How to Winterize a Swamp Cooler (Fall Shutdown Step by Step)

Winterizing a swamp cooler means three things: get every drop of water out of the supply line and pan so nothing freezes, leave the cabinet clean and dry so it does not corrode over winter, and seal the opening into the house so heated air stays inside. Most homeowners can do it in 1 to 3 hours, and the best time is right after your last hot spell, before the first night below freezing.

The steps below fit typical roof-mounted downdraft and side-draft coolers. Follow your manufacturer's manual where it gives specific instructions, especially on belts and pads.

When to winterize

Use the first forecast hard freeze as your deadline. Your local National Weather Service office publishes freeze outlooks, and NOAA climate normals show average first-freeze dates. As rough guides: high-elevation towns such as Flagstaff, Santa Fe or the Colorado Front Range often see first freezes in late September or October; mid-elevation cities like Albuquerque, Salt Lake City, Reno and Boise usually sometime in October; low desert cities like Phoenix and Las Vegas may see only occasional light freezes, mostly from late November through January, and some winters none at all. Check our climate index for your region's cooling season.

Wait until you are sure you are done with cooling. Many owners in hot climates keep the cooler running into October; that is fine as long as you shut the water off before a freeze.

Tools, time and safety

Time

1 to 3 hours depending on how dirty the pan is and whether you need to work in the attic

Difficulty

Easy to moderate; roof access is the main challenge

Tools

Nut driver or socket set, adjustable wrench, wet/dry shop vac or sponges and bucket, plastic scraper, stiff brush, flashlight, bucket for draining the line

Supplies

Cooler cover sized for your cabinet, bungee cords or tie-down straps, a ceiling vent seal or magnetic register cover if your cooler blows through a central ceiling diffuser

Step-by-step winterizing

1. Turn off the power. Thermostat off, then the disconnect or breaker. Confirm the blower and pump will not run.
2. Shut off the water. Close the cooler's supply valve. It is commonly a small saddle or angle valve on a cold water line in the attic, a utility room, near the water heater, or at an outside hose bib. Label it now if it is not already labeled.
3. Drain the supply line. On the roof, disconnect the supply tube from the float valve with a wrench and let the line drain. Many installs have a drain cock or tee near the shutoff; open it and catch the water in a bucket. Blowing out the line with low-pressure air helps on long runs in cold climates.
4. Drain the pan. Unscrew the overflow standpipe or open the drain fitting. Let all water out, including from under the pump.
5. Unplug and clean the pump. Unplug it from the cooler's receptacle, lift it out, rinse the screen, let it dry, and either store it indoors or leave it upright in its bracket. Storing it dry keeps minerals from cementing the impeller.
6. Clean the pan and frames. Vacuum out sediment and scrub scale. Dry the pan with towels. Touch up bare metal with a coating your manufacturer approves. See how to clean a swamp cooler.
7. Deal with the pads. Aspen pads are usually removed and discarded, or left in to dry and replaced in spring. Rigid media can stay if dry. Do not seal up a cooler with wet pads.
8. Belt and bearings. Some manufacturers suggest slackening or removing the belt so it does not take a set over winter; others say to leave it. Follow your manual. Note the belt size in your log so you can buy a spare.
9. Leave the drain open or the standpipe out so any rain or snowmelt that gets past the cover drains away instead of pooling.
10. Reinstall the panels and cover the unit. Fit a cooler cover and secure it with bungees or straps under the cabinet. Make sure it cannot lift in wind.
11. Seal the duct from inside. Close the duct damper if you have one, and seal the ceiling diffuser with a vent cover or insulated plug. This step does the most for your heating bill.

Why sealing the duct matters so much

A swamp cooler is essentially a large hole in your roof with a fan in it. Even with a cover, an unsealed duct lets warm, moist house air rise into the cooler, where it loses heat and can condense on cold metal. The result is heat loss, dripping, and rust inside the duct.

Cover choices

Measure height, width and depth of the cabinet before buying a cover; sizes are typically listed by cooler CFM or cabinet dimensions.

Whatever cover you use, check it after the first big wind and after heavy snow. A cover that has shifted can funnel water into the cabinet instead of shedding it. Covers typically last 3 to 6 seasons before UV makes them brittle; replace one that has cracked seams or holes rather than patching it with tape, which peels in cold weather. Store the cover folded and dry over summer so it does not mildew.

Regional differences

Cold, high-elevation climates

Blow out the supply line with air, consider removing the float valve and storing it indoors, and use an insulated cover plus an inside seal. Snow loads can crush cheap covers, so check after big storms.

Low desert climates

Freezes are rare but do happen. Shut off the water and drain the line anyway, because a single hard freeze can split a plastic float valve. Dust storms are the bigger issue; a cover keeps sand out of the pan and bearings.

Homes with dual systems

If you switch to a furnace or heat pump in winter, also check that the cooler and furnace ducts are properly isolated. Many systems use a manual damper or a barometric damper; confirm it is closed. See ductwork for evaporative coolers.

Common winterizing mistakes

• Draining the pan but not the line. The line between the shutoff and the float still holds water and is the most common winter break. See water supply and drain lines.
• Leaving the pump in standing water. Minerals set up hard, and the pump will not start in spring.
• Covering a wet cooler. Trapped moisture feeds rust and mildew; the first spring run smells musty. See swamp cooler smells.
• Forgetting the inside seal. The cover alone does not stop warm air from rising into the duct.
• Leaving power on. A thermostat bumped to cool in winter can run the blower with no water and pull in freezing air.

What pros check during a shutdown

Technicians commonly use the shutdown visit to spot parts that should be replaced before spring: a pump that sounded weak, a belt with cracks, bearings with play, rust at pan seams, a float valve with scale, or a roof jack with failing sealant. Writing those down now lets you buy parts in the off-season. In spring, follow the spring startup checklist and the rest of the maintenance schedule.