[Insights] What Size Portable Air Conditioner Should I Hire? Commercial kW Sizing Guide

Choosing the right portable air conditioner to hire starts with one question:

How many kilowatts of cooling do you actually need?

Room size is a useful starting point, but it is rarely enough on its own.

Two rooms with exactly the same floor area can require very different levels of cooling depending on ceiling height, the number of people inside, computers or machinery, sunlight, insulation, outdoor temperature, ventilation and the temperature you are trying to maintain.

For commercial and industrial temporary cooling, you also need to consider where the heat from the portable air conditioner will go, what power is available, whether you need to cool the whole room or only a particular area, and whether one unit or several units will work better.

This guide explains how to estimate the portable air conditioning capacity you may need and what information to have ready before arranging a hire.

Quick answer: What size portable air conditioner should you hire?

For a relatively small enclosed commercial space with a normal ceiling height and moderate heat load, portable air conditioners in the 3.5 to 5.3 kW range may be suitable depending on the specific room and unit.

For example, within the Aircon Rentals fleet:

• A 3.5 kW portable reverse cycle unit is specified for approximately 13 to 29 m².
• A 4.4 kW portable reverse cycle unit is specified for approximately 10 to 29 m².
• A 5.3 kW portable cooling unit is specified for areas up to approximately 35 m².
• A 6.1 kW portable cooling unit has an application area of up to approximately 50 m² in room-cooling mode.

These figures are useful starting points, but they should not be treated as a universal room-size calculator. Actual cooling requirements depend on the heat entering and being generated within the space, along with the target temperature and operating conditions.

A simple starting guide

If you already know what type of temporary cooling you require, view our full portable air conditioner hire range.

What does kW mean on a portable air conditioner?

When an air conditioner is described as a 3.5 kW, 5 kW or 10 kW unit, the figure normally refers to its cooling capacity.

It does not necessarily mean the unit consumes the same amount of electricity.

For example, Aircon Rentals’ 6.1 kW portable cooling unit provides 6.1 kW of cooling capacity, while its listed electrical power consumption is 2.3 kW.

This distinction matters because you need to answer two separate questions:

1. How much cooling capacity does the space require?
2. Can the site supply the electrical power required by the selected equipment?

A 6.1 kW cooling rating therefore does not mean the air conditioner draws 6.1 kW of electricity.

Why room size alone does not tell you how many kW you need

Many air-conditioning sizing charts match floor area directly to cooling capacity.

They can help establish a rough starting point, but commercial temporary cooling often involves far more variables.

Consider two rooms.

Room A

• 30 m² office
• 2.7 m ceiling
• four people
• four laptops
• limited direct sunlight
• reasonably insulated

Room B

• 30 m² communications room
• 2.7 m ceiling
• several racks of operating electronic equipment
• equipment operating continuously
• cooling required 24 hours per day

Both rooms are 30 m².

But their cooling requirements can be very different because Room B contains a significant and continuous internal heat load.

The square metres are the same. The cooling requirement is not.

A Simple Office Cooling Rule of Thumb

For a standard enclosed commercial office, a useful preliminary office cooling estimate is approximately 120 to 150 watts per square metre.

For example, for a 30 m² office:

30 × 0.12 = 3.6 kW

to:

30 × 0.15 = 4.5 kW

So approximately 3.6 to 4.5 kW of cooling may be a reasonable starting point for a standard 30 m² office.

This is only a preliminary estimate. High occupancy, IT equipment, extensive glazing, direct sunlight, high ceilings, poor insulation and high outdoor temperatures can all increase the required cooling capacity.

Step 1: Measure the room

Start with the basic dimensions:

Length × width = floor area

For example:

6 metres × 5 metres = 30 m²

That gives you a useful starting point.

But also record the ceiling height.

A 30 m² room with a 2.4 m ceiling contains:

72 m³ of space

A 30 m² room with a 4 m ceiling contains:

120 m³ of space

That is around 67% more volume, despite both rooms appearing as 30 m² on a basic room-size chart.

This is why room volume and building characteristics matter.

Ceiling construction can also affect the installation, particularly when hot-air ducting needs to pass through or above the ceiling. If you are unsure what type of ceiling is installed at your site, see our guide to common ceiling types.

Step 2: Decide what you are actually trying to cool

Before selecting an air conditioner, define the objective.

There are three common temporary cooling situations.

