Hessaire MC37 Review: Real Cooling in Dry Heat, a Damp Fan Elsewhere

The Hessaire MC37 evaporative cooler is the portable swamp cooler we'd roll into a garage, shop or patio in the dry West, and the one we'd tell anyone in a humid summer to skip. It cools by evaporating water into the air, so it only works when that air is dry. On a 10% humidity afternoon it can blow air 20-plus degrees cooler than the day. In muggy weather it's a big fan that makes the room damp.

Hessaire rates it at 3,100 CFM with a 10.3-gallon tank, three fan speeds, oscillating louvers and a 250 W draw. That airflow figure is Hessaire's own, so treat it as a maker claim. The MC37M and MC37V are essentially the same cooler with different control panel and motor part numbers, so buy whichever an authorized seller has for less.

One buying note. The Amazon listing we link is sold by a third-party seller, not Hessaire, and Hessaire's warranty covers only coolers bought from Hessaire or an authorized seller. We couldn't confirm whether that seller is authorized. Keep your receipt and the serial number either way, because a claim needs both.

What it does well

• Cheap to run: 250 W on Hessaire's spec, roughly a third of what a 10,000 BTU window AC pulls while cooling (our estimate from that unit's efficiency rating).
• Lots of air for the money: a 3,100 CFM rating, three speeds and swinging louvers, built for garages, patios and shop floors.
• Easy to keep running: Hessaire sells the pump, float valve kit, media set and control panel as separate parts.
• Hose hookup: a float valve and garden hose adapter keep the 10.3-gallon tank topped up outdoors.

Where it falls short

• Humidity: Hessaire says it loses effectiveness above 60% relative humidity, and its best band is 10-30%.
• It needs fresh air: run it in a closed room and it saturates the air and stops cooling. It needs an opening to pull from and another to exhaust through.
• It adds moisture: everything near it gets damper, which matters in a garage full of bare steel.
• A thin warranty: one year on parts only, with the pads and all labor excluded.

Check your humidity before you check the price

An evaporative cooler can't cool air below its wet-bulb temperature, the temperature a wet thermometer reads as water evaporates off it. How close it gets depends on the pads. The University of Florida's extension guide puts a well-designed pad system at up to 85% of the way to wet bulb, and a Building America report for DOE puts older thin-pad coolers at 50% to at most 80% and a good direct cooler at 85%. Hessaire doesn't publish a figure for the MC37, so we ran the numbers at 70% and 85%.

That's our arithmetic from standard psychrometric math at sea level; at Phoenix or Denver elevation the wet bulb runs a little lower, which helps. Read it this way. At 10% humidity you get air 24-29 degrees cooler than outside, and that's real relief. At 50% you get 11-14 degrees, but the air coming at you is close to saturated. At 70% it's 6-8 degrees of muggy breeze. Hessaire's own guidance lines up: best performance at 10-30% humidity, good at 30-50%, reduced above 60%, with a typical drop of 15-25°F.

Check the humidity at the hour you'd use it, not the daily average. In Phoenix, owners get good use out of them until monsoon moisture arrives, and some give up on them until fall. A cheap hygrometer in the garage settles the question in a week. The same Building America report gives a rule of thumb for whole climates: places where the 1% design wet bulb is 70°F or lower can be cooled comfortably with direct evaporative coolers, and up to 75°F works for many people.

The Department of Energy's consumer guide, now offline, was blunt about portables: coolers on wheels provide "only a slight cooling effect" and are "limited by the humidity within your home." That's the case for the MC37 as a spot cooler, aimed at you while you work, rather than a way to cool a whole house. If your summers are humid, buy an air conditioner. Our Midea U window AC review covers the quiet inverter unit we would start with.

The numbers Hessaire publishes

Treat the CFM line the way you'd treat horsepower on a shop vac. It's the maker's number, measured the maker's way. Portacool rates its APEX 500 at 800 CFM for 500 square feet, and Honeywell's spec sheet lists 470 CFM for a cooler whose Amazon title says 745 CFM, with an asterisk the listing never explains. Comparing CFM claims across brands tells you very little.

MC37M or MC37V?

Hessaire's current manual describes both with the same rotary fan switch, pump switch and swing switch. The M uses its own control panel and fan motor and adds a separate main power switch; airflow, tank and media are the same. Neither has a remote or a timer. Those belonged to the older MC37A, which Hessaire no longer lists, so ignore any listing that promises an 8-hour timer on an MC37M. The MC37V is a fine buy if it's cheaper; it's also sold by a third-party seller on Amazon.

