Portable vs Split vs Monobloc Air Conditioners | compare.ac
System types
Monobloc, split or multi-split?
The single biggest decision when buying air conditioning is the system type. It sets your noise, how efficient it is, your space, and whether you can install it at all. Here is each one in plain language.
Type
Install
Outdoor unit
Noise
Efficiency
Typical cost
Still deciding between two types?
Head-to-head on price, noise, efficiency and install, from the real in-stock units we track, with the best current pick of each type.
A single self-contained box on castors that you wheel into any room and vent through a window with a flexible hose.
Everything (compressor, condenser, evaporator) sits in one cabinet, so the whole refrigeration cycle happens inside the unit. It draws warm room air across the cold coil and pushes the collected heat out of the building through one or two flexible exhaust hoses fed through a window-seal kit. Single-hose models exhaust room air outdoors and pull replacement air in through gaps, while dual-hose models take outdoor air for condenser cooling separately.
Genuinely DIY and tool-free: unbox, attach the supplied hose and window-seal panel, plug into a normal socket, done in 10-15 minutes. No drilling, no wall penetration and no refrigerant work, because the sealed circuit is factory-charged and never opened. Condensate is either auto-evaporated out of the hose or collected in an internal tray you empty (some models take a gravity drain hose).
Regulation impact
How much cooling you need
Sizing in one rule of thumb
compare.ac sizes every room against the official ENERGY STAR room air conditioner chart, a genuine bracket table rather than a flat rate per square foot: about 5,000 BTU (1.5 kW) for a small room up to 150 sq ft (14 m2), rising to about 12,000 BTU (3.5 kW) around 500 sq ft (46 m2) and 18,000 BTU (5.3 kW) around 1,000 sq ft (93 m2). This figure assumes a temperate summer: a hot or humid region realistically needs roughly 20 to 30 percent more, and a mild, maritime climate a little less, which the tool applies once you pick your region. Add about 10% for strong afternoon sun, about 4,000 BTU for a kitchen, and about 600 BTU for each person regularly in the room beyond two; a ceiling above the standard height scales the load further by volume, not floor area.
Room
Area
Cooling (BTU)
kW
Small bedroom or home office
129 sq ft(12 m²)
5,000
1.5 kW
Standard double bedroom
194 sq ft(18 m²)
6,000
1.8 kW
Living room
269 sq ft(25 m²)
The jargon, decoded
Glossary
BTU (British Thermal Unit per hour)
An imperial measure of cooling power, written BTU or BTU/h. Larger numbers cool more. Roughly 3,412 BTU equals 1 kW. Listings often quote BTU; compare.ac shows kW alongside so you can compare.
kW (kilowatt of cooling)
The metric measure of how much heat the unit removes per hour, used alongside BTU (1 kW is about 3,412 BTU). US listings lead with BTU; compare.ac shows both. As a reference point, a typical 270 sq ft living room needs around 7,000 BTU, or about 2.1 kW, on the ENERGY STAR chart.
SEER (Seasonal Energy Efficiency Ratio)
How efficiently a unit cools across a whole season, not just at one moment. Higher is better. US mini-splits are rated on SEER2, the current Department of Energy test that replaced SEER. Window and portable units use CEER instead, which is a different scale: a SEER2 number and a CEER number cannot be compared directly.
SCOP (Seasonal Coefficient of Performance)
The heating-mode equivalent of SEER, for reverse-cycle units that also heat. Higher is better. It is a European measure; the US equivalent on heat pumps is HSPF2, and most US room-AC listings publish neither.
EER (Energy Efficiency Ratio)
Efficiency at a single fixed operating point, usually peak heat. It is the older, simpler measure that SEER replaced for everyday comparison. Useful for portables, which are often rated by EER (good inverter splits reach 3.5 to 5.0; portables are typically 2.0 to 2.5).
Common questions
Frequently asked
Is this a real air conditioner or just a fan or air cooler?
A real air conditioner has a refrigerant compressor and can lower a closed room below the outdoor temperature, and it is rated in kW or BTU of cooling power. A fan only moves air and removes no heat. An evaporative 'air cooler' blows air over water, adds humidity, needs a window open, and cannot reach a set temperature. compare.ac lists only units with a genuine refrigeration cycle, so everything you see here is a real AC.
