Feeling muggy indoors: Part II

By Hannah McKenzie
Feeling muggy indoors: Part II

A whole house dehumidifier unit attached to or separate from the HVAC duct system and properly calibrated is often a good option.

Q: My house occasionally feels uncomfortably humid. Would a stand-alone dehumidifier be a good way to fix this problem?

A: When your house feels muggy, as mentioned in last month's article, it is best to start by finding and controlling the sources. It can be as simple as using an exhaust fan when you shower or as cumbersome as sealing ductwork.

Most homes have at least one unofficial dehumidifier — the air conditioner. Inside the air conditioner, air is cooled to dew point — around 55 degrees — so most of the water vapor in the air is removed by changing from vapor to liquid. (This is the same process that leaves dew on the ground in the morning.) Once the air is chilled and releases water vapor, the cooled air is then blown into the rooms of your house while the liquid is drained outside.

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Your air conditioning system also performs as a dehumidifier.

Typically, homes are the least humid when the air conditioner runs for long stretches of time — like during a 90-degree day — because all of the inside air is repeatedly pulled through the system and dehumidified.

On the flipside, if it is 90 degrees outside and the air conditioner runs for short bits of time hitting the desired temperature in a jiffy, the HVAC unit is oversized and will not dehumidify the house adequately. That may be why you are sweaty even when the thermostat is set to 76 degrees. It is common to find oversized air conditioning systems now that homes are insulated and air-sealed better than ever. Ideally, HVAC contractors will recommend a correctly sized HVAC system by doing an in-depth "load calculation" that uses information about your home, such as geographic location, foundation type, insulation levels, windows, house air tightness, and duct air tightness, just to name a few.

Regardless of your air conditioner's size, the spring, fall and cool summer nights in North Carolina are times when our homes feel muggy. Some folks love hearing the nighttime chirps of bugs and frogs through open windows. A ceiling fan and seersucker sheets may be enough for their comfort. If you are plagued by allergies or other health challenges, shutting the windows and improving your home's HVAC system may be your ticket to drier air.

Selecting a knowledgeable HVAC contractor is important. Get recommendations from friends and neighbors who have solved similar problems. Ask for at least 10 references and contact a handful of them to ensure that the company communicates well with their customers, is prompt, respects customer's homes, and truly improves comfort.

If you decide against expensive adjustments to your HVAC system, a stand-alone dehumidifier could be an adequate solution. Stick with an Energy Star-labeled product to ensure quality and energy efficiency. Be diligent about emptying the drain pan and consider the annual operating costs in addition to the unit cost.

About the Author

Hannah McKenzie is a residential building science consultant at Advanced Energy in Raleigh who specializes in working with nonprofit developers like Habitat for Humanity to make new affordable housing energy efficient.

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