The best evaporative coolers for large rooms are not the slim towers most listings push under the same name. An evaporative cooler, also called a swamp cooler, pulls hot dry air through a water-soaked pad and blows out air that can be 5 to 15 degrees cooler in dry weather. A 300 square foot tower cannot do that for a 1,500 square foot living room, no matter how many settings it has on the panel. If you have been reading our general evaporative cooler picks, you will notice this roundup deliberately skips most of them.
What actually matters in a large room is airflow volume, measured in CFM, or cubic feet per minute. A bedroom unit pushes 900 to 1,800 CFM. A room that feels genuinely cooler usually needs 3,000 CFM and up, and garages, workshops and open-plan living spaces want even more. We lined up ten units from 900 CFM to 11,000 CFM, checked the published noise ratings, tank sizes and real customer complaints, and ranked them by what they do in a big open space.
One caveat first, because it decides whether any of this works for you. Evaporative cooling adds moisture to the air. In a dry climate, with a window or door open and a second opening for humid air to escape, that moisture is cheap air conditioning. In a humid climate the same unit makes a room muggy and you should spend your money elsewhere. We also run on standard 120 volt power, not a dedicated circuit, so you avoid the install cost of a mini-split.
Our ranking favors published CFM, tank capacity that survives a workday, decibel ratings you can plan around, and review volume that proves the unit survives contact with real rooms. Where a listing overstates its output, we say so. Two of the ten below are honest failures for large rooms, and we explain why rather than quietly ranking them well.
Table of Contents
Top 3 Picks for Large Rooms in 2026
The Hessaire MC37M takes our top slot because it pairs real 3,100 CFM output with the largest body of customer feedback in this group, and 552 ratings tell you far more than a spec sheet can. The Uthfy 40-inch unit moves more air for less money, which makes it the value pick for patios and shops. The Hessaire MC92V is the only unit here built for a genuinely large workshop or barn at 11,000 CFM.
Best Evaporative Coolers for Large Rooms at a Glance (September 2026)
| Product | Specifications | Action |
|---|---|---|
 Hessaire MC37M |
|
Check Latest Price |
 Uthfy 40 in 4800 CFM |
|
Check Latest Price |
 SereneLife 3200 CFM |
|
Check Latest Price |
 Uthfy 4000 CFM |
|
Check Latest Price |
 OEMTOOLS 3-Speed 3100 CFM |
|
Check Latest Price |
 Hessaire DC18 |
|
Check Latest Price |
 Hessaire MC92V |
|
Check Latest Price |
 VCJ 1800 CFM |
|
Check Latest Price |
 SYUDTY 3000 CFM |
|
Check Latest Price |
 Hexago 7500 CFM |
|
Check Latest Price |
Two things stand out in that table. First, the CFM spread is enormous, from 900 to 11,000, so the word large covers very different rooms. Second, most manufacturers claim 950 or 1,000 square feet of coverage regardless of airflow, which is why buyers routinely end up with a unit that moves air around without cooling anything.
1. Hessaire MC37M: Best Overall for 950 Sq Ft Garages and Porches
- 3100 CFM for a 950 sq ft rated space
- 10.3 gallon tank with garden hose adapter
- 4 fan-only plus 2 evaporation settings
- Only 276W on a standard 115V outlet
- Noticeably loud even on the lowest setting
- Adds humidity so open windows are essential
- Open tank sloshes when you move it
This is the unit we keep coming back to, and the reason is simple: 3,100 CFM is the first airflow number in this roundup that genuinely matches the room size it claims. Owners in the desert Southwest, Texas and Florida report it cooling porches, garages and patios, including several who measured drops of around 15 degrees once the pad was soaked and the louvers were aimed into the space.
The 10.3 gallon reservoir is the quiet hero. It runs roughly six hours between fills, which covers a working day without a hose, and the included adapter lets you connect a garden hose when you want continuous unattended operation across an eight-hour timer.
Spec sheet worth noting: 276 watts on 115 volts, three speeds, oscillating vents, and a 55 dB rating. That draw is roughly what a large window fan uses, which is why it runs for pennies compared with a portable air conditioner of similar room coverage.
What 55 dB means for a shared garage
At 55 dB you can hold a conversation over it from about ten feet, which makes it acceptable in a garage or covered porch where you are working alone. It is not quiet enough for a bedroom or a meeting room, and owners describe it as the loud setting on the unit even at low speed.
