Window Evaporative Coolers: Who They Suit, How to Size Them, What to Buy
Window swamp coolers explained: airflow ranges, room sizing math, window fit, water hookup, relief air, winter storage and how they compare to portable units.
Short answer
A window evaporative cooler is a compact fixed unit that sits outside a window and blows cooled air into one to three rooms, typically moving about 2,000 to 4,500 CFM. It suits renters, mobile homes and add-on zones in dry climates. Size it from room volume and climate, confirm the window fits, and plan a water line and relief air.
Key takeaways
- Window coolers move several times more air than most residential portables, enough for one large room or a small suite.
- Size by room volume: cubic feet x 20 to 40 air changes per hour / 60, using your climate's rate.
- At full output a window cooler can evaporate several gallons per hour, so a plumbed supply line beats manual filling.
- The cabinet must be supported from below or by a rated bracket, not by the window sash.
- Remove or seal the unit for winter to stop drafts and freeze damage.
On this page
A window evaporative cooler sits between a portable unit and a whole-house cooler. It is a fixed, outdoor-mounted cabinet with pads, a pump, a reservoir and a fan, designed to blow through a window opening into the room behind it. Because it pulls fresh outdoor air and moves several thousand CFM, it can cool a living room, a bedroom wing or a small apartment in a dry climate far better than any portable.
This guide covers who should buy one, how to size it, what has to be true about your window, and the features that separate a reliable unit from a frustrating one. For the step-by-step mounting process, see window cooler installation.
Who window coolers suit
Window units fill a specific gap:
- Renters who cannot cut a roof or wall but can get permission to use a window.
- Mobile and manufactured homes where roof structure or budget rules out a rooftop unit.
- Add-on zones such as a bedroom wing, converted garage or casita that the main cooler does not reach.
- Homes with central AC in dry climates where an owner wants cheap cooling for one heavily used room during the dry months.
They are a poor fit for humid climates (as with every direct cooler), for windows on upper floors without safe access, and for rooms with no possible exit path for relief air. Compare them with other categories in types of swamp coolers.
How window units compare with portables and whole-house coolers
| Factor | Residential portable | Window cooler | Whole-house cooler |
|---|---|---|---|
| Airflow | 200-1,500 CFM | About 2,000-4,500 CFM | 3,000-7,000+ CFM |
| Coverage | Spot or one room | 1-3 rooms | Whole house |
| Intake air | Indoor room air | Outdoor air | Outdoor air |
| Water supply | Manual tank, some hose | Supply line or hose with float | Plumbed supply with float |
| Installation | None | Bracket, seal, water, power | Roof or ground mount, duct, water, electrical |
| Equipment price | $100-$600 | $400-$1,200 | $600-$5,000+ |
One difference is easy to miss: a portable inside the room recirculates room air through its pads, so the room gets steadily more humid unless you ventilate well. A window unit always draws dry outdoor air, which is why it holds its cooling performance through the afternoon.
Sizing a window cooler
Use the same air-change method the site uses for every cooler:
Recommended air changes per hour depend on climate: about 40 in hot-dry desert areas such as Phoenix and Las Vegas (one change every 1.5 minutes), 30 in moderate dry climates such as Denver, Albuquerque and Boise (every 2 minutes), and 20 in mild or coastal-dry areas (every 3 minutes). The reasoning is explained in how to size a swamp cooler.
Worked example: living room and kitchen in Las Vegas
An open living room and kitchen of 520 sq ft with 8 ft ceilings holds 4,160 cubic feet. At 40 air changes per hour: 4,160 x 40 / 60 = 2,773 CFM. A window cooler rated around 3,000 to 3,500 CFM fits, leaving margin for the fact that pads and the window opening reduce delivered airflow below the free-air rating. In Albuquerque at 30 ACH the same space needs 2,080 CFM, and a smaller unit would do.
Run your own rooms through the cooler size calculator. If the result is well above 4,500 CFM, you are in whole-house territory or need two units feeding different rooms.
Fit: what your window must allow
Measure before you shop, because the window decides the shortlist.
- Opening width and height
- Each model lists a range of window widths and a minimum height for its discharge collar or adapter. Measure inside the frame, not the glass.
- Window type
- Double-hung and single-hung windows are simplest. Sliders work with a vertical filler panel. Casement and awning windows usually need a custom panel or a different opening.
- Support
- The cabinet sits outside and must rest on a rated bracket fastened to the wall framing or on a stand on the ground. A full reservoir and saturated pads add significant weight. Never hang it from the sash or sill alone.
- Height off the ground
- Ground-floor windows with a stand are easiest. Second-story installs need secure brackets and safe access for pad changes.
- Power
- Use a properly rated outdoor or nearby grounded outlet. Do not run an indoor extension cord through the window gap. Have an electrician add a circuit if needed.