What is the difference between a monobloc, a single split, and a multi-split?
A portable monobloc keeps the whole machine in one box in the room and vents hot air through a hose to a window. It needs no installation but is louder (typically 52 to 58 dB(A)) and less efficient. A single split has a quiet indoor unit and a separate outdoor unit connected by pipes, so it is much quieter (indoor unit often around 19 to 35 dB(A)) and far more efficient, but it must be professionally installed. A multi-split is one outdoor unit feeding several indoor units, which is the right choice when you want to cool two or more rooms without a separate outdoor box for each.
Do I need permission or a permit to install one?
For a portable monobloc or most window units, no: you can use them yourself with no permit. For a split or multi-split, often yes. The outdoor unit and the wall penetration are a structural change, so a homeowners' or condo association usually has to approve it, and many US municipalities require a local mechanical or electrical permit for the outdoor unit and its dedicated circuit. Check with your building and your city or county before you buy hardware you may not be allowed to mount.
Do I need a professional installer?
For a split or multi-split, yes. There is no US law banning DIY installation as such, but under EPA Section 608 only a certified technician may open the refrigerant circuit, and the EPA states plainly that this includes connecting or disconnecting the pre-charged line sets sold with “DIY” mini-split kits. That is worth knowing, because it is the opposite of how those kits are usually marketed. Doing the refrigerant work yourself voids the manufacturer warranty and risks a dangerous, illegal release. A portable monobloc, and most window units, need no installer at all: they are factory-sealed, so you set the unit down or fit it in the window and run the exhaust yourself.
How much cooling power do I need for my room?
A common US rule of thumb for a standard, reasonably insulated room with an 8-foot ceiling is about 20 BTU per hour per square foot, so a 300 sq ft room is often quoted around 6,000 BTU and a 500 sq ft room around 10,000 BTU. compare.ac instead sizes against the official ENERGY STAR room air conditioner chart, which is not a flat rate: it recommends about 7,000 BTU for that same 300 sq ft room and about 12,000 BTU for a 500 sq ft room, then adjusts up for a hot or humid climate and down for a mild one once you pick your region. Add capacity for a sunny west-facing or top-floor room, a kitchen, or extra people who are regularly in it. Undersizing means the unit runs flat out and never cools; oversizing short-cycles and leaves the room cool but clammy.
How much noise is acceptable?
Noise is measured in dB(A). A quiet split indoor unit on a low setting can be around 19 to 25 dB(A), which is barely audible and fine for a bedroom. Around 30 to 35 dB(A) is a soft hum that most people accept in a living room. Portable monobloc units are usually 52 to 58 dB(A) because the compressor sits in the room with you, which is closer to a dishwasher and can disturb sleep. If quiet matters, a split almost always wins; if you only cool occasionally, a portable may be acceptable.
What will it cost to run, and what do the efficiency ratings mean?
Running cost is driven by efficiency: CEER on window and portable units, and SEER2 on mini-splits. Higher is better on both, but they are separate scales and a SEER2 number cannot be read as a ratio against a CEER number. Directionally, an efficient inverter mini-split is the cheapest type to run, while a single-hose portable can cost roughly two to three times as much for the same comfort, because much of its capacity is lost back through the exhaust hose. For window and portable units that ENERGY STAR certifies, we go a step further and show an estimated dollars-per-year figure, taken from the model's published annual energy use (a DOE test that assumes about 750 hours of cooling a year) priced at the average US residential electricity rate. It is a standardized figure for comparing units, not a personal bill: your real cost depends on how much you run it, your local electricity rate, and your climate. Mini-splits are usually the most efficient of all but are rated on SEER2, so we do not convert those to a dollar figure, and a missing running cost is a data gap, never a sign a unit is worse.
Can renters install air conditioning?
Yes, but the practical answer depends on the type. A portable monobloc needs no installation and no permission, so it is the realistic option for most renters: you only need a window to run the hose. A window unit is usually fine too, though your lease may set conditions and a support bracket is often required. A split or multi-split drills through the wall and adds an outdoor unit, so it requires written landlord permission, an EPA Section 608 certified technician to handle the refrigerant, and often an agreement about whether it stays or is removed when you leave. For short tenancies, a portable or a window unit is usually the sensible choice.
