Summer heat isn’t just uncomfortable—it’s dangerous. Heat exhaustion. Sleep deprivation. Productivity crashes. Pets and elderly family members suffering in sweltering homes.
Central air conditioning is the gold standard, but it’s expensive to install and not an option for renters or older homes. That’s where portable and window AC units come in.
Choosing the right air conditioner means understanding BTUs, energy efficiency, installation requirements, and what actually works in your specific space. Get it wrong and you’ve spent hundreds on a unit that can’t cool your room or costs a fortune to run.
We’ve analyzed hundreds of air conditioners to help you navigate the options and find what genuinely solves your cooling needs.
How Air Conditioners Actually Work
Air conditioners don’t “add cold air”—they remove heat from your space and dump it outside.
Inside your room, refrigerant absorbs heat from the air. That heated refrigerant gets compressed, travels to the outdoor component (or exhaust hose), and releases the heat outside. The cooled refrigerant cycles back to repeat the process.
A fan blows your room’s air over the cold evaporator coils. Heat transfers to the refrigerant. Cooled air returns to your room.
This process also removes humidity as a side effect. When warm air contacts cold coils, moisture condenses out—same principle as your cold drink sweating on a hot day.
The heat has to go somewhere. Window units and portable ACs exhaust it outside. That’s why they need windows or venting. “Ventless” air conditioners don’t exist—if it doesn’t vent heat, it’s an evaporative cooler, not an air conditioner.
Types of Air Conditioners Explained
Window Air Conditioners
Mount in a window opening. Part sits inside, part sits outside. Most efficient design because hot and cold sides are completely separated.
Pros: Most efficient cooling, lower energy costs, don’t take floor space, effective cooling
Cons: Semi-permanent installation, blocks window use, visible from outside, challenging to install alone
Portable Air Conditioners
Freestanding units that sit inside your room. Hot air vents through an exhaust hose you run to a window.
Pros: No installation, move room to room, easy to store off-season, renters can take them when moving
Cons: Less efficient, take floor space, hose must vent outside, some models noisy
Through-the-Wall Air Conditioners
Similar to window units but designed to mount in a wall sleeve. Permanent installation.
Pros: Don’t block windows, more secure than window units, cleaner look
Cons: Requires wall modification, semi-permanent, professional installation often needed
Mini-Split Systems
Indoor unit mounts on wall, connects to outdoor compressor unit via refrigerant lines through a small wall hole.
Pros: Extremely efficient, very quiet, no ductwork needed, heat pump versions provide heating too
Cons: Higher upfront cost ($1000-3000+), professional installation required, visible indoor unit
Evaporative Coolers (Swamp Coolers)
Use water evaporation to cool air. Not true air conditioners.
Pros: Much cheaper to run, no exhaust required, add humidity (good in dry climates)
Cons: Only work in low humidity (<40%), add moisture (bad in humid climates), less cooling power
BTU: The Number That Determines Everything
BTU (British Thermal Units) measures cooling capacity. Higher BTU = more cooling power.
Too little BTU and your AC runs constantly without cooling properly. Too much BTU and it cycles on and off rapidly, never running long enough to dehumidify properly, wasting energy.
Room Size Rough Guide:
- 150-250 sq ft: 6,000 BTU
- 250-350 sq ft: 8,000 BTU
- 350-450 sq ft: 10,000 BTU
- 450-550 sq ft: 12,000 BTU
- 550-700 sq ft: 14,000 BTU
But square footage alone doesn’t tell the whole story.
Add BTU if:
- Room is heavily shaded: -10%
- Room receives strong sun: +10%
- More than 2 people regularly occupy the space: +600 BTU per additional person
- Kitchen (heat-generating appliances): +4,000 BTU
- High ceilings (over 8 ft): Multiply square footage by ceiling height in feet, then divide by 8
Example: 300 sq ft bedroom, south-facing with full sun, 9-foot ceilings, two people sleeping
Base: 8,000 BTU
Sun exposure: +800 BTU
High ceiling: 8,000 × 1.125 = 9,000 BTU
Result: You need closer to 10,000 BTU, not 8,000
The Portable AC Efficiency Problem
Portable air conditioners are convenient but less efficient than window units—sometimes dramatically less.
Single-hose portables pull room air, cool it, use some to cool the compressor, then exhaust that air outside. This creates negative pressure, pulling hot air back into your room through every crack and gap.
Dual-hose portables are better—one hose pulls outside air to cool the compressor, one hose exhausts heat. No negative pressure issue. But they’re bulkier and more expensive.
A 10,000 BTU portable AC often cools like an 8,000 BTU window unit due to this inefficiency.
The Department of Energy changed portable AC ratings in 2017, introducing “SACC” (Seasonally Adjusted Cooling Capacity)—a more realistic measure. A unit advertised as 14,000 BTU might only have 8,000 BTU SACC.
Check the SACC rating or the new “DOE BTU” rating for realistic expectations.
Energy Efficiency: EER and CEER
EER (Energy Efficiency Ratio) = BTU output ÷ watts consumed. Higher is better.
Window ACs:
- Below 9.0: Inefficient
- 9.0-10.5: Average
- 10.5-12.0: Good
- 12.0+: Excellent
Portable ACs:
- Below 8.0: Inefficient
- 8.0-9.0: Average
- 9.0-10.0: Good
- 10.0+: Rare but excellent
CEER (Combined Energy Efficiency Ratio) accounts for off-mode and standby energy use—a more comprehensive efficiency measure now required on newer models.
