/HUMID air in the summer or COLD air in the winter. Both of which will increase the cost you pay to cool or heat your home. The same can be said if the ductwork is in a cold unconditioned basement or crawl space.

Sealing ductwork is time consuming, but it will be worth it if you have access to it and do it well. Just remember, if you seal it, you will cause any leaks you miss to leak even more. You may want your heating specialist to verify the duct statics and add more return if your system is already working too hard and you just took all the leaks away.

Another point we touched on earlier was chimneys. Any heating appliance that uses indoor air for combustion is removing conditioned air from the house, sending it up the chimney. Building codes require that adequate combustion air is added to the close proximity of the appliance(s). This air can be COLD and make your floor in the area cold also. You may want to think about newer appliances that have their own combustion air piped directly into the appliance. This is normally called a two-pipe combustion system or sealed combustion, it will not affect the pressure balance within your building envelope and save you money and comfort over the long term.

Infiltration is a huge subject and can be influenced by so many conditions. Some are natural and many are from poor installation practices. Take some time to look over your house, get some opinions from people who specialize in this area. Get some quotes on what it will cost to have the major deficiencies repaired. You may need to do it in steps, depending on the age and condition of your home, just keep at it and before you know it you will have a nice, tight and comfortable home.  

Grant Bowman

Grant Bowman

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