How do I know I have a duct leak? The old door trick....

Many times I have walked up to a customer's door, knocked , have the door open, and then either almost had my baseball hat blown off or felt like I was being sucked into a black hole.  What does this have to do with duct leaks you may ask??? Everything, including where the leak is.

Often times a leak is subtle or the home is large, so I use an infrared thermometer to shoot each vent.  I am looking for consistency with slight variation due to where the register is relative to the air handler.  Farther away from the air handler, I typically see a 2 to 3 degree rise in the supply air temp as it travels through the flex.  On a properly charged system I should see a 20 degree split between the supply air (at the register) and the return (at the air filter you hopefully change).  If I come across a grille that is way off, I'm looking at that one for a leak. 

This is where some attic work is required to inspect the flex attachment to the collar.  Often times the equivalent of a zip tie is used to attach the flex duct to the collar.  Over the years the heat, and especially Arizona attics (140 degrees or more), will break down the zip tie and they snap.  The supply air will be blowing all over the place except down the register.  A new zip  and you are back in business.

Return air leaks are a little tougher.  They can show up using manifold gauges (the hoses and gauges we use to check freon levels) but all that says is you have high pressures or a lot of heat in the system.  Many techs may misdiagnose this as overcharged (too much freon in the system) or go looking for dirty outdoor coils etc...  This is where the door check tells it all.

When you close up all the doors and windows in the house you have a decent seal.  Not perfect and you don't want perfect, you want your house to breath a little bit.  When you crack a door you will feel the airflow.  Which way is it blowing?

If the outdoor air is being sucked in you have a supply line leak and if the air blows out the door than your leak is in the return side.  Here is why.  The attic has louvers and openings in it so it can breath with the outdoor air.  If your return is leaking than the air handler is sucking in hot attic air (in unlimited supply with no resistance) across the coil and blowing into the home.  In a sense pressurizing the home.  The reverse in a supply or cold line leak.  The air handler is sucking in as much as it can because it now has not resistance on the supply side.  It can blow all day into the attic. 

So if your doors are a-whistling you may want to check out your duct work for any leakage.  Now you know which side of the duct is leaking before you climb in that attic.  For more tips and free A/C and Heat Pump DIY and troubleshooting help visit http://www.thermal-medics.com/.