Ask the Engineer: Oh! To Breathe Again!

Summer storms on the evening of the 17th of June can sometimes bless you with a cool, breezy June 18th.  And what are you left with?  Slow moving clouds, grilling burgers that started their journey on a pasture on your Granddaddy’s farm, IPAs, a reclining lounge chair, and Avett Brothers.  You can never be sure if it was one of those Avett’s or the IPA that convinced you to put out some gnarled sawhorses, lay some old boards, and grab every eclectic chair in the homestead.   This is what we Southerners can only refer to as “supper.”  It’s a fine evening, real fine.

The air seems to have a crispness to it that makes you grateful to breath as the rays of light excuse themselves from the sweet day and go on to comfort other folks in lands you have yet to venture.  So why can’t your home have a taste of this freshness?  Well, friend, it can.  I can’t quite figure out why it isn’t done more often.  A commercial grade building is required, by code, to have fresh air introduced in multiples of the amount of people that are anticipated to adorn the doorways on a typical day.  Your single-family home does not have to account for this because there isn’t nearly the amount of folks and you’re going to introduce fresh air to the building envelop every time you open and close a door to enter or exit the home.

The conundrum enters into the equation when you turn on an exhaust fan in your home, over the stove or bathroom or shower (If I could interrupt, just a note, because I feel the general public should know what we in the industry call the fan over the toilet – a “fart fan”.)  This action of exhausting air from your house and distributing outside the home creates a vacuum in your space.  Your home is now at negative pressure in relation to all adjacent spaces, i.e. the outdoors.  So you and I know that your home isn’t sealed tight, and we know that the two systems will balance out; how then does your house make up the air?  It pulls it from the paths of least resentence: cracks and holes in your walls, ceiling, and floor.  This air isn’t conditioned; it’s hot, humid, summer air, or cold, dry winter air (or somewhere in between).

In the winter time, this isn’t necessarily a bad thing in South Carolina, but in the summer, coupled with, oh I don’t know, a thousand-year flood, you get opportunities for an uninvited guest – mold.

To fight this, all you need to do is have your HVAC guru install an outside air duct on the return side of your ductwork, just prior to entering your unit.  To get real fancy, have them install manual dampers on both your return and outside air duct so that you can balance the system.  You now are creating a positive house (good for moral? Just joshing), positive pressure that is.  This means unconditioned junk isn’t getting in and you are getting that fresh outside air in your lungs, at just the temperature you like!

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