Can my home be depressurized? What does that mean? Why?

This entry is part 3 of 5 in the series Why is it so expensive?



Usually homeowners only hear about pressure changes in their home when talking about balancing their heating and air systems.   While it is not common to hear about it with respect to home energy efficiency it should be.  A de/pressurized home can not only be expensive but it can also directly impact your indoor air quality.

If more air is entering a home than is leaving it has positive pressure or it is pressurized.   If more air is leaving the home than is entering the home has a negative pressure or is depressurized.   The same can be said for any room in your home.  In reality, each room can behave differently and this can also affect your costs as well as indoor air quality.

Previously, I posted a discussion about natural and mechanical ventilation and that plays into pressure changes as well.   A home’s pressure changes are directly linked to the seal of the home.   Essentially, the tighter the seal the less vulnerable a home is to outdoor pressure changes via natural ventilation.   The more balanced the ventilation system the less vulnerable a home is to pressure changes via mechanical ventilation.

Think about a home that has neutral pressure.  That is pressure from outside is the same as pressure from the inside but with the windows and doors closed.  If you turn on the bathroom fans or the dryer then that would create a negative pressure of the home.  These appliances will force air out of the home.   In this situation the home will draw air from anywhere it can.  Usually the natural ventilation of all those crooks and crannies throughout the home provides ample source of infiltrating air.

Obviously, the tighter the seal of the home the more difficult it is for the home to draw that air from the outside.  Just to be clear.  Most homes are not that tight.  In fact, if you were that tight you probably invested, had an energy efficiency renovation company get your house to that standard, and bragged about it to everyone.   Sorry, you didn’t just get there on your own.

Now think about this same scenario in the summer time.  Your thermostat is set to 78 degrees and the unit is currently off and you are comfortable.   The fans and dryer come on pushing that conditioned air out and that negative pressure pulls the outdoor air back into your home.   You expected that your AC unit would come back on eventually.  However, this negative pressure is going to accelerate the unit coming back on.   It is the same scenario for winter time.

This is an easy scenario to think thru and it sounds manageable.  However, there are several other drivers that cause pressure changes.

What can I do to minimize my vulnerability?

1)  Get an energy audit today to locate those crooks and crannies and understand how big they are.  I promise you they are much bigger than you think.

2)  Fix the biggest crooks and crannies.  You can’t get them all but you can definitely make a big dent that pays back the cost quickly.

3) Pay attention to how often your heating and air units come on and how long they stay on.   Chances are there is a rhythm.   An energy monitor can do this easy for you.   It can also help you compare before and after rhythms for your fixes so you can measure and confirm the changes.

Let me know if this helps or if you have a question.

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