What refrigerant should the unit use, and does R-32 matter?
Most current home AC uses R-32 (GWP 675) or R-454B (GWP 466), both far lower in global warming potential than the R-410A (GWP 2,088) they replaced. Under the AIM Act, the EPA has prohibited manufacturing or importing residential AC and heat pumps that use refrigerant at or above 700 GWP since January 1, 2025, which is why new equipment ships with R-32 or R-454B. Equipment built or imported before that date may still legally be installed: the EPA removed the install-by deadline it had originally set, so remaining R-410A stock is not stranded. Either way, an R-32 or R-454B unit bought today is on the right side of the transition. compare.ac lists the refrigerant for every unit.
Why does a portable air conditioner sometimes feel weak?
A single-hose portable pushes its hot exhaust out of one tube. That creates negative pressure indoors, which sucks warm air back in through gaps around doors and windows, so in real conditions it often delivers only about half to two-thirds of its rated capacity. It is still a real AC and will cool a room, just less than the box claims. Sizing up, sealing the window kit well, or choosing a split where possible all help.
Does my climate change how much cooling I need?
Yes, more than almost anything except the size of the room. compare.ac's base sizing, before any climate adjustment, follows the official ENERGY STAR room air conditioner chart, which assumes a temperate summer. A hot, dry region like Arizona, or a hot, humid one like Florida and the Texas Gulf coast, realistically needs on the order of 20 to 30 percent more cooling per square foot, because the outdoor design temperature is higher and, in humid places, the unit also spends energy removing moisture (the latent load). A mild, marine climate such as the Pacific Northwest or coastal New England needs a little less. compare.ac applies this adjustment once you pick your region in the tool, using ASHRAE Standard 169 design temperatures and ACCA Manual-J regional sizing practice, and always shows both your real room size and the adjusted figure it sizes against. For a final purchase, a professional Manual-J load calculation for your specific home is the accurate method.
The most regulation-light option by far. No EPA Section 608 certified technician is needed because the refrigerant circuit is factory-sealed and never opened, no building or mechanical permit is triggered since nothing is fixed to the structure, and a landlord has little ground to refuse a unit that leaves no permanent alteration. The real constraints are your lease or HOA rules on how the window kit looks from outside, and noise to neighbours.
Noise
The loudest type for the occupant because the compressor sits in the room with you, typically 50-60 dB(A) sound pressure (a quiet model around 54 dB(A), noisier ones up to 65 dB(A) sound power). Dual-hose units tend to be slightly louder due to a second fan. Often too loud for light sleepers in a bedroom.
Efficiency & running cost
The least efficient category. US portables are rated on SACC (Seasonally Adjusted Cooling Capacity), the Department of Energy test figure, which lands well below the raw ASHRAE BTU number a box often advertises because it accounts for the heat that leaks back in through the exhaust hose. Single-hose designs lose more real-world performance still, because the slight negative pressure they create pulls hot outside air back in through door and window gaps. Dual-hose models avoid that and cool noticeably faster for the same rated capacity. Note that a portable's SACC and CEER are not comparable to the CEER printed on a window unit.
Space, indoor & out
Takes floor space indoors; zero footprint outdoors. Best where you cannot or will not put anything on the wall or facade.
Typical cost
$250-600 for the unit (budget single-hose around $250-350, better dual-hose and inverter models $450-600). No installation cost because you fit it yourself.
Pros
Truly DIY, no installer, no drilling, no refrigerant handling
No permits, no EPA 608 technician, landlord-friendly
Cheapest entry point and movable between rooms
Zero outdoor unit, so facades, balconies and shared walls stay clear
Cons
Lowest efficiency, so highest running cost per kW of cooling
Loudest option because the compressor is in the room
Single-hose models pull warm air back in and cool unevenly
Bulky on the floor and the window hose blocks part of the window and lets warm air leak
Best for: Renters, landmarked or historic buildings, HOAs that ban anything in the window, and anyone who needs cooling without permission, drilling or a permanent install, plus people who want to move the unit between rooms.
