How to Winterize a Portable or Window Evaporative Cooler for Storage
Store a portable or window swamp cooler so it starts clean in spring: drain the tank, dry the media, protect the pump and seal or remove the window unit.
Short answer
To winterize a portable or window evaporative cooler, empty and scrub the tank, run the fan alone for 1 to 2 hours to dry the media, clean or replace the pads, clear the pump and tubing, then store it indoors, upright and covered. Remove window units in cold climates or seal the opening with an insulated panel.
Key takeaways
- Drying is the main job. Run the fan with the pump off until the pads are bone dry, typically 1 to 2 hours for a portable and longer for thick rigid media.
- Empty the tank fully, including the last inch below the drain plug, and wipe out the scale and slime.
- Store portables indoors and upright, in a heated or at least above-freezing space, with the cord coiled and the tank cap off.
- Window units should come out of the window in cold climates. If you leave one in, seal it inside with an insulated panel and outside with a breathable cover.
- Write down pad size and model number at storage time so you can order replacements before spring.
On this page
Portable and window evaporative coolers do not face the same freeze risk as a roof unit, because they have no pressurized supply line on a roof. Their winter problems are different: damp media that grows mold in storage, a slime layer in the tank, a pump that seizes from dried scale, and, for window units, a cold, drafty gap in the window. Winterizing them is mostly a cleaning and drying job, done carefully once a year.
If you have a ducted roof or wall cooler, follow the main winterizing guide instead. This page covers plug-in portables (from small tabletop units to large commercial units such as Portacool and big Hessaire models) and window-mounted coolers.
What goes wrong if you skip it
| Problem found in spring | Cause | Prevented by |
|---|---|---|
| Musty or sour smell at startup | Damp media stored inside the cabinet; biofilm in the tank | Drying the media fully; scrubbing the tank |
| Pump hums but does not move water | Mineral scale dried on the impeller; seized shaft | Rinsing the pump in clean water and running it briefly before storage |
| Cracked tank, drain plug or pump housing | Water left inside during a freeze in a garage, shed or porch | Fully draining and storing above freezing when possible |
| Dry streaks on the pads | Clogged distribution holes or tubing from dried scale | Flushing the distribution line with clean water |
| Chewed cord or nest in the fan housing | Rodents in an unsealed storage area | Covering the unit and storing off the floor |
| Brittle, cracked casters or panels | Winter sun on a patio unit | Indoor or covered storage |
Step by step: winterizing a portable cooler
- Time
- About 45 minutes of work plus 1 to 3 hours of drying
- Supplies
- Soft brush, sponge, mild dish detergent, white vinegar, bucket, towels, a screwdriver for the back panel, a breathable cover or old bedsheet
- Turn off the pump but keep the fan running. Most portables have a separate "cool" or "pump" switch. Run the fan alone on high for 1 to 2 hours to dry the pads. Large commercial portables with thick rigid media may need 3 to 4 hours or a sunny afternoon outdoors.
- Unplug the unit. Do everything else with it disconnected.
- Drain the tank. Open the drain plug, usually on the bottom or lower back, and drain into a bucket or outdoors. Tilt the unit gently toward the drain to get the last of it. On units without a plug, remove the tank if it slides out, or use a wet/dry vacuum.
- Remove the media. Take off the back grille or pad frame. Note pad dimensions and model number for spring ordering.
- Scrub the tank. Use warm water and a few drops of mild detergent with a soft brush. For scale, soak with a mix of about 1 part white vinegar to 3 parts water for 30 to 60 minutes, then scrub and rinse. Rinse until no soap or vinegar smell remains.
- Clean the pump and water line. Pull the pump intake screen and rinse it. Set the pump in a bucket of clean water, plug in the unit and run the pump briefly to flush the tubing and distributor, then unplug, lift the pump out and let it drip dry. Scale on the impeller dissolves best in the vinegar soak; see scale removal and prevention for stubborn deposits.
- Clean or replace the media. Rinse cellulose rigid media gently with a garden hose on a low setting, never a pressure washer. Discard media that is crusted, crumbling or still smells after drying. Thin fiber pads in small units are usually cheaper to replace than to clean.
- Dry everything completely. Let the tank, pump, pads and housing air dry for several hours, ideally in sun or near a fan. Wipe the fan blades and grille while you wait.
- Reassemble loosely. Put the media back only once it is dry. Leave the drain plug out or loosened, taped to the unit so you do not lose it, so any residual moisture can escape.
- Cover and store. Coil the cord loosely, cover the unit with a breathable cover or sheet, and store it upright, off the floor, in a dry space.
Pro tip: Never store a portable on its side or back. Residual water runs into the motor and control area, and some units have tanks and float switches that crack when the weight shifts.
Where to store it
The best storage is indoors, dry and above freezing: a closet, basement or heated garage. An unheated garage or shed is acceptable for a fully dried unit, because dry plastic and motors tolerate cold. The risk comes from water left in the pump, the tubing and any ice-pack compartment. If you use a cold garage, drain twice: once when you do the cleaning and again the next day, after leftover water collects at the bottom.