A unit with EER 10.0 running 8 hours daily costs roughly $40-60/month at $0.12/kWh. EER 12.0 costs $32-50/month for the same cooling. Over a summer, efficiency differences add up.
Noise: The Forgotten Factor
Air conditioners are loud. Some are tolerable. Others are conversation-stopping.
40-45 dB: Quietest units, acceptable for bedrooms
45-52 dB: Most window and portable ACs fall here, noticeable but tolerable
52-60 dB: Loud, difficult to sleep through, conversation over it is challenging
60+ dB: Very loud, acceptable only if you’re desperate
Window units are typically 50-56 dB. Portable ACs often hit 52-60 dB because all components are in the room with you.
If bedroom cooling is your priority, noise matters as much as cooling capacity. Sleep-deprived summers are miserable.
Installation Reality Check
Window Units:
Need proper window size (measure your window opening first). Most fit double-hung windows 23-36 inches wide. Require support bracket for safe installation. Weatherstripping the gaps is crucial for efficiency. Installation takes 30-60 minutes for first-timers.
Portable ACs:
Included window kit usually fits standard windows. You’re essentially shoving an exhaust hose through a partially open window and sealing around it. Takes 10-15 minutes. Won’t work well with casement or sliding windows without modifications.
Through-the-Wall:
Requires a wall sleeve (often sold separately). Need to cut a hole in your exterior wall or use an existing sleeve. This is DIY-possible but intimidating. Many people hire professionals.
Mini-Splits:
Professional installation required unless you’re HVAC-savvy. Mounting indoor unit, drilling wall hole, running refrigerant lines, connecting to outdoor unit, evacuating air from lines, charging system. Not a DIY project for most people.
Smart Features and Modern Conveniences
Wi-Fi/App Control:
Turn AC on before arriving home, monitor energy use, set schedules. Useful but not essential. Worth paying $30-50 extra, not $200 extra.
Voice Control:
Alexa/Google Home integration. Convenient if you’re already invested in smart home ecosystems.
Sleep Mode:
Gradually adjusts temperature overnight for comfort and energy savings. Actually useful, especially in bedrooms.
Eco Mode:
Adjusts compressor speed for energy efficiency. Can sacrifice cooling speed for lower energy use.
Programmable Timer:
Set on/off times. Helpful for managing energy costs by cooling only when home.
Auto-Restart:
Remembers settings after power outages. Valuable if you’re away and power cuts out.
Washable Filters:
Saves money on replacement filters. Clean monthly during heavy use.
Common Mistakes That Waste Money
Buying based on room size charts alone. Factor in sun exposure, ceiling height, and heat sources. Those charts assume ideal conditions.
Ignoring air sealing. Gaps around window units or portable AC hoses waste massive cooling. Seal them properly.
Running AC at 60°F to cool faster. It doesn’t cool faster—it just runs longer and uses more energy. Set it to your target temp (usually 72-76°F).
Placing portable ACs near heat sources. Away from direct sunlight, away from appliances, away from electronics generating heat.
Never cleaning filters. Dirty filters reduce efficiency by 5-15%. Clean or replace monthly during cooling season.
Oversizing significantly. More BTU isn’t better if it’s way more than you need. Short cycling (constantly on-off) reduces dehumidification and efficiency.
Forgetting about humidity. AC should remove humidity as it cools. If your room feels cool but clammy, the AC is short-cycling (oversized) or not running long enough.
When Window ACs Beat Portables
Window units are almost always more efficient and effective. Choose a window unit if:
- You have compatible windows
- You can physically install it (or have help)
- You’re okay with it staying for the season
- Efficiency and cooling power matter most
- Noise is a concern (they’re generally quieter)
- You want the best cooling per dollar spent
When Portable ACs Make Sense
Portables are convenient despite their inefficiency. Choose portable if:
- You rent and can’t install window units
- You need to cool different rooms at different times
- You have incompatible window types
- You need to store it easily off-season
- You move frequently and want to take it with you
- No one can help you install a heavy window unit
What We Evaluate in Reviews
Actual cooling capacity. Does it cool the advertised square footage in real conditions? How long does it take?
Energy consumption reality. Compare stated EER/CEER against actual electricity bills if reported by users.
Noise levels at different settings. Manufacturer specs list minimum noise. What about normal operation?
Build quality and longevity. Does it survive one season or five? Compressor reliability? Control durability?
Installation ease. Are instructions clear? Do included mounting hardware and window kits actually work?
Dehumidification effectiveness. Does it remove humidity properly, or leave rooms feeling clammy?
Customer service quality. Warranty response, defect handling, availability of replacement parts.
Making Your Decision
Measure your room accurately. Calculate square footage, note ceiling height, identify sun exposure and heat sources.
Determine what you can install. Window unit possible? Great, start there. Portable only option? Accept the efficiency trade-off.
Calculate your BTU needs using the adjusted factors, not just basic square footage.
Set a budget that includes energy costs. A $200 efficient unit might cost less over a summer than a $150 inefficient unit.
Consider noise if it’s for sleeping spaces. Check decibel ratings and user reviews about sound.
Then check our detailed reviews. We compare actual performance against claims, highlight reliability issues, and identify which models truly deliver value.
Staying cool shouldn’t be complicated. It just requires the right information and the right tool for your space.