Swamp Cooler Installation Guide: How to Install a Roof, Wall or Window Evaporative Cooler

A swamp cooler installation has five parts: a level, well-supported mount; a duct or discharge path into the house; a cold water supply to the float valve; a drain and bleed-off line; and a safe electrical circuit with a control. Get those right, add enough relief air, and the cooler will run for a decade or more. Get one wrong and you will be chasing leaks, weak airflow or a tripped breaker all summer.

This guide walks through the whole job in the order a technician plans it, with the numbers that matter at each step. The detailed sub-topics have their own pages: ductwork, relief air, water and drain lines, controls and window units.

Choose the installation type

Where the cooler sits decides most of the work. There are three common layouts for homes, plus portables that need no installation at all.

Downdraft units deliver air straight down through the ceiling and are the most common whole-house choice in the Southwest. Side-draft units avoid roof penetrations and are easier to service from the ground. If you are still deciding, see downdraft vs side-draft coolers.

Confirm size and climate before you buy

A cooler that is too small runs flat out and still loses. A cooler that is far too large drafts and over-humidifies small homes. The working rule is one full house air change every 2 to 3 minutes, which is 20 to 30 air changes per hour (ACH).

Run your own numbers with the cooler size calculator, and check how much cooling your town's design weather allows in the climate index. Sizing details are covered in how to size a swamp cooler.

Pick the location and plan the structure

Rooftop units

Place a downdraft cooler as close to the center of the house as the roof framing allows, so one ceiling diffuser can reach the main living areas. Keep it away from plumbing vents, furnace flues and dryer exhaust, which the cooler would otherwise pull into the pads. A common clearance target is several feet from any vent or flue; follow the manual and local code.

Weight is the issue people underestimate. An empty residential downdraft cooler is light enough for two people to carry up a ladder, but add wet pads and a full water pan and the operating load climbs to several hundred pounds concentrated on a small footprint. The roof stand must bear on rafters or truss top chords, ideally spanning at least two framing members per leg, with sleepers or a flashed curb so the legs do not punch through the roofing.

Ground and wall units

Side-draft units sit on a level concrete pad or a steel wall bracket rated for the operating weight. Leave at least 2 to 3 ft of clearance on every pad side so air can reach the media and you can pull the pad frames for service. Keep the intake away from dryer vents, pet runs, dusty gravel and trash bins.

Install the roof jack, duct drop and diffuser

The roof jack is the sheet metal transition that carries air from the cooler's discharge through the roof deck. Under it, a duct drop runs through the attic to a ceiling diffuser. Single-drop residential installations commonly use a square drop in the 16 x 16 in to 20 x 20 in range, depending on cooler size, and larger or branched systems are sized for velocity as described in ductwork for evaporative coolers.

1. Locate the opening from the attic. Drive a nail up through the roof at the center of the planned opening, between framing members, then mark it from above.
2. Cut and flash. Cut the deck, set the roof jack or curb, and flash it into the roofing so upslope shingles lap over the flashing. On flat roofs, flash into the membrane using the roofing manufacturer's method.
3. Build the drop. Connect the jack to the ceiling opening with galvanized duct, framed opening at the ceiling, and seal joints with foil tape or mastic.
4. Insulate. Wrap the drop in the attic with duct insulation (R-6 to R-8 is common). Attic air can top 130 F and will otherwise heat the supply air.
5. Set the diffuser. Install a ceiling diffuser with adjustable louvers and, ideally, a closable damper or insulated winter cover.
6. Mount the cooler. Set the cooler on its stand, level it in both directions, align the discharge over the jack, and seal the connection with a canvas or flexible collar to keep vibration out of the ductwork.

Run the water supply and drain

A whole-house cooler typically evaporates about 3 to 15 gallons per hour plus bleed-off, so the supply line is small: 1/4 in OD copper or poly tubing from a cold water line is standard. Put a quarter-turn shutoff valve somewhere you can reach in winter, ideally indoors, and slope the line so it can be drained. Avoid self-piercing saddle valves; they are the most common source of slow leaks technicians find in attics.

At the cooler, the tubing connects to the float valve with a compression fitting. Set the float so the water level sits roughly 1/2 to 1 in below the overflow. Then route two outlets:

Overflow drain

A standpipe fitting in the pan that carries away water if the float sticks. Pipe it to the roof edge, gutter or an approved drain, not onto shingles.

Bleed-off line

A small continuous discharge (or a timed purge/dump valve) that removes mineral-laden water. Expect bleed-off to add roughly 25 to 100 percent to evaporation depending on hardness.

Bleed-off settings are covered in bleed-off and water quality.

Wire the cooler and control

Residential coolers with 1/3 to 1 hp motors usually run on 120 V. A whole-house unit should have its own circuit, sized to the motor and pump nameplate amps and local code, with a disconnect within sight of the cooler. Many inspectors also expect GFCI protection for equipment and outlets on the roof or outdoors. This is work for a licensed electrician in most jurisdictions.

Control options range from a rotary switch (off, pump, low, high, vent) to a low-voltage wall thermostat that drives a relay box in the cooler. Two-speed motors need a control with separate low and high outputs, and the pump should start before the fan to pre-wet the pads.

Plan relief air

An evaporative cooler pushes outdoor air into the house, so the same volume must leave. Without an exit, pressure builds, airflow drops and humidity climbs. The rule this site uses is roughly 1 to 2 sq ft of open window or relief damper area per 1,000 CFM.

First start and commissioning checklist

1. Fill and check for leaks. Open the water valve, let the pan fill, and confirm the float shuts off below the overflow. Inspect every fitting and the pan seams.
2. Prime the pads. Run the pump alone for 2 to 5 minutes (longer for rigid media) and confirm water reaches every part of the pads through the distributor or spider.
3. Open relief. Open windows or relief dampers sized as above before starting the blower.
4. Start on low, then high. Listen for belt slap, rubbing blower wheel or rattling panels. Check motor amps against the nameplate if you have a clamp meter.
5. Measure performance. After 15 minutes, measure supply air at the diffuser and outdoor temperature. A healthy system on a dry day should come close to what the cooling temperature calculator predicts for your pad type.
6. Set bleed-off. Adjust the bleed valve for your water hardness and confirm it drains where intended.

Mistakes technicians see most often

Once it is running, keep it that way with the maintenance schedule.