Should I Cover My AC Unit for the Winter?

If you live somewhere that gets snowy winter weather, you might see quite a few people put covers over their AC units when they are done using them for the season. Maybe you do it, too. But should you?

Your HVAC system is expensive and anything you can do to prolong the life of your furnace and AC unit is something worth doing. Having recently spent a huge sum of money replacing everything in my HVAC system but the ducts themselves, I understand all too well the urge to keep your equipment in tip-top shape for as long as possible. Let’s take a look at when (and why) you would want to cover your AC unit and, more importantly, the right and wrong way to do it.

When Should You Cover Your AC Unit?

Although whole-house AC units are designed to be out in the elements 365 days a year—you can’t exactly unhook them and haul them into the garage after all—that doesn’t mean you have to let them bear the full brunt of bad weather.

Does that mean everyone needs to cover their AC units? Not necessarily. While it certainly can’t hurt to cover it up in the offseason, whether or not you want to go to the hassle of covering and uncovering it should be influenced by the following factors:

Proximity to Trees: If your AC unit gets hit with a lot of falling debris from nearby trees such as leaves, pine needles, or such, covering it up to keep the internal chamber from filling up with debris is worthwhile. Eventually, those leaves break down and create a moisture-retraining sludge at the bottom which will lead to rust and corrosion.

Precipitation: If your area gets a lot of precipitation in the offseason you may want to cover your unit to keep it dry. Doubly so if you get freezing weather and snow so that your AC unit isn’t subjected to ice and freeze/thaw cycles.

If you live somewhere hot enough in the summer to merit having an AC unit but not cold enough in the winter to have snow you can probably get away with not covering the unit.

If you live somewhere where the leaves drop in the fall, however, and there are trees close enough to your house to clog your gutters and dump leaves on the ventilation grill of your AC unit, you should still cover your AC unit in the offseason. It’s so much easier to prevent leaves from filling up the chamber than to unscrew a bunch of pieces to get inside to clean the leaves out.

When Should You Leave Your AC Unit Uncovered?

Rather than put this bit of information as a little note somewhere else in the article, we’re putting it in its own section for maximum visibility. There is one situation where you should never cover your AC unit.

If you have a heat-pump style HVAC system, commonly referred to as a “heat pump,” “packaged heat pump,” “all-season heat pump.” or a “combo HVAC unit” then it is critical you don’t put a cover on it.

Warning: Do not cover the external portion of a heat-pump AC system. Catastrophic damage to the HVAC system may occur.

Why do you want to avoid covering your heat pump AC? The way the unit is designed there is no “off-season.” The unit cools your home in the summer and warms it in the winter. You should leave all sides of the units uncovered all year long to ensure proper functioning.

While many people in the U.S. have a traditional furnace-AC arrangement where a stand-alone furnace provides the heat and then in the hotter months an external AC unit removes the heat, anyone with a combination unit needs to avoid covering the external part of the HVAC system.

When in doubt look at the model number on your unit and search in Google to determine what kind of AC unit it is and/or consult with a professional if you’re still unsure.

The Wrong Way to Cover Your AC Unit

If your situation calls for covering your AC unit, then it seems pretty simple right? Just go to local hardware store and grab a big boxy plastic bag cover or even wrap it up with a small tarp and some bungee cords. That’s what your neighbors likely do so it seems like the way you should too.

Except, not so fast. Covering up your AC this way is ultimately worse for your poor AC unit than not wrapping it up at all. Why? When you give your AC unit a Christmas-present-like wrap job that covers not only the top of the unit but also the sides all the way down to the ground you’re creating a chamber that traps moisture and accelerates rust.

Sure the total-coverage top-to-bottom covers will keep out rain and snow that fall directly upon the unit but as anybody who has stored anything outside with a tarp knows, eventually, moisture from the surrounding environment gets up and under a tarp. Even covers with little air vents and such on the side are imperfect at letting the moisture escape.

While the properly sized commercial covers are imperfect at best, doing what you see in the photo above—wrapping the entire unit in an oversized plastic tarp—is the worst method. There’s no breathability, no vents, just moisture rising up from the surrounding ground and getting trapped under the tarp.

The Right Way to Cover Your AC Unit

If wrapping your AC unit up tight with one of those big cube-like covers from the local hardware store is the wrong way to go about it, then what’s the right way? Perhaps counterintuitively, the right way to button your AC unit up for the winter isn’t bundling it up like a kid going to the playground but just covering the top like it’s wearing a hat for the chilly weather.

Use a Top-Only Cover

To that end, you just want a simple cover that prevents leaves, pine needles, and precipitation from shooting straight down the fan hole into the unit. Some people achieve that end by putting a piece of plywood sized to the footprint of the unit on top and then weighing it down with a brick. But that’s not a very elegant-looking solution and it puts unnecessary weight and pressure on the top of your AC unit.

Instead, we recommend using a heavy-duty and purpose-made mini tarp, like this model.

The tarp comes in 28″ x 28″, 32″ x 32″, or 36″ x 36″ sizes and features a square shape with grommeted corners. You simply lay it across the top of the AC unit, with a diamond slant (so the corners of the cover fall in the center of the AC unit sides and not at the corners) and then secure it with the little bungee cords that come with the kit.

Note: Don’t pull the bungee cords super tight. You just need a slight amount of tension to hold the cover in place. Maxing out the tension doesn’t make it work better and it might deform the AC grill.

To give you a sense of scale, the photo above shows a 36″ cover on my Lennox XC20 air conditioner which is, as far as residential whole-house air conditioners go, a shockingly large unit. The XC20 is slightly oblong with a 36″ width and a 39″ length. With the 36″ cover strapped down with a slant, however, it’s still more than adequate to cover the opening and keep leaves and snow out. When in doubt just buy the 36″ model. A few extra inches down the side of the unit makes no difference but returning a too-small size is a hassle.

Shortly after I put the cover on for the season, we had a huge rain and windstorm that demonstrated how good a job the cover did at keeping debris out. The water just beaded up on top and the leaves that landed on the cover simply blew away once the sun came out and dried the water up.

Modify Your Old Cover

If you already have one of the big cube covers you paid good money for and you don’t want to just toss it, don’t worry. You can easily modify it to still cover your AC unit while letting air flow freely through the sides so moisture doesn’t build up.

All you need to do is purchase a cheap grommet kit, often called a “tarp repair kit”,  and some short no-scratch bungee cords. If you already have both laying around in your garage you’re halfway done.

Just cut the excess length off your cover so it’s more of a cap with an 8-12″ drop on each side instead of a full cube-shaped cover. Add a few grommets along the sides and then use the bungee cords to keep it from blowing away. If you want to clean up the cut edge so it doesn’t fray, just carefully and lightly wave a lighter flame along the edge to melt the fibers (all the covers are some type of plastic, be it woven nylon or otherwise so a little heat will seal the edge).

Set a Reminder to Remove the Cover

Your AC unit won’t function very well with the cover in place and can even be damaged by it, so you’ll want to be sure to remove it before AC season is upon us again.

It doesn’t matter what date you use as your reminder as long as that date is in your calendar and falls before the time of year where you turn the AC on.

For most people adding it to your list of Daylight Saving Time tasks is an easy way to remember or tacking it onto your list of spring tasks like getting the garden hoses out and such.

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It might seem like a hassle to cover your AC unit, but with the price of everything perpetually going up, a few minutes twice a year spent messing with the cover can save you quite a bit of money over the years.