How to Install a Window Swamp Cooler (Evaporative Window Unit)

A window swamp cooler installs in an afternoon with basic hand tools, but the details decide whether it cools well and stays put. The unit must be supported by a bracket that carries its wet weight, sit level, seal tightly to the window, get a reliable water supply, drain its overflow outside, and have somewhere for the air it pushes in to escape. Below is the full process, plus the window-type quirks that trip people up.

If you have not bought the unit yet, read window evaporative coolers first. For whole-house rooftop or wall units, see the main swamp cooler installation guide.

Before you start: size, location and what you need

Window evaporative coolers typically move about 2,000 to 4,000 CFM. That is enough for one large room or a small home of a few hundred to roughly 1,200 sq ft, depending on ceiling height and climate. Check your space with the cooler size calculator.

Pick a window that:

• Faces the shadiest side of the house if possible. A cooler in full afternoon sun pulls hotter air and warms its own water.
• Is central to the rooms you want cooled, with a clear path for air to travel to an open window on the far side.
• Is within reach of a grounded outlet (no extension cord) and a hose bib or cold water line.
• Has solid framing and sill. Rotted sills or vinyl frames with no reinforcement need extra exterior support.

Tools

Tape measure, 2 ft level, drill/driver, 1/8 in and 3/16 in bits, adjustable wrench, utility knife, caulk gun, tubing cutter if using copper

Materials

Window bracket or support kit, exterior-grade screws or lag screws, filler panels (rigid foam, plywood or the kit panels), weatherstripping, exterior caulk, hose adapter or 1/4 in tubing kit, overflow tubing

Time

About 2 to 4 hours for one person and a helper for lifting

Measure the opening and choose a mounting method

Measure the inside width of the window opening at the sash track and the height of the open sash. Compare these to the cooler's discharge dimensions and the bracket's range. Most window coolers are designed for double-hung windows and need at least the full discharge height of clear opening plus room for the top filler panel.

Install the support bracket

An empty window cooler is manageable, but the water in the pan and soaked pads add a lot of weight, and wind loads add more. The sill alone should never carry it. Use the manufacturer's bracket or a heavy-duty universal window-unit bracket rated above the unit's operating weight.

1. Position the bracket. Set the bracket so the cooler's discharge will sit fully inside the opening and the cabinet clears the exterior siding, trim and any stucco ledges.
2. Fasten to framing. Drive the bracket fasteners into the sill framing or wall studs, not just siding or stucco. Pre-drill to avoid splitting.
3. Set the legs. If the bracket has adjustable legs that brace against the wall below, adjust them so the platform is level side to side.
4. Check pitch. Front to back, set the platform level or with the slight outward pitch the manual specifies (often no more than about 1/4 in). Never pitch it toward the room.

Set the cooler and seal the window

1. Lift and place. With a helper, set the cooler on the bracket and slide the discharge into the opening until the flange meets the frame or the stop.
2. Close the sash. Lower or slide the sash onto the top of the discharge or onto the kit's header strip so it holds the unit in place.
3. Fit filler panels. Cut panels to fill every gap beside and above the discharge. Rigid foam board or the kit's expandable panels work; seal edges with foam weatherstrip.
4. Secure the unit. Fasten the unit to the bracket with the supplied hardware, and add a sash lock or wood block so the window cannot be opened from outside.
5. Seal outside. Caulk exterior gaps that could let rain into the wall. Leave weep holes and the cooler's own drains clear.

Air leaking around the discharge is not just lost cooling: it lets cooler air loop back to the pads and lets hot air in. A good seal is worth the time.

Connect water and the overflow

Water supply is the biggest convenience factor. A 3,000 CFM window unit cooling air by 20 F evaporates about 3,000 x 20 / 8,186 = 7.3 gallons per hour, before bleed-off. A manual-fill pan holding a few gallons would run dry in well under an hour at that rate, which is why most window units in desert climates are plumbed with a float valve.

Hose connection

The simplest hookup is a hose bib adapter: a garden hose thread fitting that reduces to 1/4 in tubing feeding the cooler's float valve. Use a short, good-quality hose or tubing run, and add a shutoff at the hose bib. In full sun, a dark hose holds very warm water; that is harmless to cooling once it circulates but can grow algae if left sitting, so drain it when the cooler is off for long periods.

Permanent line

For a long-term installation, run 1/4 in copper or poly tubing from a cold water line with a tee and quarter-turn valve. Details and code notes are on the water supply and drain lines page.

Float, overflow and bleed-off

Set the float so the water stops about 1/2 to 1 in below the overflow. Connect a tube to the overflow fitting and run it to the ground, away from the foundation and not onto a walkway. If the unit has a bleed-off fitting, route it the same way or to plants that tolerate some mineral content. Bleed-off typically adds 25 to 100 percent to the water use; see bleed-off and water quality.

Power, controls and first start

Plug directly into a properly grounded 120 V outlet. If the outlet is outdoors, or anywhere water could reach it, it should be GFCI protected; modern code generally requires that. A window cooler's motor and pump draw well within a standard 15 amp circuit, but avoid sharing that circuit with a microwave, space heater or another large load. Do not use a light-duty extension cord; if you must extend, use a short, heavy-gauge, outdoor-rated cord matched to the unit's amperage.

1. Fill and check. Open the water, let the float shut off, and check for drips at fittings and pan seams.
2. Pre-wet. Run the pump alone for 2 to 3 minutes until the pads are evenly dark with water.
3. Open relief. Open a window on the far side of the room or house.
4. Start the fan. Start on low, then high. Listen for rattles at the filler panels and tighten as needed.

Relief air for a window unit

The cooler pushes outdoor air in, so it needs an exit. The rule of thumb is roughly 1 to 2 sq ft of open area per 1,000 CFM.

Open windows in the rooms you want cooled, so air is pulled through them. Closing them all turns the house into a pressurized, humid box. More detail in venting and relief air.

Seasonal removal and storage

In freezing climates, remove or winterize the unit each fall. Shut off and drain the water line, drain the pan, run the fan for an hour with the pump off to dry the pads, then either remove the unit or fit a cover and seal the window opening from inside to stop drafts. The full process is in how to winterize a swamp cooler.