We have had our share of warm days lately. So, when you come home in the middle of a very warm day, do find yourself asking “What is that smell?” It’s not the trash can in the kitchen, or your son’s smelly cleats, definitely not emanating from your pooch, but what is it? I’m assuming you have a programmable thermostat because you certainly have changed that out by now, right? And the thermostat is programmed to set itself back during the day while you are out, of course. With the thermostat set to give your AC system a little break while you are out, things have begun to get a little stale in your house, but where is that stale odor coming from exactly?
Probably your attic. In fact, run up there right now and see if the smell in your foyer matches the odor in your attic. What is happening is when you are away and your attic is cooking, heating up to temps in the triple digits for most of the day. I know you have always been told that heat rises and you figured that once that heat was in the attic it wasn’t going to defy gravity and descend into your house again, but you were wrong.
Instead of remembering that heat rises, remember instead that Hot Goes to Cold. Even with your AC set back a bit, it is still cooler in your house than it is in your attic. And I am assuming that you have numerous holes through your ceiling into your attic to allow the heat from up there to travel downwards (we call this holes in your building envelope). You may not have gaping holes in your drywall, but like 95% of homes built today, you have plenty of avenues for that hot air to travel.
Some of the larger holes are your pull down attic stairs, a large opening with no insulation and probably no weather stripping. Would you settle for a front door with no weather stripping? Of course not, it is the only thing between you and that unconditioned outdoors. Well what do you think your attic access is?
Another terrible source of leakage through your building envelope is can lights. Can lights now come in sealed units that prevent a lot of the air leakage that the older types cause, but most builders and homeowners don’t purchase the sealed units. Chances are yours are little chimneys just sucking that hot humid air back into your house. On a really warm day while the air is turned off, hold a lit piece of incense up under the can light and watch the smoke dance as the air pours into your house.
Duct work is also a big culprit. Ducts usually leak like crazy. As soon as the AC turns off, all those little cracks in your ductwork start exchanging all the cool air left in the ducts for that warm moist air in your attic. And then that warm air travels to every room in your house that has a supply register. That’s why you should have your duct system pressurized and tested for leaks. If you are getting a new HVAC system insist of having the ducts tested after the installation. If the installer can’t do the test himself, hire a Home Energy Auditor like me to come and run the test. It’s better to be sure especially since you just paid a tidy sum for that new system.
There are other holes as well like where the wire from your light switch travels up into the attic. Where those wires punch through to the attic are rarely sealed properly or at all and that is just one more path for hot air to travel down into your house bringing that lovely odor with it. Sealing up your building envelope is the only way to go. A little sealing up in the attic will do wonders. Then you can spend a whole lot less on trying to cover up that smell.