Worst for: Bedrooms where quiet matters, large or multiple rooms, whole-flat cooling, and anyone wanting low running costs over a full summer.
Variants
Single-hose vs dual-hose: single-hose is cheaper and simpler but creates negative room pressure that draws hot air back in, while dual-hose uses a separate intake to cool the condenser and cools larger rooms faster and more efficiently. A small subset are heat-pump (reverse-cycle) models that also warm in winter.
A single box that sits half-inside, half-outside a window opening, dumping heat directly to the street with no hose.
Like the monobloc it is one self-contained box, but instead of a hose it straddles the window: the cold front faces the room and the hot condenser end hangs outside, so heat is rejected directly to the air without a duct. The sash is closed down onto the unit and side panels seal the gaps. The factory-sealed refrigerant circuit never needs to be opened.
DIY-friendly in principle (no refrigerant work, sealed circuit) but physically awkward: the unit is heavy, must be lifted into the opening, levelled with a slight outward tilt for condensate drainage and braced or bracketed so it cannot fall. It fits double-hung and sliding sash windows, the standard US residential window, which is why it is a mainstream category here. Casement and awning windows need a different unit.
Regulation impact
No EPA Section 608 technician is needed: the refrigerant circuit is factory-sealed and never opened. A plug-in window unit needs no permit, so the friction is with your building rather than the government. Many HOAs restrict window units on appearance grounds, though an HOA regulating how you mount one stands on much firmer ground than one banning cooling outright. Landlords can set conditions, and the falling hazard is taken seriously: New York City, for instance, requires window units to be supported by brackets or mounting rails, and many building insurers and HOAs now require a bracket regardless of city.
Noise
Moderate to occupant: the compressor is in the box at the window, so indoor sound pressure is typically 42-58 dB(A) depending on model and fan speed. Quieter than a portable monobloc because half the machine and most of the noise is outside, but the noise is projected outward to neighbours and the street.
Efficiency & running cost
More efficient than a portable monobloc because heat is rejected straight outside with no hose losses and no negative-pressure infiltration. Modern inverter models reach EER around 3.5 and can be ENERGY STAR rated (EER roughly 12-15 in US units), though they still trail a proper split system.
Space, indoor & out
Frees indoor floor space and needs no wall mounting, but permanently occupies one window and protrudes outdoors. Trades a usable window for cooling.
Typical cost
$250-500 for the unit (a basic 8,000 BTU model around $250-300, larger or inverter models $400-500). DIY install is free; an optional bracket or handyman fitting adds little.
Pros
More efficient than a portable monobloc, heat goes straight outside
Frees up floor space and needs no hose or drilling
No refrigerant work, no EPA 608 technician, owner-installable
Lower cost than any split system
Cons
Only fits double-hung or sliding sash windows, not casement or awning
Blocks the window and is visible from outside, which many HOAs restrict
Heavy and a falling hazard on upper floors, needs secure bracketing
Best for: US-style sliding or double-hung windows, single rooms, budget-conscious owners who want better efficiency than a portable without a pro install.
Worst for: Casement and awning windows, HOAs that prohibit window units, anyone who needs the window to open normally, and upper-floor apartments without a properly rated support bracket.
One slim indoor wall unit linked by pipes to one quiet outdoor compressor, the efficient mainstream choice for cooling a single room well.
The system is split into two boxes: a quiet indoor evaporator (usually wall-mounted) and an outdoor unit holding the compressor and condenser, joined by insulated copper refrigerant pipes plus a power and condensate line through a small wall hole. Keeping the noisy, hot components outside lets the indoor unit run very quietly and the inverter compressor modulate output for high efficiency. Almost all are reverse-cycle heat pumps, so they also heat in winter.
Professional install required, not DIY. It involves drilling a core hole through the wall, mounting both units, running and pressure-testing the pipework, pulling a vacuum and releasing the factory charge. Even pre-charged quick-connect kits still legally require a certified engineer to make and pressure-test the final refrigerant connection. Half-day to a full day of work.