Where it falls short
The recurring complaint from humid regions is that the unit blows warm air in a sealed room. It adds moisture, so it needs an open window and ideally a second opening, and a minority of owners report a musty smell that develops if the tank sits wet for days. Reviewers in humid climates like New York City say it only works as a fan without window venting.
2. Uthfy 40-Inch 4,800 CFM: Best Value for Workshops and Patios
- 4800 CFM suits garages patios and workshops
- Metal frame with copper motor build
- Four caster wheels with two lockable
- Ice packs and 4-in-1 ice curtain
- Only 103 ratings so far
- Ice chill is modest against 4800 CFM
- Top fill is awkward on a 40 inch frame
The Uthfy 40-inch is the airflow per dollar standout in this group. At 4,800 CFM it out-moves the MC37M by more than 50 percent, adds 120 degree oscillation across three fan speeds, and pulls only 200 watts. It is also the consensus category leader among the testing channels we reviewed, which tells you it is the pick most people end up with.
The 11 gallon tank holds a full working day, and the four 360 degree casters, two of them lockable, make it easy to move between a workshop and a covered patio. Fill options include a top pour and continuous auto-refill, with a drain port for winter.
Two details separate this from the tower units it is usually compared with. The frame is steel rather than thin plastic, and the motor is copper, which is why it is a reasonable choice for a shop floor where a plastic chassis would crack.
How the ice packs actually help
Three ice packs and a composite ice curtain sit in the air stream in front of the pads. The effect is a chill at close range in front of the unit that fades across a room, so treat the ice as a comfort feature for a desk or a break area rather than a room-cooling mechanism.
What to know before buying
The review base is thinner than the Hessaire at 103 ratings, and there is little written customer feedback for this listing, so sentiment comes mostly from the feature set. At 39.7 pounds, repositioning it takes two hands once the tank is full.
3. SereneLife 3,200 CFM: Best With Wi-Fi and App Control
- 50 liter detachable tank runs long between refills
- Wi-Fi with remote and a 12 hour timer
- Water shortage alarm and pump protection
- Only 80W draw
- Cooling output is inconsistent across owners
- Small casters struggle when the tank is full
- Some units shut down after an hour or two
If your priority is scheduling rather than raw CFM, this is the only model here with built-in Wi-Fi. You can start it from your phone before you walk out to the garage, run it on a programmable 1 to 12 hour timer, and the water shortage alarm protects the pump when the tank runs dry.
Airflow of 3,200 CFM is respectable for a covered outdoor space or a shop, and its 80 watt draw is at the low end of the range in this roundup. The detachable 50 liter tank works out to roughly 13 gallons, among the larger reservoirs here.
The reviews are sharply split, and that matters. Owners who like it praise the airflow, the tank and the smart controls, while a significant minority say the cooling falls short of the advertised output and that it behaves like an ordinary fan.
Should this go in an open-plan space?
At 65 dB it is one of the louder units here, closer to a standard household fan than a background appliance. Fine for a garage, a shop or an outdoor event, questionable in a room where people are trying to hear each other.
The 3.6-star problem
With 55 ratings and a 3.6 average, plus owners reporting models that switch themselves off after an hour or two and casters too small to roll a full tank, we would treat this as a feature-driven choice rather than the safest cooling buy. Reviews also span several size variants in the same family, which dilutes the signal.
4. Uthfy 4,000 CFM: Quietest Pick for Bedrooms and Offices
- 45 dB is the quietest published rating in this group
- 10 to 12 degree drops reported in enclosed rooms
- Three refill methods including a hose
- 12 hour timer with remote and ambient light
- Rated CFM runs ahead of measured output
- Pump can cut out with water remaining
- Thin plastic shell and flimsy clamps
The headline spec here is noise. That figure makes this the quietest published rating in the group, and low noise is a hard requirement for anyone cooling a converted warehouse office, which comes up constantly in HVAC advice forums.
It also carries a 13.5 gallon detachable tank, the largest reservoir among the 3,000 to 4,000 CFM models here, plus three refill methods, four caster wheels with two brakes, a 12 hour timer and a remote, plus an LED ambient light that makes it look like an appliance rather than a shop tool.
