It’s cool in most of the country now and that means it’s time to go through the last few steps needed to get your home ready for winter. For those of you who have window AC units you should almost definitely take them out and store them properly inside. However, the question of whether you need to cover a central AC unit still remains a murky one, with a lot of “heated” debate on both sides.

Here’s my air conditioner cover after a heavy snow and ice storm.

It protected my AC exactly as it was designed to do.

First, the basic facts about central air conditioners. The most common central air conditioner system is a “split” system which has two parts: the evaporator coils and air unit inside the house and that metal box with a large fan, a condenser coil and a compressor on the outside of the house. Most people refer to that large metal box with the vent slits in the side as the “air conditioner” even though it’s just one part of the total system. We’ll call it that, too.

These air conditioners are built to be sturdy and to stand up to all kinds of weather year after year. A typical central air conditioner should last you ten years or more with some basic air conditioner maintenance from time to time. Most air conditioner manuals do not mention covering the AC unit during colder months but that isn’t always the best measure of what to do with a piece of hardware.

That being said, there are a lot of things that can go wrong with an air conditioner units when it’s left in the elements. The coils in the air conditioner are designed for a certain efficiency level and as they get dirty or bent or covered up your AC will begin to lose its efficiency and may not cool your home as well or at least as cheaply as it once did. The longer and harder your AC has to work to cool your home, the more electricity you use, the more expensive it is to run it. So it’s pretty important to keep your outside air conditioner coils free of as much dust, dirt, leaves, bugs, small animals and other outside yard debris as you can.

That’s where the idea for an AC cover comes in: it covers your air conditioner for a good 5 to 6 months out of the year and prevents just about anything from getting into your AC unit and disturbing the coils. During the winter months that means that the wind won’t blow in leaves or grass or twigs or anything else. It also means that will most likely avoid getting large blocks of snow and ice in your air conditioner, which could severly damage the coils. Remember: water expands when it freezes, so a little water or snow on the coils during the day could quickly turn to ice that night and bend and buckle your coils.

So why wouldn’t you cover your air conditioner during the winter months? Some experts argue that some AC covers actually trap moisture inside your air conditioner for long periods of time which could then lead to the rust as well as the exact same icing problem as when it wasn’t covered. Others point out that covers on AC units keep them dry and relatively clean and free from a steady cold wind - which makes them a perfect place for mice, chipmunks and other critters to snuggle in for the winter and chew your air conditioner’s wires to shreds.

To summarize, here are the pros and cons of covering your AC unit in the winter months:

Pros to covering your air conditioner:

• Keeps your air conditioner coils a little cleaner so it may run a little more efficiently when you use it again
• Prevents heavy debris like sticks, branches and other yard waste from blowing into your AC
• Helps prevent water from directly resting on your coils and freezing, which could be damaging
• May save on maintenance costs and help lengthen the life of your air conditioner

Cons to covering your air conditioner:

• Could trap in moisture if not done properly
• Could provide a tempting spot for small animals to nest during winter months
• Most AC manufacturers don’t specifically recommend covering the outside unit

A lot of these issues can also be affected by different factors. For example, where you live largely determines the kind of weather you have during the winter. People in living in Florida obviously have less snow than people living in Maine. The type of AC cover you are using will also determine a lot about how much moisture could be trapped inside your air conditioner. So here are a few options:

Cover Your Air Conditioner with Nothing: Yep, you can do this. Again, most manufacturers don’t mention covering their AC units at all. But then again, most car makers don’t specifically warn against driving into trees. Air conditioner units are expensive to replace and even repair should something happen to it. If you’re not going to use air conditioner for a good six months or so out of the year it makes logical sense to close it off from the elements, at least a little bit. Covering your ac unit each year may allow it to last and run a little longer.

Cover Just the Top of your Air Conditioner: A lot of people choose taking the middle ground with an AC cover. They cover the top of their unit with a piece of plywood and secure it using a heavy brick or rock. This prevents most of the snow and ice from entering your AC unit from the top and it still leaves the sides open for plenty of cool air to blow through, eliminating the trapped moisture problem.

Fully Cover Your Air Conditioner: If you fully cover your air conditioner, you’ll want to take a few things into consideration. Using plastic makeshift AC covers out of things like tarps or large plastic bags are not a good idea because they can easily keep moisure stuck inside for a long time. They will also almost certain rip or blow off during a long winter unless you get pretty creative with your fastening. If you’re going to go with a full cover then you might want to consider using a specially designed air conditioner cover like the one I picked up. I like the full cover because it lessens the chance of debris and water from entering the sides of my air conditioner. I haven’t had any trouble with animals or humidity, but I do go out every two or three months and just check it out, making sure it’s still secure and nothing unwanted has made it’s way inside.

The professional air conditioner cover I use is a thick vinyl and felt lined so it slides on easily and it absorbs some humidity. It also a Velcro strip that can be adjusted at one corner and it has elastic straps in the corners to keep the cover secure in rough weather. It fits my AC unit like a glove. As you can see in the photo, it protected my air conditioner from an unexpected snowstorm and subsequent ice meltings and refreezings.

I opted to cover my new air conditioner last year and I haven’t had any problems yet. I have a lot of trees on my property which means I have a lot of leaf clean up during the fall and tree debris blowing around my home. Our winters are mostly dry where I live but when we do have moisture it’s usually in the form of snow or sleet. For me, an air conditioner cover made sense and so far it’s been working well!