Swamp cooler maintenance checklist
Updated August 2026
A swamp cooler runs on two appointments a year: a spring startup and a fall winterize, each a couple of hours of DIY. Startup means new or cleaned pads, a scrubbed reservoir, and a check of the float and pump; winterize means draining every line before the first freeze. Pads cost $20–60 and clog with mineral scale, so most owners in hard water swap them mid-season too. Done right, an evaporative cooler cools a dry-climate home for pennies against refrigerated AC.
| Task | Interval | Effort |
|---|---|---|
| Replace or deep-clean the cooler pads | Yearly | $20–60 · DIY |
| Scrub the reservoir and remove mineral scale | Yearly | 30 min · DIY |
| Set the float so water sits 1 inch below the overflow | Yearly | 10 min · DIY |
| Test the pump and oil the fan motor if needed | Yearly | 15 min · DIY |
| Reconnect water and check the belt tension | Yearly | 15 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Check pads for scale and even wetting | 2–4 weeks | 5 min · DIY |
| Add a bleed-off or drain-and-refill to cut mineral buildup | Weekly–monthly | 10 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Drain the reservoir and all supply lines before freeze | Before 32°F | 30 min · DIY |
| Disconnect and blow out the water line | Yearly | 15 min · DIY |
| Cover the unit or fit a rooftop cooler cover | Yearly | $20–50 cover |
What neglect costs
Skip the startup and old pads arrive at summer already stiff with scale, cooling poorly and smelling musty as they mold. A stuck float overflows the pan and can leak into a ceiling; a reservoir left full of standing water breeds algae. The costliest mistake is skipping the fall drain: water left in the lines freezes and splits the pump, the float valve, or the copper supply line, a $150–400 spring repair before you can even turn the cooler on. Fresh pads and a clean pan each spring keep a $1,000–2,500 unit hitting its full 15 to 20 year life.
Leave these to a pro
Most owners handle a swamp cooler start to finish, but two jobs are worth hiring out. A rooftop unit means ladder work over a roof edge, and paying a tech $100–200 for the seasonal startup or shutdown beats a fall. Second, if the fan motor whines, the bearings run dry, or the unit vibrates hard, a technician can replace the motor or pump before it seizes. In very hard water, some owners add a bleed-off kit or a small inline filter, a $30–80 upgrade a pro can plumb during startup. If you are comparing cooling options, see how it stacks up against a central AC or a mini-split.
This whole checklist ships as reminders in OnOtto: every task above, on the right schedule for your home, snooze-proof.
Load this checklist as remindersFrequently asked questions
When should I start up and shut down a swamp cooler?
Start it up in spring once nights stay reliably above freezing, typically April or May by region, so a late cold snap cannot crack a freshly filled line. Shut it down and drain it in fall before the first hard freeze, usually September or October. The two-appointment rhythm matters more than the exact dates: never leave water sitting in the lines through a freeze, and never run dry pads that have not been cleaned or replaced.
How often do swamp cooler pads need replacing?
Aspen (wood-fiber) pads usually last one season and get replaced every spring for $20–40. Rigid cellulose pads last 3 to 5 years but cost more, $40–60 or higher per set. In hard water, mineral scale clogs any pad faster, so check them every 2 to 4 weeks and swap mid-season if airflow or cooling drops. A quick tell: hold a pad up to the light, and if you cannot see through the crust, it is done.
Why does my swamp cooler smell musty?
A musty or fishy smell means mold, algae, or bacteria growing in a reservoir that stayed wet and dirty, or in pads that never dried out. Drain and scrub the pan, replace the pads, and run the pump on fresh water for a few minutes to flush the line. Adding a periodic bleed-off, where a little water continuously drains and refills, keeps minerals and slime from concentrating. Starting each season with a clean pan and new pads prevents almost all odor.
Is a swamp cooler cheaper to run than AC?
In a dry climate, yes, dramatically. An evaporative cooler uses roughly a quarter of the electricity of a refrigerated air conditioner because it runs only a fan and a small pump, no compressor. The trade-offs are that it adds humidity and only works well when outdoor air is dry, so it struggles in muggy weather and is a poor fit for humid regions. It also uses water, several gallons an hour, which factors into the running cost where water is scarce.