Owners who like it report measurable drops of 10 to 12 degrees in an enclosed space with the window open, which is why we still included it despite a weak aggregate score.
Is the 4,000 CFM claim real?
Probably not, entirely. Owners describe the cooling pads as thin, and say airflow drops noticeably once the media is wet, which suggests the rating is a free-air number. Budget for real performance closer to the 2,500 to 3,000 CFM range.
The 3.1-star listing explained
At 3.1 stars across 86 ratings this is a polarised product. A large share of one-star reviews report a pump that stops while the tank is still half full, cracked basins, and failure to cool a double garage as advertised, and one owner switched to a higher-CFM unit from an established brand and described the difference as night and day.
5. OEMTOOLS 3-Speed 3,100 CFM: Best Garage Cooler With Tool Storage
OEMTOOLS 23968 3-Speed Portable Swamp Cooler 3100 CFM 10.3-Gal. Water Tank
- High density media panels wick evenly
- Axial propeller spreads air quietly
- Tool tray and casters built for garages
- UL listed GFCI plug
- 68 dB noise level is the highest in this roundup
- 41 pounds is heavy to reposition
- Little written owner feedback on this listing
This one is built like shop equipment rather than home furniture. The high-density media panels claim 80 percent more evaporation surface area than standard media, a 1/5 HP three-speed motor uses knob controls instead of a membrane panel, and the integrated tool tray means your sockets are not sitting on the floor next to a puddle.
It is also the only unit in the roundup with a UL listed GFCI plug, which matters if you plan to run it outdoors or connect a hose in a damp garage. UV-resistant resin is specified for the same reason.
Note the shape: 45 by 28 by 17 inches lying low, not a tower. That keeps the discharge air near floor level, which works well in a garage where you want air moving across the work area at bench height.
Do not put this in a bedroom
At 68 dB it is the loudest unit we list and louder than a standard shop vacuum. The patented axial propeller does a good job of distributing a lot of air, but there is no version of this spec sheet that makes it a sleeping or conversation appliance.
What we could not verify
Written customer feedback is thin on this listing, so the 4.2 average across 69 ratings is the main evidence available. The same line also comes in a 5,300 CFM variant, which is the version worth stretching to if your garage is bigger than 1,000 square feet.
6. Hessaire DC18: Best Battery-Powered Cooler for Off-Grid Work
- Runs on 18V and 20V tool batteries
- Quiet strong fan for its size
- Easy to refill and simple to set up
- Owners often buy a second one
- 900 CFM is far short of a large room
- Uses water quickly in cooling mode
- 42 pounds is bigger than expected
We are including this one as a deliberate contrast. It is the smallest product here and the only one that runs on a tool battery, which makes it genuinely useful on a job site, in an auto shop with no outlets nearby, or in a trailer where mains power is not an option. It is not a large-room cooler.
Compatibility with all major 18V and 20V tool battery platforms is the whole point, and it also includes a 115V AC adapter. The 2.8 gallon reservoir refills easily and works well with ice water for extra chill.
Owners repeatedly praise the build quality for the money and the strong, quiet fan output relative to the size, and the company states plainly that this is not an air conditioner, it is designed to reduce heat stress.
Where it earns its place
Camping, job sites, trailers and small auto shops. For anything with an outlet and a room bigger than 300 square feet, the larger models in this roundup are a better use of your money.
The catch
At 42 pounds it is heavier than the size suggests, and reviewers report drinking through the 2.8 gallon tank quickly in cooling mode, so you are carrying water with you. Effectiveness also drops sharply in humid air, like every unit here.
7. Hessaire MC92V: Premium Pick for Workshops and Barns
- 11000 CFM felt 25 feet away in workshops
- Works through 100 degree outdoor heat
- Hose connection with float valve runs unattended
- About 0.05 per hour to operate
- Paper media pads smell for weeks
- 126 pounds is very heavy to reposition
- Casters struggle once the tank is full
This is the only unit in the roundup that answers the question of what cools a genuinely large open space. At 11,000 CFM owners report feeling the output up to 25 feet away, and the manufacturer states plainly that it is intended for outdoor and semi-open areas rather than sealed rooms.
The economics are the story. A 50 watt draw works out to roughly 0.05 per hour according to owners, so running it through a 100 degree afternoon in a workshop costs less than a sandwich. The direct hose connection with a float valve means continuous unattended operation with no refills.