Whole-room comfort cooling

You want to control the general temperature of an enclosed area such as:

• an office
• meeting room
• reception area
• retail space
• temporary site office
• staff room
• enclosed workspace

In these situations, room dimensions are an important part of sizing.

Equipment or critical-room cooling

You may need cooling because equipment is producing heat or needs to stay below a particular operating temperature.

Examples include:

• server rooms
• communications rooms
• data equipment
• electrical rooms
• medical equipment
• temporary plant rooms

Here, the heat generated by the equipment can be more important than the room’s square metres.

Spot cooling

Sometimes you do not need to air-condition the entire space.

Trying to cool every cubic metre of a large warehouse, for example, may be unnecessary if the actual requirement is to cool staff working at packing stations, machinery or a particular production zone.

A 4.5 kW mobile spot cooling unit can be positioned closer to the people or equipment that actually need cooling.

Larger portable units can also be used for targeted cooling where cooling the whole area is not practical.

Step 3: Identify the heat being generated inside the room

Every heat source inside the space increases the cooling load.

People

People continuously produce heat.

A quiet office occupied by three people has a different load from the same room being used as a training room by 20 people.

When discussing your requirement, provide both:

• normal occupancy
• maximum expected occupancy

Computers and office equipment

Computers, monitors, printers and other electrical equipment release heat into the surrounding space.

A conventional office may only have a modest equipment load.

A trading floor, control room or IT workspace may be completely different.

Servers and electrical equipment

For server rooms and data environments, equipment heat load should be treated as a major sizing input.

Equipment type can also become important if conventional hot-air exhaust is difficult.

Machinery and process equipment

Manufacturing equipment, motors, commercial appliances and other machinery may introduce substantial heat into a space.

Commercial kitchens are a good example.

During a permanent HVAC repair at a fast-food restaurant in Auburn, cooking equipment was already contributing substantial heat to the kitchen. Aircon Rentals used mobile spot cooling to target the areas where cooling was actually required rather than treating the premises as a simple floor-area calculation.

See the temporary air conditioning for a fast-food restaurant case study for the real installation.

That example demonstrates why room size becomes less useful on its own when significant internal heat sources are present.

Step 4: Look at the heat entering the room

The room itself can introduce significant cooling load.

Direct sunlight

Large windows exposed to direct sun can substantially increase the heat entering a room.

Consider:

• window size
• orientation
• shading
• glazing
• time of day

A west-facing office with strong afternoon sunlight can behave very differently from an otherwise identical internal room.

Insulation

A well-insulated office behaves differently from:

• a temporary site shed
• an uninsulated warehouse
• a room beneath a metal roof
• a structure with extensive glazing

Doors opening frequently

A closed office maintains conditioned air more effectively than a retail entrance, loading area or workshop with doors regularly opening.

Every time warm outside air enters, the air conditioner has additional work to do.

Outdoor temperature

Cooling a commercial space on a mild day is different from maintaining the same indoor temperature during extreme summer conditions.

The equipment itself also needs to operate within the expected ambient temperature range.

For example, the 6.1 kW portable cooling unit has a stated operating range extending to 45°C, while the 5.3 kW portable cooling unit is specified to operate in temperatures up to 43°C.

Step 5: Define the temperature you actually need

“Make the room cooler” and “maintain the room below 22°C” are very different requirements.

Before selecting temporary air conditioning, identify:

Current temperature

For example:

32°C

Required temperature

For example:

24°C

How quickly cooling is needed

Is the requirement:

• immediate?
• within a few hours?
• simply to stop the temperature rising further?

Whether the target must be maintained continuously

For example:

• business hours only
• overnight
• 24 hours per day

Comfort cooling generally gives you more flexibility than critical equipment cooling where a maximum temperature must be maintained continuously.

Step 6: Decide whether you need one air conditioner or several

Knowing that you require approximately 10 kW of cooling does not automatically mean one 10 kW unit is the best solution.

The layout matters.

Multiple smaller units may provide better distribution where:

• the room is long or irregularly shaped
• there are several separate rooms
• different areas have different heat loads
• people or equipment are spread throughout the space
• cooling needs to be positioned closer to specific heat sources

One larger unit may make more sense where:

• the space is open
• there is a suitable location for the equipment
• conditioned air can be distributed effectively
• installation requirements can be accommodated
• adequate electrical supply is available

For critical applications, the design may also need to consider what happens if one unit becomes unavailable.

