Have you ever awakened in the middle of the night, sweating in your air-conditioned house? Do you then have to keep lowering the thermostat setting to colder and colder temperatures to be comfortable?

Did you buy a new high-efficiency air conditioner, but didn’t save what you expected on your electric bills? Or have you found that the new system doesn’t keep you as comfortable as the old one did?

Do any family members suffer from allergies or asthma? Do you ever smell moldy or musty odors when you come in from outside? Have you noticed mold growing anywhere in your house — on your AC vents, for instance?

If you answered “yes” to any of these questions, your home might be suffering from a widespread, invisible, and, until recently, poorly understood problem: excessive indoor humidity. It is a growing problem, and surprisingly, the use of modern, higher-efficiency air conditioning systems is making it worse!

Information is the key to determining if your home has humidity problems, and how to solve those problems or prevent them when investing in a new cooling system. This report will explain what you should know before talking to an AC contractor, and it will highlight some little-known facts about air conditioning. Unfortunately, even most contractors are not aware of this important new information!

New Air Conditioners Can Contribute to Mold Growth in Homes

The Comfort Institute in Washington is warning that some new high-efficiency air conditioners can contribute to unhealthy mold growth in homes.

“The new units do often cut cooling bills by 30% to 50%,” says researcher Brendan Reid. “However, there’s often a hidden cost to health and comfort. Many new air conditioners simply don’t remove the humidity the old ones did. It is possible to save energy and remove humidity at the same time, but usually not by simply swapping out the equipment.”

Controlling indoor moisture and humidity is the key to controlling mold. The American Lung Association, the American Medical Association, the Environmental Protection Agency, the Centers For Disease Control, and many other authorities recommend keeping the relative humidity level in your home between 30% and 50% year-round.

What happens when humidity levels climb higher than that? Check out this infographic for a few common consequences.

There’s More to Comfort Than Air Temperature

According to Reid, comfort also suffers when an air conditioner can’t effectively control indoor humidity.

“Many people find that they aren’t comfortable at various times of the day or cooling season, and don’t know why,” he says. “For example, they might wake up early in the morning covered with sweat. What’s happening is their air conditioner is controlling temperature, but the indoor humidity is bouncing up and down, typically from 45% to 75%.

“There’s a lot more to being comfortable than just air temperature. When indoor humidity levels are too high, our skin can’t evaporate moisture as well.”

The Comfort Institute has recorded unhealthy relative humidity levels of over 80% in some homes with new air conditioning systems.

Can You Save 50% on Your Utility Bills with a High-Efficiency Air Conditioner?

Many homeowners who have invested in new high-efficiency heating and cooling equipment didn’t get the comfort and energy efficiency they paid for.

There are many reasons for that. A key one is that many homeowners find they have to change their preferred thermostat settings after putting in a new system.

If faced with a cool but clammy house, many people try to achieve comfort by further lowering the thermostat, so that their air conditioner runs longer. According to Reid: “This can help, but it’s no fun to have to be constantly playing with the thermostat to compensate. Another big problem is that the colder you try to keep the house, the more the air conditioner has to run, compared to when the older unit was doing the job at a higher setting. This eats up a lot of the energy savings that the new unit was supposed to deliver.”

A Florida university research study found that for every degree homeowners lower their thermostat setting, it increases air conditioner use by 10%. Colder settings also lead to increased surface condensation and mold growth.

The Comfort Institute offers the following tips to ensure your new air conditioning system can control indoor humidity, keep mold at bay, and save money on utility bills:

