Unintended Consequences

Linda and I were having a serious conversation the other day. (Actually, she was having the serious conversation.  I was just being me.) 

Anyway, I was explaining how a house is a complex, dynamic, integrated collection of systems.  When you shut the door or go on vacation, your house does not go into stasis.  It does not go to sleep.  The water pressure goes up and down.  There can be electrical power surges.  Wind, rain and heat put pressure on the house.  Concrete continues to shrink and crack over the course of its' life.  And, when you change something in a house, it may affect another system.  There may be unintended consequences. 

So, listen in to the rest of our conversation......

"Would you like an example?"

"Sure."

"OK. Did you know that changing your carpet can affect your heating and cooling?"

Her eyes squinted up a little.  She leaned forward. (Actually, I think she looks at me that way a lot.)

"Sure."

"The space at the bottom of the door let's the air you put into the room get back to the return.  So, when you put in that new thick carpet, you fill up that space. When you shut the door, you block the return air.  You've created positive pressure in the room and negative pressure in the rest of the house.

Partially close the door, leaving it open an inch or two.  Turn the fan on.  Door shuts on its' own?"

Still squinting, she leans in some more and says...

"We just had new carpets installed in the house.  The doors shut on their own.  My husband thinks the house is settling.  What's it all mean?"

"Well, since air can't get out of the room, air can't get into the room. Essentially, no heating or cooling.  And, since the system is looking for return air, it will get it from the kitchen, laundry or bathroom vents.  Or, through the walls, from the attic, lots of places.  When you start mixing unconditioned air with conditioned air you reduce the efficiency.  Work with your HVAC technician to decide if you should trim the doors, use flexible duct to connect the room to the hallway through the attic or ceiling to re-establish the return air or do nothing."

She sat back.

"Dang!"  (Actually, she said an Anglo-Saxon love oriented action verb.)

So folks, keep in mind that your home is a complex, dynamic, integrated collection of systems.  When you change something there may be unintended consequences.

Nel Broce

Nel is a Senior Inspector at Desert State Home Inspections. ASHI certification #109712, AZ certification #38548. He can be reached at 480-585-6456.