What Size Portable Air Conditioner Do You Need? BTU Explained

The UK weather is a fickle old thing. One moment it's grey and miserable, the next week the sun's cracking the flags and we're all sweating buckets. As summers continue to get hotter, people are looking for ways to keep their houses cool. While fans can help, when temperatures start to hit the high 20s and low 30s outdoors, you likely need an air conditioning unit to keep yourself comfortable when you're out of the sun. It's not as straightforward as just hiring any old portable air conditioner, though. You'll need to make sure you choose the right size air conditioner (measured in BTU), otherwise you run the risk of not getting the desired performance or racking up a high energy bill.

This is because most people make the common mistake of either selecting an air conditioning unit that's too small for their space, reducing how impactful the unit is, or going too big and facing higher running costs than they need and inconsistent temperatures throughout the day as the unit constantly cycles on and off. If you're unsure, hiring an air conditioner can help you avoid an expensive purchasing mistake while ensuring you get equipment that's suited to your exact requirements.

For expert guidance, explore our range of portable air conditioning and cooling solutions or speak to the Speedy team for advice.

 

Why Air Conditioner Size Matters

The "size" of an air conditioner doesn't refer to the physical size of the unit. It instead relates to its cooling capacity, which is measured in British Thermal Units (BTUs), or kilowatts (kW). Not sure what BTU means? Check out our full BTU air conditioning explainer.

The bigger the room or space you're wanting to cool, the larger cooling capacity you'll need from your air conditioning unit. As noted in our Portable Air Conditioner Buying Guide, room volume is one of the most important factors when determining the right cooling solution. Larger rooms and open-place spaces generally require higher BTU ratings to maintain comfortable temperatures.

Choosing the correct size helps you:

• Cool the space efficiently
• Reduce energy consumption
• Maintain consistent temperatures
• Extend equipment lifespan
• Avoid unnecessary hire or purchase costs

BTU vs kW, Explained

Air conditioners are rated according to their cooling capacity, which is typically expressed in either BTU or kilowatts (kW). As noted above, these indicate how much heat they can remove from a space. The higher either number, the better their cooling capacity (but also they'll cost to run). 

While BTU ratings are more commonly used in consumer guides, commercial and hire equipment will sometimes use kW. Both measurements describe the same thing and can be converted easily. You can use the table below to get an 'equivalent' measure.

BTU	Approx kW
5,000	1.5 kW
7,000	2.1 kW
9,000	2.6 kW
12,000	3.5 kW
16,000	4.7 kW
18,000	5.3 kW
24,000	7.1kW

Calculating the Right Air Conditioning Unit Size

To calculate the correct air conditioning unit size, start by measuring the square footage of your room. This is done with the following formula:

Room Area = Length x Width

As an example, let's use my rough living room dimensions which is 16ft by 12ft. Multiplying the two together gives the room a square footage of 192 sq ft. 

Once you have the square footage, you multiple this by 25 BTU. Using my living room example above, this would be:

192 sq. ft x 25 = 4,800 BTU

This calculation gives you a basic indication of the required cooling capacity. However, you also need to consider other factors such as:

• Number of people in the room
• Electrical equipment
• Large windows
• Direct sunlight exposure
• Lighting

These are all additional heat sources that can increase cooling requirements. For example, for every person over two that regularly occupies the room, our product experts recommend adding 600 BTU. On the other hand, if your room is well-shaded during the daytime, you can reduce your calculated BTU by 10%. If your room is in the sun for most of the day, then you'll need to add 10% to your calculated BTU.

• Speedy's air conditioning size and cooling calculator takes all of these into consideration to point you towards the perfect air conditioning unit for your needs.

It's worth noting that air conditioners are manufactured in standard capacity brackets. If your final calculated BTU is around 4,800 as in the example above, you should round up to the nearest widely available size, which is typically a 5,000 or 6,000 BTU unit.

Under-sizing a unit will cause it to run continuously, while slightly over-sizing it ensures efficient cooling. This is especially important for portable air conditioning units, as the compressor and hose to extract it can give off a lot of heat. 

Air Conditioner Size Guide by Room Size

While every environment is slightly different, the room size provides a useful starting point when choosing the right air conditioner size. However, to give you a general idea of the air conditioner size you need for different types of rooms, we've given a general overview below.

2.6kW (9,000 BTU)

• Small home offices
• Living rooms
• Small to medium-sized bedrooms
• Spaces up to 25m² depending on heat load

3.5kW (12,000 BTU)

• Medium-sized living rooms
• Master bedrooms
• Standard-sized home offices with multiple computers
• Spaces up to 35m²

5kW (18,000 BTU

• Larger living rooms
• Open-plan kitchen and dining areas (extra capacity accounts for appliance heat)
• Small, low-traffic retail units or commercial offices
• Areas up to approximately 40m² to 50m²

7.1kW (24,000 BTU)

• Large offices
• Server rooms
• Large retail units
• Areas up to approximately 60m²

Should You Buy or Hire an Air Conditioner?

For both businesses and homeowners, hiring an air conditioning unit typically works out better than purchasing and installing a full air conditioning system in your property or building.

Hiring allows you to:

• Test different sized air conditioning units for different rooms in your space
• Avoid large upfront costs
• Eliminate storage requirements during cooler months (of which there are many in the UK!)
• Scale up cooling capacity during heatwaves
• Make use of flexible hire durations to match your needs as the weather changes

Portable air conditioning hire is particularly useful, as during the UK summer heatwaves you can easily move the unit around your home. Place it in your bedroom overnight to keep you cool during those stuffy nights, move it into your office when working from home, and into the living room or dining room when hosting friends and family over a weekend.

Choosing the Right Air Conditioner with Speedy

Calculating the required BTU can be straightforward for some rooms, but for others, it can devolve into a mess of numbers. Take the stress out of portable air conditioning hire with Speedy. Our product experts at our nationwide depots and on the phones can help make sure you get a unit that's perfect for your space so you stay cool during the scorching summer heat.

With flexible hire durations, competitive rates, and four-hour delivery on selected products, we make it easy for you to get the air conditioning your house or workplace needs to stay comfortable.