Buying guide
Evaporative coolers, and when they actually work
They cost a fraction of what refrigerated air costs to run, and for a good part of the year they work beautifully. Here is the honest version of when that is, and what to buy.
The number
One number decides whether it works
An evaporative cooler pulls outside air through a wet pad. Water evaporates, that pulls heat out of the air, and cooler air comes through the other side. Everything about owning one follows from how much moisture the outside air is already carrying.
Below about 40 percent relative humidity, an evaporative cooler does exactly what you bought it for. Between 40 and 50 you still feel it working. Above 50 the drop is obvious, and by around 60 percent the air is close enough to saturated that evaporation nearly stops and you are running a fan that adds damp to the room.
This is not a quality problem and no brand is exempt from it. It is the physics the machine runs on. Anyone selling you an evaporative cooler that works in any weather is selling you a fan.
- Under 40%Working as designed
- 40 to 50%Still effective
- 50 to 60%Noticeably weaker
- Over 60%Essentially a damp fan
The calendar
When to run it, and when to stop
The National Weather Service dates the monsoon June 15 to September 30, and the storms usually peak between mid-July and mid-August. That is your off switch. The dry stretch before it, roughly March into the middle of June, is when an evaporative cooler earns its keep, and there is a second usable window in the fall once the moisture clears out.
Plenty of Valley houses run both machines. Evaporative through the spring, refrigerated air once the dew point climbs, then back again in October. That is not indecision. It is using each one in the weather it was built for, and it is where the savings actually come from.
If you only want one machine and you need it to work in August, buy refrigerated air. We will tell you the same thing standing in the store.
The options
Three kinds, three different jobs
Which one you need depends on whether you are cooling a room, a side of the house, or all of it.
Portable
Wheels, a tank and a plug. Cools the space you are standing in. Good for a garage, a workshop or a covered patio. Fill it yourself or run a hose to it.
Window
Sits in a window opening and handles a room or two. Water comes from a plumbed line rather than a tank, so it is not something you are refilling by hand.
Whole house
Roof or exterior wall, ducted through the house. The real installation, and the one that replaces running the air conditioning all spring.
Sizing
Work out the CFM before you shop
Evaporative coolers are rated in CFM, the cubic feet of air they move every minute. The rule that has held up for decades is to multiply your square footage by your ceiling height, then halve it. A 1,600 square foot house with 8 foot ceilings is 12,800 cubic feet, so you are shopping for roughly 6,400 CFM.
That is aiming for a complete change of air about every two minutes, which is what this kind of cooling needs to do. It is not like sizing an air conditioner, where going too big causes its own problems. Here it is undersizing that people regret.
Bring us your square footage and your ceiling height. That is genuinely all we need to point you at the right unit.
The common mistake
The air has to have somewhere to go
This is the one people get wrong, and it is why somebody's cooler seems broken when nothing is actually wrong with it. A refrigerated system recirculates the same air. An evaporative cooler does not. It pushes a continuous stream of outside air into the house, and that air has to leave.
So you open windows. Not all of them and not evenly. Open them on the far side of the rooms you want cool, a few inches each, and you draw the cool air across the house on its way out. Close the house up and the pressure builds, the airflow stalls, and the rooms get humid and stuffy while the machine runs perfectly well.
A rough target is two square feet of open window for every 1,000 CFM. On a 6,000 CFM unit that is around 12 square feet of opening, spread across the rooms you actually use.
Living with one
Pads, water, and what our water does to them
There are two kinds of pad. Aspen is the loose fiber type, cheap, and generally replaced every season. Rigid media is the thick corrugated block, costs more, cools a little better and lasts several years. Either is fine. The difference is how often you want to be up on the roof.
Valley water is hard, and that is what actually kills these machines. Minerals left behind as the water evaporates build up on the pads and in the reservoir until airflow drops and the pump starts to struggle. A working bleed-off, which continuously dumps a small amount of water instead of recycling all of it, is the single best thing you can do for the life of the unit.
Then winterize it. Drain it, shut the water line off and cover it. A cooler left wet through a Valley winter is a cooler that needs a new pump and a new pan in the spring.
- Aspen padsCheap, replace each season
- Rigid mediaCosts more, lasts years
- Bleed-offNot optional in hard water
- WinterizeDrain, shut off, cover
- We stockHessaire and MasterCool, plus pads and pumps
Common questions
Before you come in
Will an evaporative cooler work in August?
Not well. Once the monsoon pushes humidity past about 60 percent, evaporation nearly stops. Run it in the dry stretch from spring into mid-June, and again in the fall.
Is it cheaper to run than air conditioning?
Considerably, because you are paying for a fan and a small pump instead of a compressor. That is the whole reason people run one through the spring.
Do I have to leave windows open?
Yes. The air has to have an exit or the system stalls. Around two square feet of opening for every 1,000 CFM.
How big a unit do I need?
Square footage times ceiling height, divided by two. That gives you the CFM to shop for. Bring us both numbers and we will do it with you.
How much water does one use?
It varies with the heat and how hard the unit is working. The more useful question is bleed-off, which wastes a little water on purpose and saves the machine from mineral scale.
Can I run it at the same time as my air conditioning?
No. They work against each other. Plenty of Valley houses switch between the two by season, which is where the savings come from.
Tell us what you are after
Ask us about it
Send a photo of the wall, the patio or the cooler on the roof and we can tell you what fits before you drive out. No pressure and no sales call rota — you get an answer from the people behind the counter.
- We answerDuring store hours, by whichever way you got in touch
- We stockMost of what we sell, so you can take it home the same day
- We installOur own crew, across Mesa and the East Valley
Pads, pumps and floats are on the shelf.
We carry Hessaire and MasterCool, and we keep the parts for what we sell. East Main between Ellsworth and Crismon.