The 33 gallon tank gives three to four hours of runtime on a fill, high-density XeL50 media claims 80 percent more evaporation surface, and independently adjustable horizontal and vertical vanes let you aim the discharge away from an open bay door rather than out of it.
What owners praise most
People running unconditioned workshops, barns and patios say it makes those spaces workable in extreme heat, and several note that pairing it with an exhaust fan and a slightly open door is what tips it from fan to cooler.
The wet-build problems
There are real ones. Paper media pads reportedly stink for weeks before the smell fades, the pump can be too weak to wet the pads evenly and leaves dry patches, the open-housing motor can rust and lock up within one or two cooling seasons, the 126 pound weight makes damage in transit common, and the casters are inadequate once the tank is full. A remote control is frequently listed but not included.
8. VCJ 1,800 CFM: Best for a Large Bedroom or Home Office
- Ready in minutes with no tools needed
- 5.6 gallon tank is large for the body
- 17 pounds with two locking casters
- Remote plus 1 to 12 hour timer
- 1800 CFM will not cool a large room
- Supplied ice packs melt quickly
- Some pumps stop after about a month
At the bottom of the airflow range, this is the pick for a large bedroom, a basement room or a home office where you need air movement and a modest temperature drop rather than whole-room cooling. Owners report it made a hot bedroom or converted garage sleepable, which is a real and specific use.
It weighs 17 pounds, has four universal casters with two locking brakes, and the 5.6 gallon tank is generous for its body. The 3-in-1 design also runs a mist mode and an aroma diffuser, and the removable washable filter and glass top are easy to clean.
One tip from owners is worth repeating: freeze solid ice blocks in your own containers rather than relying on the four soft ice packs included, which melt quickly.
Is 1,800 CFM enough?
For a bedroom with an open window, often yes. For a 900 square foot living room, no. At 1,800 CFM this sits near the bottom of the airflow range here, and that number is the one most often confused with large-room capability in online listings.
What the 18 ratings show
The sample is small, which is the main caution. Positive reviews describe quick assembly, strong airflow and good value, while negative ones mention pump failures after about a month and build details that did not match the listing photos.
9. SYUDTY 3,000 CFM Swamp Cooler: Best Budget Pick With Wheels and a Long Timer
Portable Air Conditioner, 3000 CFM Swamp Cooler & Evaporative Air Cooler
- 15.7 pounds with swivel casters and a carry handle
- 1 to 15 hour timer and 20 foot remote
- Four modes including sleep mode and a child lock
- Adds moisture which suits arid rooms
- 3.2 star average with 26 percent one star
- Output falls once the high density pad is wet
- Manufacturer temperature claims far exceed what owners see
This has the most customer ratings in the roundup at 243, which makes it the best place to read what actually happens with a mid-size unit over time. At 15.7 pounds it is also the easiest to carry between rooms, with four 360 degree swivel casters and a hidden handle.
Feature-wise it is generous: 3,000 CFM, a 6.87 gallon tank, a 1 to 15 hour timer with a 20 foot remote, four modes including sleep, a child lock and a 2.5x cooling curtain.
What the ratings reveal is the split. Forty-one percent of ratings are five stars and 26 percent are one star, which is a hit-or-miss distribution rather than a consistent product.
Read the manufacturer temperature claim carefully
The listing claims rapid ambient temperature drops of 50 to 60 degrees, which no evaporative unit in any climate can deliver to a large room. Treat that as marketing language, and judge the unit on airflow and humidity instead.
Who should skip it
If you need a unit you can rely on in a large living room, the 3.2 average and the reported drop in output once the high-density pad is wet argue for stepping up to the MC37M or the Uthfy instead. For a bedroom or a den at modest cost, it is a reasonable gamble.
10. Hexago 7,500 CFM: Best for Patios With Long Timer Control
- Three panel intake spreads air evenly
- 13.2 gallon tank with hose hookup and level window
- ETL safety listed with a water shortage alarm
- 24 hour timer suits long shop days
- One owner measured about 1900 CFM against the claim
- Touch controls often unresponsive at power up
- Only 15 ratings to judge it on
The 24 hour timer is the standout feature here, letting you schedule a full day without resetting it. The three-panel intake with 120 degree oscillation and both horizontal and vertical swing is designed to spread air across a wide covered patio or shop bay.