Example 1: What size portable air conditioner for a 25 to 30 m² office?

Imagine an enclosed 28 m² office with:

• standard ceiling height
• four staff
• four computers
• moderate insulation
• limited direct sunlight
• doors generally closed

A portable air conditioner in approximately the 3.5 to 4.4 kW class may provide a sensible starting point for assessment.

The 3.5 kW portable reverse cycle unit is specified for approximately 13 to 29 m², while the 4.4 kW portable reverse cycle unit is specified for approximately 10 to 29 m².

But imagine that same room had:

• ten people
• significant afternoon sun
• poor insulation
• several high-powered workstations

The required cooling capacity could be higher.

The square metres did not change. The heat load did.

Example 2: What size portable air conditioner for a 35 m² office?

Aircon Rentals’ 5.3 kW portable cooling unit is specified to cool an area up to approximately 35 m² under its stated operating conditions.

That makes 5.3 kW a useful reference point for some spaces around this size.

However, you should still check:

• ceiling height
• occupancy
• equipment
• windows
• insulation
• outside conditions
• exhaust arrangement
• electrical supply

A 35 m² meeting room occupied by 20 people during training can have a very different cooling requirement from a 35 m² office used by three people.

Example 3: What size portable air conditioner for a 50 m² room?

Aircon Rentals’ 6.1 kW portable cooling unit lists an application area of 50 m² in room-cooling mode.

Again, treat that as an equipment-specific guide rather than a universal rule that every 50 m² commercial space requires 6.1 kW.

A high-ceiling workshop or heavily glazed room may need more.

A well-insulated room with a low internal heat load may behave differently.

Example 4: What size portable AC for a server room?

This is where using square metres alone can produce a poor result.

Suppose a server room is only 20 m².

A conventional room-size calculator may suggest a relatively small air conditioner.

But if the room contains several kilowatts of continuously operating IT equipment, that equipment becomes a major part of the cooling load.

A Simple Server Room Cooling Calculation

For server rooms, electrical equipment load is usually a much more useful starting point than floor area.

Most of the electrical power consumed by servers and associated IT equipment ultimately becomes heat inside the room.

As a preliminary calculation:

Cooling requirement ≈ active IT electrical load + other heat gains

For example, if the active IT equipment is drawing approximately 6 kW, the cooling system needs to remove at least that continuous heat load.

Depending on the room conditions, UPS losses, lighting, external heat gain, existing cooling and redundancy requirements, the total temporary cooling requirement may be higher.

A preliminary system in the 7 to 8 kW range may therefore warrant assessment for a room with approximately 6 kW of active IT load.

For a more detailed assessment, see our Temporary Server Room Cooling Hire Guide.

For server rooms, provide information such as:

• IT equipment electrical load
• current temperature
• required maximum temperature
• whether equipment operates 24/7
• whether the room has existing cooling
• whether redundancy is required
• whether there is somewhere to reject hot air

The final point matters.

A conventional portable spot cooler moves heat away from the cooled area. That heat still needs to be rejected somewhere else.

Where conventional exhaust is difficult, a water-cooled split system can provide another option.

This approach has been useful in real Aircon Rentals projects.

In one case, a building air-conditioning failure occurred before an important C-suite meeting. A 4.8 kW water-cooled split system allowed the heat-rejection section to be positioned away from the meeting space, helping provide temporary cooling without placing all equipment within the occupied room.

Read the quiet 4.8 kW temporary air conditioning case study.

Access can create a completely different challenge.

At another site, a small service station had limited options for conventional exhaust ducting. A portable water-cooled split allowed the conditioned section and heat-rejection equipment to be positioned separately.

See the Never Too Small to Cool case study for an example of how site constraints can affect temporary air-conditioning selection.

The lesson is simple: the right equipment is determined by both cooling capacity and how the system can actually be installed.

Example 5: What size portable AC for a warehouse?

Start by asking a different question:

Do you actually need to cool the whole warehouse?

For many large industrial spaces, trying to maintain an air-conditioned temperature throughout the entire building may not be practical with portable units.

You may instead need:

• spot cooling at workstations
• cooling around production equipment
• a cooled temporary zone
• multiple units serving separate areas

Portable spot-cooling equipment can be useful where cooling the entire space is unnecessary or impractical.

