The short answer
Keep a Northern Virginia home at 30 to 50 percent humidity, and 30 to 40 percent in winter so the windows don’t sweat (ENERGY STAR‘s numbers). The fixes that work: let the AC run long enough to dry the air, set the thermostat fan to AUTO, seal leaky return ducts, and make sure the bath fans and dryer vent actually reach outside.
The part most people don’t know
Your family is a humidifier. A University of Missouri Extension guide says a family of four can add more than 6 gallons of water to the air in a day. NC State breaks it down: about 3 pints per person per day just from breathing, a pint for each meal cooked, and half a pint for each 5-minute shower.
That water has to go somewhere. In summer, the AC is supposed to pull it out. In winter it ends up on your coldest surface, usually the windows: window condensation in winter.
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Why a new AC can leave the house clammy
An AC only removes water while it runs long enough for the coil to get cold and drip. An oversized unit cools the air fast, hits the setpoint and shuts off before it has wrung much water out. A Department of Energy Building America fact sheet says short cycling in humid climates leads to poor humidity control, and cites a Florida study where units oversized by 50 percent or more used about 9 percent more cooling electricity a year.
Humidity also changes how warm a room feels. An NREL study found that at a common summer setting of 75°F, the temperature people actually feel can vary by 11°F. So a damp house feels warmer than the thermostat says, people turn it down, and they pay for the extra cooling.
The fan setting that undoes it
With the thermostat fan on ON, the blower keeps running across the wet coil after the AC shuts off, and water evaporates back into the house. In a Florida Solar Energy Center test, that cut the moisture removed by 44 percent compared with AUTO. Set it to AUTO for summer: fan ON or AUTO.
Leaky return ducts pull damp air in
Return ducts run under suction. If one leaks in a humid attic or crawlspace, it pulls that air in and sends it through the house. ENERGY STAR says 20 to 30 percent of the air moving through a typical home’s ducts is lost to leaks, holes and bad connections. More on leaky ducts.
Vents that don’t vent
A bath fan only helps if it goes outside. PNNL’s Building America guide says vent bath fans outdoors, never into the attic or crawlspace, and run the fan about an hour after a shower. If you don’t know where yours ends up, look in the attic. A duct that stops at the insulation just moves the water up a floor.
The dryer is the other one. A vent that’s crushed, disconnected or packed with lint can push warm, wet air into the laundry room or crawlspace instead of outside, and the Missouri guide’s number climbs to about 6.7 gallons a day with an unvented dryer. Our dryer vent cleaning is $199, normally $298, and it comes with a year of Comfort+ membership included. The year also covers a water heater flush with a sewer camera inspection, two heating and cooling maintenance visits and 15% off any service.
Why 50 percent is the line
University of Kentucky entomologists note that dust mites do poorly when relative humidity stays under 50 percent. One more reason to keep the house in the 30 to 50 range.
Get a hygrometer. It’s an inexpensive little gauge that reads indoor humidity, and it ends the guessing. If it reads high in summer with the AC running, one of the causes here is usually the reason.
When you need a dehumidifier
ENERGY STAR says a whole-home dehumidifier makes sense when a house stays over 55 percent consistently, and that ENERGY STAR models use about 20 percent less energy than standard ones. Check the AC, the fan setting and the returns first, because those are often the cause.
In winter it flips
Heated winter air gets dry, and the target drops to 30 to 40 percent to keep the windows clear. If yours reads under 30, see what a whole-house humidifier costs.
What we check
If the house feels damp with the AC running, our techs check the system’s size against the house, the fan setting, the condensate drain and the return ducts. If the returns are the question, our duct cleaning starts with camera photos of your ducts, free, so you can see what’s in there before you pay for anything. The cleaning is $598 instead of $798 for one system in a home up to 2,000 square feet.
A clogged condensate drain can also trip the safety float switch and shut the AC off. If yours stopped and a light is blinking, our error codes and warning lights guide covers what the blinks mean.
Book it
Book the dryer vent cleaning, call (703) 997-9757, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What humidity should my house be?
30 to 50 percent, per ENERGY STAR, and 30 to 40 percent in winter to keep the windows from sweating.
Why is my house so humid with the AC running?
Common reasons: the AC is oversized and shuts off before it removes much water, the thermostat fan is set to ON, return ducts leak damp attic or crawlspace air in, or the bath fans and dryer vent don’t reach outside.
Does running the AC fan on ON raise humidity?
Yes. Water on the cold coil evaporates back into the house when the AC cycles off. A Florida Solar Energy Center test found ON cut moisture removal 44 percent compared with AUTO.
Do I need a whole-house dehumidifier?
ENERGY STAR suggests one when a house stays over 55 percent consistently. Check the AC, the fan setting and the ducts first, since those are often the cause.