It also carries an ETL safety listing, and the audible water shortage warning protects the pump. The 13.2 gallon tank takes a top fill, a garden hose connection, and the level window means you can see the water without lifting the lid.
Owners in moderate heat report the cooling is genuinely felt on back porches and patios in 80 to 90 degree weather, and one detailed reviewer praised the chassis, dust screens and internal drip trays that cut splashing noise.
The measured CFM problem
One reviewer measured airflow at roughly 1,900 CFM against the 7,500 CFM claim, a shortfall of about 75 percent. Rated CFM on a portable cooler is a free-air figure, and this is the clearest published example of how far that number can drift.
Two practical warnings
The unit must sit level or the pads wet unevenly and cooling stops, and the touch buttons are often unresponsive for the first several minutes after power-up. With only 15 ratings, treat this as a considered purchase for a patio rather than a safe default.
How Much CFM Do You Need? The Sizing Formula
Advertised coverage in square feet is the least reliable number on a cooling listing, because most manufacturers print 950 or 1,000 square feet on everything from a 1,800 CFM tower to a 7,500 CFM unit. Use airflow instead, with the sizing method below as your starting point.
Multiply the floor area in square feet by the ceiling height in feet, then divide by two. A 1,000 square foot room with 8 foot ceilings needs about 4,000 CFM. A 2,000 square foot room with 8 foot ceilings needs about 8,000 CFM, which is where portable units run out and whole-house systems start.
From that number, use a short list to choose. Up to about 400 CFM per 100 square feet handles a small room. Around 500 CFM per 100 square feet suits a 900 to 1,200 square foot living space. Anything above that points to the workshop and outdoor class, and above 1,500 square feet indoors you should be pricing a ducted or whole-house system rather than a portable unit.
Match the tier to the room, and use our commercial evaporative cooler roundup if you are cooling a warehouse or shop floor rather than a living space.
Where to Put the Unit and How to Run It
Placement decides whether the unit is a cooler or a fan. Put it near an open window or door on one side of the space, and open a second opening on the far side so the humid air has somewhere to go. With both ends open, the continuous flow of dry outside air is what lets evaporation work at all.
Keep curtains, rugs and clutter away from the intake pads, because blocked intake is the most common reason a unit blows warm air. Leave clearance on the discharge side so the cool air travels across the room instead of along the ceiling.
Run it on high for the first fifteen to twenty minutes to soak the pads fully, then step down to a lower speed. As a rough rule of thumb, evaporative cooling works well up to about 100 degrees of outdoor temperature, and the drop in the room falls as humidity climbs.
What It Costs to Run
Evaporative cooling is far cheaper to run than air conditioning because it replaces a compressor with a fan and a pump. The units in this roundup draw between 50 and 276 watts, and one high desert user reported running central air constantly to hold 76 to 78 degrees with a 450 monthly bill, while their swamp cooler held 77 to 80 degrees in the same house.
The catch is water. A large unit burns roughly 3.5 to 10 gallons per hour, so a workday of running means either a hose connection or refills. The units with hose hookups and float valves are the cheapest to operate over a full season, because the water cost is trivial next to the labour of refilling by hand.
Home improvement guides put electricity savings at up to 75 percent less than running an air conditioner, and the wattage figures on these listings support that claim. If you also need heat in the winter, our space heater picks for large rooms cover the other half of the year.
When Not to Buy an Evaporative Cooler
Several situations make this the wrong purchase, and saving money here means spending it in the wrong place. If you live in a humid climate, the unit raises the humidity in the room instead of lowering the temperature, and a dehumidifier plus a fan is the better pairing. If you need to cool a sealed bedroom with no open window, it cannot work, because the supply of dry air has to come from outside.
If you need quiet, treat 45 dB as the practical floor. Anything at 55 dB or above will compete with conversation and sleep, and the loudest models in this roundup sit at 65 and 68 dB. If your room is above 1,500 square feet and fully enclosed indoors, no portable unit will hold it, and a ducted or whole-house system is the honest answer.
The blunt negative experience is worth hearing too. Owners who moved to the Southwest from a humid region often find the experience disappointing, and that reaction is the standard one from people who tried a cooler in the wrong climate. Check your humidity before you order, not after.