For large warehouses, workshops and factories, the key distinction is spot cooling versus whole-space cooling. If the requirement is to cool personnel, a workstation, production equipment or a defined zone, directing cooling at the load can be considerably more practical than attempting to condition the entire building volume. A 4.5 kW mobile spot cooling unit can be positioned close to the people or equipment requiring cooling.

If the requirement is to control temperature throughout a larger enclosed commercial or industrial area, reverse-cycle package unit hire or another larger temporary cooling system may be more appropriate than adding multiple small portable units.

Cooling capacity is only half the decision

You can identify the right number of kilowatts and still select the wrong equipment.

The site must actually be able to accommodate the system.

Where will the hot air go?

An air conditioner does not make heat disappear.

It transfers heat from the conditioned area to another location.

For most air-cooled portable systems, the heat removed from the room needs to be discharged somewhere outside the area being cooled.

Depending on the site, that might be:

• outdoors
• through a suitable window
• into an appropriate ceiling void
• into another suitable heat-rejection area

If ceiling space is being considered for ducting, identifying the ceiling construction can help with installation planning. See our ceiling types guide for examples of common configurations.

If there is nowhere suitable to exhaust hot air, a different type of temporary system may be more appropriate.

Is there enough electrical capacity?

Portable does not always mean “plug any number of units into any power point”.

Different units have different electrical requirements.

Several Aircon Rentals portable units use standard single-phase power, but larger equipment may require higher-capacity or three-phase electrical connections.

If several units are being installed, check:

• available circuits
• circuit capacity
• total electrical load
• extension lead requirements
• distribution requirements

This is especially important for server rooms and other 24/7 applications, where temporary cooling may need to operate continuously without overloading an existing circuit.

Can the unit physically reach the location?

Check:

• doorway width
• lift dimensions
• lift weight limits
• stairs
• corridors
• loading access
• where ducting or hoses will run

This can become particularly important in multi-storey buildings or sites with restricted access.

What happens to condensate?

Cooling air can produce condensate.

Depending on the equipment, condensate may be:

• collected in a tank
• pumped away
• managed through another drainage arrangement

The selected system needs to suit the operating hours and site conditions.

For unattended or 24/7 server-room cooling, a continuous condensate pump or suitable drainage arrangement may be preferable to relying on manual tank emptying.

Air-cooled portable AC, spot cooler, water-cooled split or another temporary system?

Once you know approximately how much cooling you need, the next question is which type of equipment can actually deliver it at your site.

Portable reverse-cycle air conditioner

Portable reverse-cycle units are useful for relatively small enclosed areas such as:

• offices
• meeting rooms
• temporary accommodation
• site facilities
• enclosed commercial rooms

Aircon Rentals has portable reverse-cycle equipment in the 3.5 to 4.4 kW class.

View the full portable air conditioner hire range.

If you are deciding between refrigerated cooling and evaporative cooling for a larger or ventilated space, see our Evaporative Cooler vs Portable Air Conditioner guide.

Mobile spot cooler

A spot cooler is useful where you need concentrated cooling around:

• people
• machinery
• workstations
• IT equipment
• production equipment
• a particular part of a larger space

The 4.5 kW mobile spot cooling unit is one example from the Aircon Rentals fleet.

Water-cooled split system

A water-cooled system can be useful where conventional hot-air exhaust arrangements are difficult.

The 4.5 kW water-cooled split system separates the conditioned-air section from the heat-rejection side of the system, providing another installation option for enclosed or difficult spaces.

Larger temporary air-conditioning system

If the required load, area or airflow exceeds what portable units can practically deliver, consider a larger temporary HVAC system.

For example, reverse-cycle package unit hire may provide a better solution for larger commercial or industrial applications.

Aircon Rentals also provides broader temporary cooling solutions where portable units are not the most practical approach.

What happens if the portable air conditioner is too small?

An undersized temporary air conditioner may:

• run continuously
• struggle to reach the required temperature
• lose ground during hotter periods
• fail to manage high internal heat loads
• leave some areas noticeably warmer than others

This becomes particularly important where cooling is protecting business-critical equipment rather than simply improving occupant comfort.

A server room that remains several degrees too warm may have very different consequences from an office that simply feels uncomfortable.

Is bigger always better?

No. Selecting substantially more capacity than the application requires is not automatically the best solution.

