Along the Gulf Coast we have come to live with the heat and air conditioning 8 or 9 months out of the year. However, worse than the heat is the humidity. In a typical year we may see 70 – 90 days of temperatures above 90 degrees. Couple that with humidity readings in the 80 and 90 percent range almost year round and you have air you can wear. Taking a shower in the morning is futile because you feel gross simply by walking out to the car later in the morning. Humidity is a beast that must be dealt with.
In modern homes that are very tight, where air cannot migrate inward and outward freely, humidity is the number one concern. Moisture can kill a house built to today’s building and energy conservation codes. Sure, for decades we have come to appreciate our air conditioners for their ability to pull that humidity out of our air so we could live comfortably indoors. We used to joke about having an A/C unit that could run almost 24 hours a day. We may have joked but that long run time by that miracle of technology kept humidity levels low indoors.
Let's fast forward to homes built today. For this, allow me use my new house as an example of what can happen in a modern house. We recently moved in to our reconstructed house. If you’ve kept up with my blog you know I’ve done some cool stuff and really built it right for our climate. I utilized spray foam insulation so my house now acts like a giant YETI cooler that does not leak air. My wife loves to keep the thermostat set at about 73 degrees.
On a recent Saturday our power went out around lunch time. We were without air conditioning for almost 11 hours before the power was restored on a day where temps soared well over 90 degrees. (If you have a good deal on a backup generator please let me know) When the digital thermostat came back to life just before midnight the big ol’ numbers on the screen read “74”. Wow! In 11 hours, during the heat of the day, the temperature in our house only went up one degree. That insulation stuff really does work. However, something else had happened.
You see, for 11 hours we lived inside that YETI cooler. We showered, cooked, cleaned, opened and closed doors, and other normal Saturday kind of stuff. Although the temperature didn't vary much indoors something else happened during all that activity. The indoor relative humidity crept up to 84%. EWE! That’s sticky! It normally stays just below 50%.
In today’s modern homes air conditioners do not run as much due to really good insulation and the fact that hot humid air doesn’t migrate into them. Without that big ol’ machine running humidity will increase in any home much less one on the Gulf Coast. So what do we do? Turn the thermostat down to 68 so the machine will run? No! If you can keep the indoor humidity around 50% or below you will find that higher indoor temperatures are quite comfortable. However, let the humidity rise to let’s say 84% and the same indoor temp now feels sticky and gross.
Under normal circumstances my A/C doesn’t run much during the day even when it’s 90-something degrees out there. So how do I control humidity? For any fairly tight home I recommend the use of a whole house dehumidifier. You can buy a portable unit and try it out in your house. For an average house a unit that will remove 70 – 90 pints of water per day would be great. If you want to upgrade do what I did and have a unit built into your A/C system.
I have a 98-pint unit made by Ultra-Aire. It is wired into, and is controlled by, my thermostat. This quiet machine now lives in the attic right next to the A/C unit. If the A/C is not running it can keep the indoor air nice and dry. During what we call the “Swing Seasons” (when you don’t run the A/C) a dehumidifier will keep the humidity down inside the house when the A/C is not running.
Low indoor humidity has a lot of benefits to consider besides just your comfort level. It keeps condensation from happening in many situations. Some folks with breathing issues may find taking a breath easier when humidity levels are lower. Some common indoor air pollutants like dust mites, bacteria, and viruses can be reduced. Finally, molds tend to grow and party when moisture levels get high. Keep moisture levels low - mold isn't a problem! Depending what articles you read, indoor relative humidity levels between 40 and 60 percent are optimal. (Being too dry has its own problems but we can discuss that some other time.)
The humidity level on my thermostat is set at 55%. On any given day so far this summer my indoor humidity levels hover between 47 and 54%. Not bad considering my air conditioner is barely running.
If you are building a new home, or maybe rebuilding a flood damaged home right here in my neighborhood, talk to your A/C contractor about a whole house dehumidifier. It’s a true work horse that will keep you healthy while keeping you comfortable.