We’ve all heard this infamous phrase, and as much as we hate it, it is very true- especially here in the humid South. Here in Central Kentucky, we are not truly an air-conditioning climate, but we are considered a “de-humidification” climate. This means our air-conditioner’s #1 job is to dehumidify our homes all while cooling them at the same time. Humidity is very important to our perception of comfort, as every 5% change in humidity impacts our perception of temperature by 2-3 degrees. For example, 80 degrees in Phoenix, Arizona is very comfortable because their average humidity is only 33%. Lexington’s humidity averages twice that amount at 67%, which means an 80-degree day here feels 6-7 degrees hotter than it does in Phoenix.
These differences are even more important inside our homes, where we can create a controlled environment with perfect temperature and humidity. We’ve talked in previous articles (link here) about how important it is to tighten and insulate our homes to allow better control from our HVAC equipment, and once we have that tighter structure, we can use properly sized HVAC equipment to not only keep perfect temperature, but also perfect humidity. Older style, or even newer base model air-conditioners, do a poor job of dehumidifying because they are a one-size-fits-all system focused on cooling. As previously mentioned, Kentucky is not truly a cooling climate, so these systems do not do a very good job of properly dehumidifying and they can even cause comfort issues. That’s right; many times, when we are called in to help a homeowner with comfort issues, the air-conditioner is actually the cause of the problem. The sad part is most heating and cooling contractors do not understand the physics of comfort and indoor air quality and their typical approach to correcting comfort issues is to offer a bigger system- which is the exact opposite of what is needed.
When it comes to an air-conditioner, bigger is almost never better. In my almost 30 years in this industry, I can just about count the number of times that I increased the size of an air-conditioner. In contrast, we actually reduce the size of systems on a weekly basis. A bigger air-conditioner will satisfy your thermostat faster and run for shorter periods, but because the thermostat typically only reads temperature not humidity, it’s only addressing half of the issue. Shorter run times for air-conditioning are not a good thing; instead, we want longer run cycles that take more humidity out of the air. An air-conditioner running less than 7.5 minutes per cycle removes 0% humidity and on a leaky house this will likely add humidity to the home. This damp, muggy air is not comfortable and can lead to mold and other allergy issues. On top of that, oversized systems running in short cycles use dramatically more energy and have a shorter life expectancy than systems with longer run cycles- think of it like city versus highway driving in your car. Highway driving gets much better gas mileage, and the miles add up to less wear and tear on the car, causing it to last much longer- the same goes for your air-conditioner!
Technology is helping the HVAC industry to do better. Today, we have 2 stage air-conditioners with a lower, smaller gear that encourages longer run times. This is not new technology, as it has actually been available since the early 80’s, but it still makes up a very small percentage of systems sold today. The latest and most advanced air-conditioners are what are called variable volume systems. These systems work much like a dimmer switch on a dining room light. They start on a very low gear and only speed up when needed. This allows for very long run cycles and offers 5 times the dehumidification of a single stage system. Most of these systems have settings on their thermostats that allow for advanced dehumidification, so you can set them to control not only temperature but humidity as well. As a bonus, because these units run at slower lower speeds, both the outdoor unit and indoor fan are among the quietest air-conditioners on the market.
If you are not in the market for a new air-conditioner, a whole house dehumidifier from brands like Honeywell and Aprilaire can help you keep summer humidity in check. Skip the portable units from the big box stores, as they typically do not remove enough humidity to make an impact on the whole house and tend to be energy hogs- using 3-5 times the energy of Honeywell whole house model.
Ideal summer humidity range is 45%-55%, so if you can keep it under 50% that’s pretty much perfection in the South! It’s almost impossible to get humidity levels too low in the summer, so we recommend setting your dehumidification set point as low as it will go.
Humidity control is not just about comfort, it’s about air quality as well. Many allergy issues are aggravated by high humidity levels. I mentioned earlier that mold and mildew are created by high humidity, but did you know that dust mites also thrive in these conditions? They don’t drink, but instead they absorb moisture through their skin. In fact, if you keep the humidity below 50% in your home there’s not enough moisture in the air for dust mites to live! So, controlled humidity not only makes you more comfortable, but it improves your air quality and overall quality of life in your home.