Regulation impact
This is where regulation bites. Under EPA Section 608 the refrigerant circuit may only be opened by a certified technician, and the EPA is explicit that this includes connecting or disconnecting the pre-charged line sets sold with "DIY" mini-split kits. No federal law stops you doing the mounting, bracketing and line routing yourself, but handling the refrigerant without certification voids the warranty and is a violation. Most US jurisdictions also require permits for a new outdoor unit: typically mechanical or building for the wall penetration and mount, plus electrical for the dedicated 240 V circuit and disconnect. An HOA nearly always has to approve exterior equipment in advance, and local noise ordinances can cap how loud the condenser may be at the property line. This varies by city and county, so confirm with your building department before buying hardware.
Noise
The quietest type indoors: wall units run as low as 19-30 dB(A) on low fan, near-silent for a bedroom. The outdoor unit sits at roughly 40-60 dB(A) but it is outside, so the only noise concern is to neighbours, which is why local noise limits and unit placement matter.
Efficiency & running cost
The efficient choice. Inverter compressors and proper outdoor heat rejection give a high SEER2; good units reach the high teens and premium models go well beyond. Lowest running cost per unit of cooling of the four, and the heat-pump mode is efficient for shoulder-season heating too. SEER2 is a seasonal scale and is not comparable to the CEER printed on window and portable units, so do not read a mini-split's bigger number as a direct efficiency ratio against them.
Space, indoor & out
Frees all indoor floor and window space (just a slim wall unit), but commits one spot on the external facade to the condenser. The best indoor footprint of any fixed type.
Typical cost
$2,500-6,000 fully installed for a typical room (the equipment is roughly $700-1,800, professional installation roughly $1,500-4,000+ depending on line-set run, electrical and access). The unit price you see here is hardware only; installation is the larger, separate cost.
Pros
Highest efficiency and lowest running cost of the four
Near-silent indoors, ideal for bedrooms
Reverse-cycle heating included, useful all year
No floor space used and no window blocked
Cons
Refrigerant work requires an EPA 608 certified technician, not DIY
Highest upfront cost once installation is included
Outdoor unit alters the facade and usually needs permission or consent
Permanent install, hard to take with you when you move
Best for: A bedroom, living room or home office you want cooled quietly and cheaply to run, owners (or renters with consent) able to commit to a permanent install, and anyone who also wants winter heating.
Worst for: Renters who cannot get written landlord consent, HOAs that restrict exterior equipment, landmarked properties, anyone needing a same-day no-install solution, and homes with no viable outdoor unit location.
One outdoor unit feeding several indoor units, so a whole flat or house can be cooled room by room with a single condenser on the facade.
It is a split system scaled up: a single larger outdoor condenser connects via separate refrigerant pipe runs to two and up to five or six indoor units, each in its own room. Every indoor unit has its own remote and thermostat so rooms are controlled independently, while just one box sits outside. The same inverter and sealed-refrigerant principles as a single split apply, only with more pipework.
Installation
Professional install, and more involved than a single split: each indoor unit needs its own drilled wall penetration, its own pipe run back to the shared outdoor unit, plus the same vacuum, pressure-test and certified refrigerant connection. Multi-day job, planned around pipe routing through the building.
Regulation impact
The same EPA Section 608 certified-technician requirement as a single split, applied across a bigger system. Because it touches multiple rooms and routes line sets through the structure, it more often triggers a full permit set (mechanical, electrical and sometimes building), HOA architectural approval, and written landlord consent. Local noise limits at the property line apply to the outdoor unit just as for a single split, though one shared condenser is usually easier to get approved than several separate ones.
Noise
Per room it matches a single split: very quiet indoor units around 19-30 dB(A). The one outdoor unit is larger and a little louder (around 45-60 dB(A)) and runs whenever any zone calls for cooling, so its placement relative to neighbours matters more.
Efficiency & running cost
High inverter efficiency like a single split, rated on the same SEER2 scale, and it avoids the cost and clutter of several outdoor units. Slightly less efficient than the same number of separate single splits in some part-load conditions, but far more efficient and cheaper to run than cooling each room with portables.
Space, indoor & out
Best whole-home balance: slim indoor units use no floor space and only one spot on the facade is taken regardless of how many rooms are cooled.