  • Ensure your system is the right size. “When it comes to air conditioning,” says Reid, “bigger is not better. An oversized unit will quickly cool the house and then shut off before it does the longer job of removing humidity.” The Comfort Institute, as well as the Department of Energy, US EPA, and electrical utilities nationwide, recommend having us perform a computerized equipment sizing calculation conforming to the industry standard “Manual J.”
  • Consider an air conditioner with enhanced dehumidification features. Not all systems are the same regarding moisture removal. Ask for a unit with a TXV valve, and be sure the contractor doesn’t intentionally pick an excessively large indoor evaporator coil just to claim a higher SEER rating. “Some units have advanced humidity sensing controls, variable speed fans, or two-speed compressors that help wring out more moisture,” explains Reid. “Unfortunately, the air in these systems runs much colder, which can lead to excessive “sweating” on ducts and equipment located in attics or crawl spaces.”
  • Consider investing in a high-capacity ducted dehumidifier. Even the best AC unit can’t keep the house dry and comfortable during cloudy or rainy weather. There are now high-efficiency, high-capacity dehumidifiers available that supplement the air conditioning system. They can be installed out of sight using ductwork, and connected to a condensate drain so that you never have to empty the reservoir. This equipment dehumidifies the whole house and also cleans the air 24 hours a day, 365 days a year. Some models even provide filtered fresh outdoor ventilation air.
  • Install and use quiet, effective bathroom exhaust fans when bathing. Exhaust the steam before it humidifies the rest of the house.
  • Install high-efficiency air filters and regularly clean the indoor coil and drain pan. Having a contractor perform this service is essential to control mold growth in the duct system.
  • Have your house and duct system tested for excessive air leaks and have them sealed. “In much of the country, for most of the spring, summer, and fall, the primary source of moisture is the outdoor air leaking into the house. It contains very high levels of humidity in the form of invisible water vapor,” explains Reid. “While some outside air is necessary, too much raises summertime indoor humidity to unhealthy levels and can overcome the dehumidification capacity of the air conditioner. The worst air leaks are usually in the heating and cooling duct system. The new AC systems are much more affected by duct leaks than the old equipment.”
  • Have your home tested using a new computerized diagnostic instrument that measures air leakage. “The Infiltrometer blower door test typically takes an hour to perform,” says Reid. “The result is an exact measurement of the home and duct system air-tightness. Some houses are very airtight and need improved ventilation. On the other hand, most are too leaky. This usually causes excessive summer humidity, dry air and cold drafts in winter, uncomfortable rooms, excessive dust, and high heating and cooling bills. Until you test, you just don’t know.”

More on the Infiltrometer Test

The Infiltrometer test instrument was originally invented by the Department of Energy scientists. It has been featured in National Geographic magazine, Popular Science, and on This Old House and other TV shows. Many heating and air conditioning contractors offer the test as part of a “Whole House Health and Comfort Checkup” that also checks insulation levels and overall duct system performance.

Some air leaks can also bring in contaminated air. Building scientists have recently discovered that in the typical home, well over half the incoming air first passes through the attached garage, crawl space, basement, or attic, where air becomes polluted by several different sources. These include:

  • Mold spores
  • Moisture
  • Insulation fibers
  • Carbon monoxide
  • Automobile exhaust
  • Radon gas
  • Volatile organic chemicals

All of these contaminants can negatively impact your family’s health and safety. The Infiltrometer test aims to solve the problem by identifying the source of polluted incoming air.

“The Infiltrometer test pinpoints where the bad air leaks are, and guides how to fix them,” says Reid. “Many can be easily repaired by homeowners as weekend projects. Others such as duct leaks are better left to the professionals. Finding and fixing the leaks that let in bad air will make your home healthier, less humid in the summer, less dusty, more comfortable, and even pay for itself through lower heating, cooling, and repair bills.”

The Comfort Institute recommends the Infiltrometer testing and consulting service to homeowners who:

  • Are considering a new air conditioner
  • Experience hot and cold spots in the home
  • Have excessive dust in their living space
  • Suffer from allergies
  • Tend to have high utility bills

“Controlling indoor humidity is just as important as controlling air temperature,” says Reid. “In the summer, a dry house is a comfortable, efficient, and healthy house. A sealed duct system, a reasonably tight house, and a properly sized, engineered, and installed air conditioner are the first steps. For homeowners wanting the healthiest and most comfortable home possible, a high-efficiency central dehumidifier is the next crucial element.”

© Comfort Institute Inc. 2002-2003 All Rights Reserved

What Does This Mean to You?

In addition to this helpful article provided by the Comfort Institute, we felt it necessary to provide a few additional tips that could be helpful to our local Boise market.

Have you ever been in a humid and moist climate? The thermometer may read 70 degrees, but it can feel like 85! Moist air is capable of holding a lot more heat. During the summer months, it is critical to reduce excess humidity in your home — not just for system efficiency but also for comfort. We recommend simply running the fan and circulating air throughout your home. This will help to reduce the build-up of humidity during the summer.

Since we live in a desert/arid climate, we often have to worry about adding moisture to our homes, especially during the winter months, when the relative humidity can often drop below 15% RH in most homes around the valley.

If you would like assistance with assessing and adjusting the humidity levels in your home, we can help! Contact us to schedule an in-home humidity analysis, FREE of charge, and receive additional guidance from our Boise area indoor air quality experts.


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