Set it up so it can breathe

Hessaire's manual says the MC37 is "highly recommended for outdoor use." Indoors, it wants the cooler in front of an open window or door so it pulls fresh air, plus another opening for the room's air to leave. That second opening is the part people skip. With nowhere for the damp air to go, a room's humidity climbs within the hour and the cooling fades.

The old DOE guide gave a sizing rule for whole-house coolers: 1 to 2 square feet of opening for every 1,000 CFM, on the side of the house away from the wind. Applied to the MC37's rating, that's 3.1 to 6.2 square feet. A 16-foot garage door raised 3 to 4 inches gives you 4 to 5.3 square feet. Open it too far and hot air pours back in; too little and humidity builds.

• Best spot: in a doorway or right behind an open window, so the air entering the pads is outdoor air.
• Fill by hand indoors: the manual says continuous fill isn't to be used indoors or left unattended, so the hose hookup is for outdoor use.
• Point it at people: a portable cooler does its best work as a breeze aimed at you on the bench, not as a whole-garage chiller.
• Skip the ice: Hessaire says not to put ice in the main tank unless the model is designed for it, and the MC37 manual doesn't call for it.
• Don't hose the pads while it runs: the manual says that can damage the motor and voids the warranty.

Living with it: water, pads, pumps and rust

Plan on a lot of water. Hessaire publishes no gallons-per-hour figure, but its support page says to refill every 4 to 8 hours in hot, dry weather, and an Amazon listing claims 3 to 4 hours per tank. One eastern Oregon owner watched several gallons disappear in about an hour at 100-plus degrees. Outdoors, run the hose. Indoors, budget a bucket trip or two per session.

Pads are a consumable. Hessaire says to replace the media at least once a season, and the old DOE guide recommended twice a season to monthly for coolers that run constantly. The warranty doesn't cover them. The routine that keeps them from smelling is simple: drain and refill the tank weekly, wipe it with mild soap monthly, run vinegar through it now and then as the manual suggests, and at shutdown run the fan with the pump off for 30 minutes so the pads dry.

The pump is the part that wears. Hessaire's own troubleshooting page says pumps can wear out after 4 to 6 months of use, and the replacement is a part Hessaire sells on its own. One MC37V owner's controls stopped working, and support didn't answer their email. That's a single report, but it's a reminder that the warranty ships a part and leaves the labor to you.

The added moisture has a cost. In a garage full of tools, a swamp cooler can leave bare steel rusting and lumber moving. If you keep cast iron or a table saw out there, crack the big door wider, run the cooler only while you're working, and wipe down machined surfaces.

How it compares

Here's the MC37 against its smaller and bigger siblings, two other portables sold on Amazon, and the window AC we'd buy instead in humid country. Figures are the makers' or their listings', except the AC's power draw, which is our estimate.

• Hessaire MC18 and MC61: the same design in smaller and bigger sizes. The MC18 suits a single work area; the MC61 is for big garages and patios. Both had used offers in Amazon's buy box when we checked, so we don't link them.
• Honeywell CL201AE: a smaller indoor cooler with a remote and a carbon dust filter. Its spec sheet rates 470 CFM and 280 square feet; fine for a dry bedroom, too small for a garage.
• Portacool APEX 500: the commercial-grade choice: Wi-Fi controls, a 53 dB rating, a 13-gallon reservoir and a 3-year components warranty with a lifetime housing. It costs a lot more than the MC37.
• A window AC: removes heat and moisture instead of trading one for the other, works with the room closed and works in any climate. It draws more power, but it's the only one here that cools a humid room.

The old NREL fact sheet put the trade plainly: evaporative coolers use less than a third of the energy of air conditioners, and a room-sized unit can lower a single room's temperature 5 to 15 degrees. Both figures assume the dry climate these coolers are built for.

Who should buy the MC37

Buy it if you live where summer afternoons run under about 30% humidity, you need to work in a garage, shop or on a patio, and you can leave a door or window open while it runs. Set it in the doorway, aim it at yourself, keep the tank clean and expect to replace pads every season and a pump now and then. For that job, it's a cheap way to make 105°F bearable.

Skip it if your summers are humid, if the space has to stay closed up, or if the garage holds tools and wood you don't want damp. In any of those cases, the money goes further on a window AC or a small mini-split.