Typical cost
$5,000-15,000 fully installed depending on the number of zones (roughly $3,000-8,000+ for the multi-zone install on top of the equipment). A 2-room (2x1) setup sits near the lower end, a 4-5 room whole-home system near the top. The unit price you see here is hardware only; installation is the larger, separate cost.
Pros
Cools the whole home with just one outdoor unit on the facade
Independent temperature control in every room
High inverter efficiency and reverse-cycle heating in every zone
Mixes indoor unit styles (wall, floor, ceiling, ducted) to suit each room
Cons
Highest upfront cost of the residential options
Most complex install, EPA 608 certified technician and multiple line runs
If the single outdoor unit fails, every room loses cooling
Best for: Cooling a whole flat or house room by room, owners doing it properly with year-round heating, and anyone who wants only one outdoor unit on the facade instead of several.
Worst for: A single room (a single split is cheaper and simpler), tight budgets, renters without firm written consent, and buildings where an HOA or a landmark designation restricts any external unit.
Variants
For larger or higher-end homes the same one-outdoor-many-indoor idea extends to professional configurations. Ducted/central systems hide a concealed indoor unit in the ceiling or loft and distribute air through ductwork to grilles for an invisible, whole-house finish. Ceiling cassettes recess flush into a suspended ceiling and blow air in two or four directions. Floor consoles sit low on the wall like a radiator for rooms where wall-high or ceiling mounting is impractical. At the top end, multi-zone VRF/VRV systems (variable refrigerant flow) scale this further with many indoor units of mixed types on one refrigerant loop, common in large houses and light commercial buildings.
7,000
2.1 kW
Large open living and kitchen (sized up for the kitchen)
431 sq ft(40 m²)
14,000
4.1 kW
South-facing studio with large windows (sized up for sun and glazing)
377 sq ft(35 m²)
10,000
2.9 kW
Getting the cooling power right matters more than any feature. Too little and the unit runs constantly without ever cooling the room; too much and you pay for capacity that cycles on and off and controls humidity poorly. These figures are a practical starting point for typical, reasonably insulated rooms with a standard ceiling height of about 8 to 9 ft (2.4 to 2.7 m). Always size up for sun-traps, large windows, kitchens, top-floor rooms, or rooms with several people.
dB(A)
Noise level in A-weighted decibels, the scale that matches how human ears hear. Lower is quieter. A quiet split indoor unit can be under 25 dB(A); portable units are commonly 52 to 58 dB(A) because the compressor is in the room.
R32
The refrigerant in most modern home AC. It cools efficiently and has a global warming potential of 675, much lower than the older R410A it replaced. It is flammable in high concentration, which is one reason certified installation is required.
F-gas
Fluorinated greenhouse gases used as refrigerants. In the US they are governed by the AIM Act, under which the EPA runs an HFC phasedown and has barred new residential AC built from January 1, 2025 from using refrigerant at or above 700 GWP. "F-gas" specifically names the parallel EU regime ((EU) 2024/573) and its certified-installer rule; the US equivalent for who may handle refrigerant is EPA Section 608.
Energy class (A to G)
The EU label rating efficiency from A (most efficient) to G (least), shown on European listings. There is no US equivalent letter grade: US efficiency is the CEER or SEER2 number itself, and ENERGY STAR certification is the closest thing to a badge.
Monobloc (portable)
A single self-contained unit that sits in the room and vents hot air outside through a hose to a window. No installation or permission needed, but louder and less efficient than a split. The plug-and-play option for renters.
Split
A two-part system: a quiet indoor unit on the wall and a separate outdoor unit, joined by refrigerant lines through the wall. Much quieter and more efficient than a portable, but the refrigerant work needs an EPA 608 certified technician and the install usually needs a permit and permission.
Multi-split
One outdoor unit connected to several indoor units, so you can cool multiple rooms without a separate outdoor box for each. More efficient use of wall space and facade, with the same installer and permission requirements as a single split.
Inverter
A variable-speed compressor that ramps up and down to hold a steady temperature, instead of switching fully on and off. It is quieter and can cut electricity use by around 30 percent versus a fixed-speed (non-inverter) unit. Nearly all good modern AC is inverter.