It’s not the heat, it’s the stupidity

Amy Musser

Who doesn’t love summer? Sweet tea, flip flops, and relaxing by the pool. Just try not to spend much time in attics, and be careful that those gym shoes in the bottom of your closet don’t get moldy. People ask me a lot of questions about air conditioning and humidity in the summertime, so I thought I’d dedicate this blog post to answering them.

When do I need a dehumidifier?
While there are a lot of things that will create some dehumidification in the summertime (your AC system, a heat pump water heater, certain ventilation systems), the only one that actually senses high indoor humidity and reacts in proportion to it is a dehumidifier. When you want to be really sure, it’s the best choice. Most of my clients are builders and designers who build homes and then other people live in them. You can’t plan for every scary thing someone might do. But a generally good strategy is to put a dehumidifier in any below-grade enclosed space (like a basement or conditioned crawlspace). Code allows you to rely on conditioned air from the home’s AC system to dehumidify these spaces, but in Asheville I’ve found that people often don’t run their AC enough. An off the shelf hardware store dehumidifier piped to a drain is an inexpensive insurance policy, and if the house is reasonably tight, it shouldn’t run a lot.

Can I get away with just a dehumidifier and no AC?

Probably not in WNC. It gets pretty hot here, and a dehumidifier generates some heat, which will make your house even hotter. Plus, unless you want to pay to dehumidify the outdoors, you’d need to close your windows, which will make it even hotter inside. At some point, you will want to stop fighting it and turn on the AC. Almost everyone who tries to go AC-free in this area eventually gives in.

To save energy, I’m only running my AC for a few hours in the afternoon and then I open my windows at night.
No one ever asks about this, they just tell me about this really smart energy saving idea they had. Well, I’m going to say what I think anyway: it’s using more energy than just leaving the windows closed and the AC on. Taking humidity out of air uses a lot of energy and takes a while. And, even though it’s cooler at night, it’s about as humid as it is during the day. If you open your windows at night and fill the house with super-humid air, then the AC will spend all afternoon pulling humidity out of the air, only to do it all over again the next day. The rule in my house is that if you’re not going to leave the AC on and windows closed for 3 days, don’t turn it on. I can be a mean person to live with.

What’s wrong with my AC? It runs all the time.

This is my personal favorite question! If you’re setting your thermostat at 75 degrees (or 78 if your spouse can stand it), and the AC is actually keeping the house at that temperature, then there’s nothing wrong with it. It sounds like you actually have a properly sized unit, which dehumidifies better than a unit that’s way bigger than you need. Bigger is not better in the world of AC – bigger means less efficient and more humid inside.

Final advice:
When you’re running your AC, don’t just close your windows – lock them. It makes your house significantly tighter. Remember to close the flue on the fireplace that you haven’t used in 6 months. Leave an AC vent open in every room to spread the dehumidification around the house better. For a happy dog, put the dog bed next to, but not on top of the AC vent. (Better yet, get one of those cool elevated beds and put it right over the vent.) Run the bath fan when you take a shower. Use a clothesline occasionally – it saves an unbelievable amount of energy. Use sunblock. Enjoy summer!

Copyright 2012 Amy Musser