Avoid outdoor storage, even covered. Winter UV, wind and freeze-thaw cycles shorten the life of plastic housings, casters and control panels. For large commercial portables that are too heavy to move indoors, use a heavy breathable cover, strap it down, and set the unit on blocks out of standing water.
Winterizing a window evaporative cooler
Window coolers are small evaporative units that sit in a window opening, blowing cooled air into a room. Many have a float valve and a 1/4 inch supply line like a roof unit, so they combine the water concerns of a roof cooler with the sealing challenge of a window. For background on these units, see window evaporative coolers.
Option 1: remove it (best in cold climates)
- Shut off water and drain. Close the supply valve, disconnect the line at the float valve, and drain it. Empty the pan via the drain fitting.
- Dry the unit. Run the fan alone for 1 to 2 hours with the window side still open, then unplug.
- Remove the unit with a helper. Window coolers commonly weigh 40 to 80 lb dry. Support it from outside and inside; never lift from the inside only.
- Clean, dry and store. Follow the same tank, pump and media steps as for portables. Store indoors.
- Restore the window. Reinstall the sash or storm window, or fit a temporary panel of rigid foam cut to the opening.
Option 2: leave it in place (mild climates)
In low desert areas where nights rarely drop much below freezing, many owners leave window units installed. If you do:
- Drain the water side exactly as you would for a roof cooler, including the supply line. See how to drain a swamp cooler.
- Seal the indoor side. Cut 1 inch rigid foam to fit the indoor opening and tape its edges, or buy a fitted interior cover. This is the warm side, so it is the seal that stops condensation and drafts.
- Fit a breathable exterior cover over the cabinet and strap it to the bracket.
- Check the window frame and support bracket for rot or rust while you are there. The window cooler installation guide explains what a sound mount looks like.
Warning: Do not tape plastic over a window unit from inside and leave it running "just the fan" in winter. Moist air behind plastic grows mold fast, and running an evaporative cooler in a cold, closed room raises humidity enough to cause condensation on windows and walls.
Cost and time: clean or replace?
Portable cooler media is a consumable. Deciding whether to clean or replace it comes down to its condition and price.
| Media type | Typical replacement cost | Clean if | Replace if |
|---|---|---|---|
| Thin fiber or honeycomb pad, small tabletop or room unit | $10 to $30 | Rarely worth it | Any odor, discoloration or stiffness |
| Aspen or synthetic fiber pad, medium portable | $15 to $50 | Light dust only | Scale crust, sagging, gaps or smell |
| Rigid cellulose media, 4 to 8 inch, large portable | $60 to $300+ per set | Light scale, no softening, no smell after drying | Crumbling edges, crushed flutes, heavy scale, persistent smell |
Worked example: storage decision for a large commercial portable
A shop owner has a large portable with two rigid media panels that cost about $150 each to replace (an illustrative figure). The media has light white scale on the inlet face but no softening. Cleaning takes about an hour and a few dollars of supplies. Replacing costs $300. Cleaning wins here, as long as the media is rinsed gently and dried for a full day before storage. If the same panels had crumbling edges, cleaning would just delay a $300 purchase by a season while costing cooling efficiency, so replacing would be the better call.
Spring startup for portables
When warm weather returns, unpack the unit, inspect the cord and plug, reinstall the media and drain plug, fill with fresh water, and run the pump for 10 minutes before turning on the fan so the media wets evenly. If it still smells after an hour of operation, the media needs replacing. Before a big purchase, check the portable cooler buying guide and use the cooling temperature calculator to confirm a portable will actually help in your climate.
Frequently asked questions
Can I store a portable evaporative cooler in the garage over winter?
Yes, if it is fully drained and dry. An unheated garage is fine for a dry unit, but any water left in the pump, tubing or tank can freeze and crack plastic parts, so dry it thoroughly first.
Should I remove the cooling pads before storing a portable cooler?
If the pads are removable, take them out, let them dry separately, and store them in a breathable bag or replace them in spring. Leaving damp pads inside the cabinet is the main cause of musty smells at startup.
How do I get rid of the smell in a portable cooler before storing it?
Scrub the tank with a mild detergent, rinse, and wipe with a solution of about 1 cup of white vinegar per gallon of water, then rinse again and dry fully. Replace the media if it still smells after drying.
Can I use a portable evaporative cooler as a humidifier in winter?
Some people run them with the fan on low in very dry indoor air, but they are not designed or rated as humidifiers. Keep the tank clean, avoid over-humidifying above about 50% RH, and check the manual before doing it.
Can I leave a window swamp cooler in all winter?
In mild desert climates, many people do, with an interior seal and an exterior cover. In areas with regular hard freezes or snow, removing it protects the unit and makes it much easier to seal the window properly.
Sources and further reading
- Evaporative Coolers, U.S. Department of Energy, Energy Saver
- Mold, U.S. Environmental Protection Agency
- Portable evaporative cooler owner's manuals, Hessaire, Portacool and Honeywell