Maintenance: Pads, Mold and Winter Storage
Mold and the swamp smell are the two complaints that follow every one of these products, and both come from the same cause, standing water. Run the fan only for 30 to 60 minutes after you switch off the pump so the pads dry, and avoid letting a cooler sit wet for long stretches.
Change the cooling pads at least twice a season. Fiber pads are cheaper and need replacing more often, while rigid media pads cost more and last for years, and that is the single biggest factor in how much you spend on consumables.
Before winter, drain the tank completely, hose the pads, wipe down the basin to remove mineral buildup, and disconnect and cover the unit. A single missed drain-down is what produces the smell users complain about the following spring.
One more safety note. If you run a unit outdoors or connect a hose in a damp space, use a GFCI-protected outlet. Only the OEMTOOLS 3,100 CFM in this roundup comes with a UL listed GFCI plug, so for the rest a GFCI adapter is worth adding to your setup.
Frequently Asked Questions
What is the best air cooler for a large room?
For a 900 to 1,000 square ft garage, porch or living space, the Hessaire MC37M is the strongest all-round pick at 3,100 CFM, 55 dB and a 10.3 gallon tank. For a workshop or open patio, the Uthfy 40-inch moves 4,800 CFM for less. For spaces above 1,500 square ft, only the 11,000 CFM Hessaire MC92V or a ducted system is realistic.
Is there a difference between a swamp cooler and an evaporative cooler?
No. The two names describe the same appliance. A swamp cooler is the common term, and evaporative cooler is the formal one used in manufacturer specifications. Both use a fan, a pump and a wet media pad instead of a refrigerant compressor, which is why both need open windows and dry air to work.
Can a swamp cooler work in 100 degree weather?
Yes, as long as the air is dry. The common rule of thumb is that evaporative cooling works well up to about 100 degrees of outdoor temperature, provided you have a window or door open on the inlet side and a second opening for humid air to escape. In humid weather the temperature drop shrinks and the added moisture can make the room feel worse.
What is a downside of evaporative cooling?
It raises humidity, it needs an open window to work, and it consumes real amounts of water, roughly 3.5 to 10 gallons per hour on larger units. It also does not dehumidify, so in a humid climate it can make a room muggy instead of comfortable. Add a wet pad and standing water to the list and maintenance becomes a real task.
What size swamp cooler do I need for 2000 square feet?
Multiply the floor area by the ceiling height, then divide by two. A 2,000 square ft room with 8 foot ceilings needs roughly 8,000 CFM, which is beyond what any portable unit in this roundup can hold indoors. For that size, budget for a ducted or whole-house evaporative system rather than a portable unit.
Are swamp coolers worth the money?
In a dry climate with open windows, yes, because a 50 to 276 watt fan and pump costs a fraction of a compressor to run and avoids the install cost of a mini-split. They are not worth it in a humid climate, in a sealed room, or if you need a temperature below what a wet pad can deliver. One high desert user reported a swamp cooler holding 77 to 80 degrees against 450 a month for central air.
Do evaporative coolers actually cool the room?
They cool the air, not the room, and the distinction matters. Expected drops in dry air are roughly 5 to 15 degrees, and individual owners report figures in that range, such as around 15 degrees on the Hessaire MC37M and 10 to 12 degrees on the Uthfy 4,000 CFM. Sealed rooms see far less, because the pad has no fresh dry air to work with.
Is it cheaper to run a swamp cooler or AC?
Much cheaper, by a wide margin. The units here draw between 50 and 276 watts, and guides put evaporative cooling at up to 75 percent less electricity than running an air conditioner. The trade is water and effort, since a large unit uses roughly 3.5 to 10 gallons per hour unless you connect a garden hose.
Our Final Recommendation by Room Size
For a garage, porch or living space up to about 1,000 square feet, the Hessaire MC37M is the evaporative cooler we would buy first, because 3,100 CFM, a 10.3 gallon tank and 552 ratings make it the least risky of the ten. Push into workshop territory and the Uthfy 40-inch at 4,800 CFM moves more air for less money, while the 11,000 CFM Hessaire MC92V is the honest answer for barns and semi-open industrial spaces.
Check your humidity before anything else. If the air is already humid, or the room has no open window, save your money and look at a portable air conditioner instead. If the air is dry and you can leave a door open, the best evaporative coolers for large rooms in 2026 will cool a large space for a fraction of the running cost of the air conditioner you were about to install.