- Water
- A nearby hose bib or a cold-water line for a 1/4 in or 3/8 in supply tube to the float valve.
Note: seal the gaps around the discharge with the supplied side panels or rigid foam and weatherstrip. Gaps let hot air and insects in and let cooled air short-circuit back outside.
Water: why plumbing beats a hose and bucket
A window cooler at full output evaporates a lot of water. The sensible cooling formula, 1.08 x CFM x temperature drop, and roughly 1,060 BTU absorbed per pound of water evaporated let you estimate it.
Worked example: hourly water use
A 3,000 CFM cooler dropping 100 F outdoor air by 25 F removes 1.08 x 3,000 x 25 = 81,000 BTU per hour, which takes 81,000 / 1,060 = 76.4 lb of water, or 76.4 / 8.34 = 9.2 gallons per hour at full rated airflow. Real delivered airflow is lower, so expect something like 5 to 8 gallons per hour on a hot, dry afternoon, plus any bleed-off.
Few reservoirs hold more than a couple of hours of that, so a continuous supply through a float valve is the practical choice. Add a bleed-off line if the unit supports one; it dumps a small steady flow to keep minerals from building up on the pads. See bleed-off and water quality and estimate your usage with the water usage calculator.
Features that matter
| Feature | What to look for |
|---|---|
| Pad media | Rigid cellulose for colder air and longer life; aspen for lowest price and easy replacement |
| Fan speeds | At least two; low speed is quieter at night |
| Pump control | Separate pump switch for fan-only ventilation and pad drying |
| Cabinet | Powder-coated or galvanized steel, or a polymer cabinet that cannot rust |
| Water hookup | Float valve with a standard fitting; drain plug for cleaning |
| Controls | Indoor control panel or remote so you are not reaching outside |
| Parts | Pads, pump and float sold separately and easy to find |
Look for replacement parts before you buy. Universal pumps and floats from parts suppliers fit many units, which matters more than a long feature list. For brand context, see evaporative cooler brands.
Common problems and how to avoid them
Most complaints about window coolers come from installation shortcuts rather than the units themselves:
| Problem | Usual cause | Prevention |
|---|---|---|
| Water running down the wall | Unit tilted toward the house, or overflow not piped away | Level the cabinet side to side with a slight tilt away from the window; pipe the overflow to the ground |
| Warm air from the grille | Dry stripes on the pads, low water, or air leaking around the pads | Check the distributor and float level; seat the pad frames properly |
| Room gets muggy | No relief opening | Open a window on the far side of the space |
| Rattling or humming | Loose bracket, panel contact with the frame | Add foam gaskets and tighten the bracket to the framing |
| Musty smell | Stagnant water, aging pads | Drain and clean the reservoir regularly, dry the pads with fan-only before shutdown |
Because a window cooler's reservoir is small, a slightly high float setting can overflow it within minutes. Set the water level a little below the overflow tube, following the manual's guidance.
Relief air, operation and winter
A window cooler pushes thousands of cubic feet of air per minute into a small space, so that air needs a way out. Open a window on the opposite side of the room or in the farthest room you want cooled, roughly 1 to 2 sq ft of opening per 1,000 CFM as a common field rule. Closing every other window and opening only the one where you want air to go "steers" the cool air through the house. The principle is covered in venting and relief air.
At season's end, shut off and drain the water line, drain the reservoir, dry the pads, and either remove the unit or cover it outside and seal the window opening inside with a rigid insulated panel. A cooler left in place with an open discharge leaks heat all winter and can be damaged when water in the line or pan freezes. The full routine is in how to winterize a swamp cooler.
Frequently asked questions
Can a window swamp cooler go in a sliding window?
Many can, with an adapter panel to fill the remaining height of the opening. Check the manufacturer's listed window size range and buy or build a weather-tight filler panel for the gap.
Do window evaporative coolers need a drain?
Most have an overflow and many have a bleed-off connection. Route both to the ground away from the foundation, a planter or a drain, so overflow water does not run down the wall or into the window frame.
Can I use a window swamp cooler in an apartment?
Often yes, but get the landlord's written approval first, since the unit needs bracket support, a water connection and sometimes an exterior outlet. Some HOAs and building rules restrict window units visible from the street.
How much electricity does a window evaporative cooler use?
Typically a few hundred watts depending on motor size and speed, far less than a window air conditioner of similar coverage. Check the nameplate for amps or watts.
Is a window swamp cooler better than a portable one?
For cooling a room, usually yes: higher airflow, a larger reservoir or plumbed supply, and outdoor air intake that stays dry. A portable is better only if you need to move it between rooms or cannot alter a window.
Sources and further reading
- Evaporative Coolers, U.S. Department of Energy, Energy Saver
- Champion Cooler and Essick Air owner's manuals, Champion Cooler / Essick Air
- Evaporative Coolers, Colorado State University Extension