Evaporative Cooler

A fan, a small water pump, and a set of thick fibrous pads are the whole machine. The pump keeps the pads wet, the fan pulls outside air through them, and water evaporating off those pads takes heat out of the air. How far the temperature drops depends on how dry the incoming air already is, which engineers measure as wet-bulb temperature. Dry air carries more cooling potential, so the same unit behaves very differently in June than it does in August.

Section M1413.1 of the International Residential Code sets the install rules. The equipment has to be listed, and it goes in per the manufacturer's instructions, on a level platform a technician can reach for service, with any opening through an exterior wall flashed against water. Two more conditions matter here. The water line feeding the pads must be protected so cooler water can never siphon back into your drinking water, and the air intake has to sit away from plumbing vents and flues.

For example, a Cave Creek home with a rooftop down-draft cooler runs cheaply through the dry heat of May and June, then fades in July. Arizona's monsoon drives dew points up, and moist air cannot absorb much more water, so the pads stop delivering. That seasonal cliff is why most custom homes here treat evaporative cooling as a shoulder-season system and run a heat pump for the rest of the year.

A swamp cooler is not a cheaper air conditioner. It adds moisture instead of removing it, and it works on a single pass of outside air, so a window or a relief vent has to stay open to let that air back out. Refrigerated air recirculates and dries. Upkeep differs too: pads, float valve, and pump get serviced every spring, and the water line gets drained every fall so nothing sits standing in it.