The equipment still needs:

• appropriate positioning
• correct airflow
• sufficient power
• suitable heat rejection
• effective temperature control

It may also be more practical to distribute cooling across several smaller units rather than concentrating all capacity in one location.

Correct sizing is about matching the equipment and installation to the actual load.

What information should you have ready before hiring a portable air conditioner?

If you want a faster and more accurate recommendation, collect as much of the following information as possible before requesting a quote.

Space

• room length
• room width
• ceiling height
• approximate floor area
• floor level
• room layout

Temperature

• current indoor temperature
• required temperature
• expected outdoor temperature
• whether the target must be maintained continuously

Heat load

• number of people
• computers and monitors
• servers or IT equipment
• machinery
• lighting
• other heat-producing equipment

Building conditions

• window area
• direct sunlight
• insulation
• external walls
• doors that regularly open
• existing ventilation

Site requirements

• available power
• number and type of electrical circuits
• access to the room
• window, ceiling or external exhaust options
• space for hoses or ducting
• noise restrictions
• required operating hours
• duration of hire

Photographs can also help identify access, heat-rejection and installation constraints.

Portable Air Conditioner Sizing Checklist

Before you contact a temporary cooling supplier, answer these ten questions:

1. How large is the room?
2. How high is the ceiling?
3. What is the current temperature?
4. What temperature do you need to achieve?
5. How many people normally occupy the space?
6. What equipment produces heat inside the room?
7. Does the room receive significant direct sunlight?
8. How frequently are doors opened?
9. What electrical power is available?
10. Where can the heat from the air conditioner be rejected?

If you cannot answer every question, that is fine.

Even a few measurements, photographs and a description of the problem can make equipment selection easier.

Frequently Asked Questions

What size portable air conditioner do I need for 30 m²?

For some relatively low-load enclosed spaces around 30 m², equipment in approximately the 3.5 to 5.3 kW range may provide an appropriate starting point.

The 3.5 kW portable reverse cycle unit is specified for approximately 13 to 29 m², the 4.4 kW unit for approximately 10 to 29 m², and the 5.3 kW unit for areas up to approximately 35 m².

Actual requirements depend on the heat load and room conditions.

Is a 5 kW portable air conditioner enough for an office?

It can be, depending on the office.

An enclosed office with modest occupancy and equipment may need considerably less cooling than the same-size office containing many people, computers and direct afternoon sunlight.

Use room size as a starting point, then assess the internal and external heat loads.

Can one portable air conditioner cool several rooms?

Usually, one unit works best when it can directly circulate conditioned air through the area being cooled.

Separate rooms, closed doors or complicated layouts can reduce effectiveness.

Multiple units may provide better distribution in these situations.

How do you size portable air conditioning for a server room?

Do not rely only on floor area.

Consider:

• heat produced by IT equipment
• required room temperature
• existing cooling
• operating hours
• redundancy requirements
• available power
• how heat will be rejected from the room

Can a portable air conditioner cool a warehouse?

Portable units can be effective for spot cooling or targeted zones within warehouses.

Cooling an entire large warehouse may require multiple units or a larger temporary air-conditioning solution.

Do portable air conditioners need a window?

Not necessarily.

Air-cooled systems need somewhere to reject heat. Depending on the installation, that could be:

• through a window
• through suitable ceiling space
• outside the building
• into another suitable heat-rejection area

A water-cooled system may provide another option where conventional exhaust arrangements are difficult.

Does a 5 kW air conditioner use 5 kW of electricity?

Not necessarily.

The kW rating normally quoted for an air conditioner refers to its cooling capacity.

Electrical input is a separate specification.

For example, Aircon Rentals’ 6.1 kW portable cooling unit has a listed electrical power consumption of 2.3 kW.

Once you know the approximate capacity and equipment type required, see our Portable Air Conditioner Hire Cost in Australia guide for the main factors that affect hire pricing.

Need Help Working Out What Size Portable Air Conditioner to Hire?

The quickest way to choose temporary cooling is to start with the space dimensions and then account for the actual heat load and site conditions.

Aircon Rentals can assess factors including:

• room size and ceiling height
• people and equipment
• current and required temperatures
• spot cooling versus whole-room cooling
• available electrical power
• access
• hot-air exhaust requirements
• number and type of units required

Not sure which capacity or installation will work at your site?

Explore our portable air conditioner hire range or call 1800 626 996 to discuss your temporary cooling requirement.