Types of home cooling, and what each one actually does

The single most useful distinction in home cooling is not price or brand. It is whether a device removes heat from the room or merely moves air around inside it. Almost every wasted purchase in this category comes from buying something in the second group while expecting the first.

A fan changes nothing on a thermometer. Its motor adds a small amount of heat to the room, so strictly it makes the room very slightly warmer. What it does is move air across your skin, which speeds evaporation of sweat and carries away the warm boundary layer sitting against you. The effect is worth several degrees of perceived temperature, which is not nothing — it is most of what people want.

Two consequences follow. A fan in an empty room is doing nothing at all — there is no one for it to cool. And above roughly 95°F a fan can stop helping, because moving air that is hotter than your skin adds heat faster than the extra evaporation removes it.

Within that limit they are extraordinarily cheap. A ceiling fan on low draws under 2 W — about 7.9¢ for a month of nights. A good DC tower fan is 19 W flat out. Even a 20-inch box fan on high is about $4.49 a month.

Where each type fits: tower fans for a bedroom footprint, box fans for maximum air per dollar, window fans when the outside air is cooler than the inside air, and ceiling fans if you have somewhere to hang one — they are the cheapest cooling that exists.

A swamp cooler pulls air through a wet pad. Evaporating water absorbs heat, so the air coming out is genuinely colder than the air going in — this is real cooling, not a perceived effect, and it costs about a fifth of what refrigeration costs. The Honeywell CO60PM moves 2,697 CFM on 220 W.

The condition is absolute: the air has to be dry enough to accept the moisture. In Phoenix in June that trade is excellent. In Houston the air is already close to saturated, there is almost no evaporation available, and you end up with air that is barely cooler and noticeably damper — which feels worse, not better.

They also need somewhere for the humid air to go, so an evaporative cooler wants an open window or door. That makes them ideal for a garage with the door up or a patio, and poor for a sealed bedroom. The humidity threshold is here.

Every air conditioner runs the same cycle: absorb heat from the room on the cold side, reject it somewhere else on the hot side. The categories differ only in where the hot side is, and that turns out to determine almost everything about efficiency.

Window and through-the-wall units

The hot side is outside, in the wall. This is the efficient configuration and the data shows it: a certified 8,000 BTU window unit uses 375 kWh a year — about $69 at 18.34¢/kWh — for a whole cooling season. They are ENERGY STAR certified with published CEER and annual kWh figures, so you can compare them on tested numbers rather than marketing. The picks are here.

Portable units

The whole machine is inside the room and the heat leaves through a duct. That duct is hot and it is in the space you are cooling, and a single-hose unit also blows room air outside — which is replaced by hot outside air infiltrating in. The DOE test procedure accounts for both, which is why a portable’s SACC rating is well below its box BTU. They are the right answer only when a window unit will not physically fit.

Mini-splits

The compressor lives outside and only refrigerant lines pass through the wall, which is the best of both worlds: high efficiency, very quiet indoors, no window occupied. The catch is installation — this is licensed work involving refrigerant handling, and the install cost typically exceeds the equipment cost. It is the right answer for a permanent solution in a room you own.

These are fans, so they cannot cool below the outdoor temperature. What they do is exchange air: a whole-house fan pulls cool outdoor air in through open windows and pushes hot indoor air out through the attic, dumping the day’s accumulated heat in minutes rather than hours. An attic fan does the same for the attic alone, reducing heat radiating down into your ceilings.

The condition, again, is absolute: your nights have to get genuinely cool. Where they drop into the 60s, a whole-house fan can replace air conditioning for a large part of the season. Where they stay in the 80s it is an expensive way to move hot air around. The temperature test is here.

Both involve cutting a ceiling or working in an attic with wiring. That is licensed-professional work, and we say so wherever it comes up.

1. Does the room need to be colder, or do you need to feel cooler? If a fan on a hot day is enough, buy a fan and stop. It is a hundredth of the running cost.
2. Is your air dry? If summer humidity is routinely below about 40%, an evaporative cooler gives real cooling for a fifth of the power. If it is not, skip the category entirely.
3. Do you have a usable window? If yes, a window unit is cheaper to buy, cheaper to run and quieter in the room. If no, a portable is the compromise — or read this if there is no window at all.
4. Do your nights get cool? If they do, a whole-house fan or even just a window fan run as an exhaust may do most of the work for a fraction of the cost.

Most people, most of the time, are best served by a layered answer: a fan for the majority of the season, blinds closed during the day, and a correctly-sized window unit for the two or three weeks when the fan is genuinely not enough. The bedroom page works that sequence through in order.