The short answer

  • Pull the unit out of the window if you can. Drain it, clean it, dry it, and store it upright.
  • Run it on fan-only for about an hour before removal so the inside coil dries out.
  • Store it standing up, off a concrete floor, under a breathable cover. Never sealed in plastic.
  • A cold garage or shed is fine. A damp one is not. Moisture, not cold, is what ruins a stored unit.
  • If the unit has to stay in the window, seal the indoor side and cover the outdoor side with something that breathes.

Take the unit out of the window, drain the water sitting in its base pan, wash the filter, let everything dry for a day or two, then store it upright in a dry place. That is the whole job, and it takes about an hour of real work. Updated September 11, 2026.

The part people skip is the drying. A window air conditioner holds water on purpose, and sealing a damp unit in a plastic bag for six months is how you end up with a musty smell in May.

What this covers

When should you take a window air conditioner out for the winter?

Pull it once overnight lows settle into the 50s and you have stopped reaching for the remote. In most of the US that lands somewhere between late September and mid October.

There is no reason to wait for the first freeze. Waiting just means you are wrestling a heavy metal box on a cold, wet day, and a unit full of standing water can freeze and crack the drain pan.

Pick a dry afternoon. You want the unit to air out indoors afterward, and that goes faster when the house is not already damp.

How do you store a window air conditioner step by step?

Here is the order that matters, because doing them out of sequence creates extra work.

  1. Run the unit on fan-only, no cooling, for 30 to 60 minutes. This dries the evaporator coil while it is still in the window.
  2. Unplug it. Do everything else with the cord out of the outlet.
  3. Drain the base pan. Most units hold water by design and sling it onto the condenser coil. Tilt the unit slightly toward the outdoors and let it empty through the drain hole before you touch the brackets.
  4. Remove and wash the filter in warm soapy water. Set it somewhere airy to dry completely.
  5. Vacuum the coils and fins with a brush attachment. Wipe the housing. If the fins are bent, a cheap fin comb straightens them in a few minutes.
  6. Take it out. Remove the sash screws and accordion side panels first, then lift with a second person, one inside and one supporting the outside.
  7. Tilt the unit over a tub or sink to release any water that was still trapped, then let it sit indoors for 24 to 48 hours before you cover it.
  8. Cover it loosely and store it upright.

Most 5,000 to 12,000 BTU units weigh roughly 40 to 80 pounds, and they are awkward more than heavy. Do not do the removal alone from a second-floor window.

Should you store a window AC unit upright or on its side?

Upright, in the same orientation it sat in the window. Compressor oil pools where gravity puts it, and laying a sealed refrigerant system on its side or upside down lets that oil migrate into places it should not be.

If a unit does get stored flat or tipped, stand it upright for at least 24 hours before you plug it in next spring. That gives the oil time to drain back.

Upright storage also keeps any leftover water in the pan instead of running into the electrical compartment.

Where is the best place to store a window air conditioner?

A dry spot with steady airflow, raised off a concrete floor. A garage shelf, a closet, a basement with a working dehumidifier, or a spare bedroom corner all work.

Cold does not hurt the unit. Refrigerant and a compressor handle freezing temperatures without complaint. What hurts it is condensation, which is why an unheated but dry garage beats a warm, humid basement.

Concrete wicks moisture and stays colder than the air above it, so set the unit on a pallet, a scrap of plywood, or a shelf. Two inches of separation is enough.

Do window AC units need to be covered in winter?

A stored unit needs a light, breathable cover to keep dust off, and nothing more. A moving blanket, an old sheet, or the original box does the job.

Do not wrap it in a trash bag or shrink-wrap it. Sealed plastic traps whatever moisture is left inside and turns the cabinet into a small terrarium for mold.

A unit that stays in the window is a different case. Cover the outdoor half to keep snow, ice, and leaf litter out of the fins, and use a cover with vents or a canvas-style fabric rather than an airtight vinyl sack.

What if you cannot take the unit out of the window?

Then seal the indoor side, because that is where your money leaks out. A window unit sleeve has gaps around the chassis, through the vent damper, and behind the accordion panels, and together they can leak like a window cracked open all winter.

An insulated indoor cover that straps over the front and seals at the edges is the single most effective piece. Add foam weatherstrip in the gaps around the sleeve and adhesive-backed foam along the accordion panels.

Outside, cover the top and back so meltwater cannot sit on the coil and refreeze. Leave the bottom open so any moisture that gets in can drip out. Sealing an outdoor cover at the bottom is how people end up with a block of ice sitting in the drain pan, and it is the same trapped-moisture problem that shows up in other household fixes where airflow matters more than the product itself.

How do you keep mice out of a stored window air conditioner?

A window AC is a warm, sheltered box with soft insulation inside, which makes it prime real estate once temperatures drop. Store it indoors if you can, and stuff steel wool or copper mesh into the large coil openings if it lives in a garage or shed.

Mice chew wiring and nest in the blower housing, and you will not know until the unit rattles or smells in June. A unit left in the window is even more exposed, since the outdoor grille is an open invitation.

Skip mothballs and dryer sheets. They do not keep rodents out, and the smell ends up circulating through your bedroom next summer.

What can you skip?

You do not need coil cleaner spray, a fitted branded cover, or a storage bag sold specifically for air conditioners. A vacuum, dish soap, and a spare blanket cover the whole job.

You also do not need to have the unit professionally serviced before storage. Window units are sealed systems with no user-serviceable refrigerant, and a fall tune-up on a $200 appliance is money better kept.

The one thing worth buying, if the unit stays in the window, is an insulated indoor cover. That is the piece that pays for itself in heating, and you can usually find one in the home and seasonal deals we track this time of year.

Frequently asked questions

Can I leave my window AC in the window all winter?

You can, and plenty of renters have no choice. Expect cold air infiltration around the sleeve, so seal the indoor side with an insulated cover and weatherstrip. Cover the outdoor half with breathable fabric to keep ice and debris out of the fins.

Do I need to drain a window air conditioner before storing it?

Yes. Most units intentionally hold water in the base pan to sling across the condenser coil, so there is usually standing water even after a dry week. Tilt the unit toward its drain hole, let it empty, then let the whole thing air out for a day or two before covering it.

Can a window air conditioner be stored in an unheated garage?

Yes, as long as the garage is dry. Freezing temperatures do not damage the sealed refrigerant system or the compressor. Raise the unit off the concrete floor and keep it under a breathable cover instead of plastic.

Should I cover a window AC unit with a plastic tarp?

No. Plastic traps condensation against the metal and encourages rust and mold inside the cabinet. Use canvas, a moving blanket, or a vented cover that lets air move through.

The whole thing comes down to one rule: get the water out, then keep water away from it. Everything else, the covers, the sprays, the storage bags, is optional at best.

September is the month a lot of household gear changes places, and the same forced-air heat that starts running this month dries out skin and hair along with the house. If that is already showing up, our notes on starting retinol without irritation and protecting color-treated hair from heat cover the indoor-air side of the season. And if a winter trip is on the calendar, the rundown on dual voltage flat irons saves a fried appliance abroad.