Buying the wrong size portable air conditioner is an easy mistake to make. Underpowered models will leave you sweating all summer long. Units that are too powerful will leave you throwing away money on your utility bills.
Take the time to size your portable AC correctly from the beginning and you’ll save yourself money, time, and headaches.
Need help figuring out how to do it? Don’t sweat it. We’re here to show you step-by-step how to select the right portable air conditioner for your space. By the time you’re done reading, you’ll feel 100% confident at choosing the perfect unit every time.
What Is a BTU?
Before we get started you should understand one very important term. BTU refers to British Thermal Units. BTUs measure how much heat your AC will be able to remove from your room every hour.
The higher the BTU rating, the more cooling power the portable AC has. Room dimensions are the key factor in calculating BTU needs. A small bedroom will require much less cooling power than a large, open living room.
How to Select the Right Portable Air Conditioner Size
Selecting the proper BTU rating for the space you wish to cool is the single most important step when purchasing a portable air conditioner. Choose a unit with too few BTUs and it will run constantly without ever getting your room cool enough. Choose one with too many BTUs and it will cycle on and off too quickly. This can cause the room to feel clammy and humid.
Step 1: Know the square footage of the area you want to cool.
Grab your tape measure and find the length and width of the room you wish to cool. Multiply those two figures together to calculate square footage.
Let’s say you have a room that is 15 feet long and 20 feet wide. It has 300 square feet of space (15 x 20 = 300). That is the number you will use to help select the proper BTU rating for your portable AC.
If you intend to cool multiple rooms that are connected to each other (open floor plan) simply add together their square footage.
Step 2: Select the right BTU range.
Now that you know how big your room is, you can easily refer to the following helpful guide to match your square footage to BTUs.
- 100 – 150 sq ft = 5,000 BTUs
- 150 – 250 sq ft = 6,000 – 7,000 BTUs
- 250 – 350 sq ft = 8,000 – 10,000 BTUs
- 350 – 450 sq ft = 10,000 – 12,000 BTUs
- 450 – 550 sq ft = 12,000 – 14,000 BTUs
- 550 – 700 sq ft = 14,000 – 16,000 BTUs
These figures should be your baseline. However, there are other circumstances that may require you to increase or decrease your BTU needs slightly.
Step 3: Make adjustments for your room’s conditions.
Every room is different. Various unique conditions can impact how hard your portable AC will need to work.
Does your room get direct sunlight? If so, it will heat up quicker than you think. Add an additional 10% to your BTU estimate if your room receives direct sun, especially if it faces south or west.
- Ceiling height – Rooms with ceilings higher than 10 feet require more cooling power. Take into account the extra square footage of air that larger ceilings create.
- Number of people normally in the room – Each additional person adds body heat to the room. Add 600 BTUs for each person if more than two people will be regularly using the room.
- Kitchen – Cooking areas are hot! Kitchens and rooms frequently used for cooking should have their BTU needs increased by around 4000 BTUs. Rooms adjoining the kitchen should also be increased because heat from cooking appliances will spread to those areas as well.
Does your room have single-paned windows? Does your home have poor insulation? These factors can also reduce your room’s efficiency. Rooms that aren’t well insulated will require additional BTUs.
Is Bigger Better?
Many folks assume that bigger is always better. Don’t fall into that trap with air conditioners. Too big of a unit will cause something known as short cycling.
Short cycling means the unit quickly turns itself off after reaching the temperature you set. This problem can cause your room to feel sticky or clammy. Air conditioners also remove moisture from the air as they run. Short cycling prevents the unit from adequately dehumidifying the room.
Too much humidity can lead to mold growth as well. Always try to stay as close to your BTU needs as possible.
What else should I look for?
BTUs and hose type are important but here are a couple other things you should look at before making your purchase.
- Energy efficient ratio (EER) – The higher the EER rating the less electricity your unit will use to create cooling power. A decent portable AC should have an EER of at least 10.
- Noise level – Some portable AC units can be loud. If you’ll be using it in a bedroom or other space where noise is an issue, pay attention to the decibel rating before you buy.
- Auto-evaporation drain pump or manual drain – Some units come with auto-evaporation features. These remove moisture from the air without needing a bucket to catch condensation. Others do require a bucket and must be drained manually.
- Weight – Most portable ACs range from about 50lbs to 80lbs. Make sure the unit has durable casters to help you move it around if needed.
Which Type Should I Buy? Single-Hose vs. Dual-Hose Units
Now that you know the square footage of the room you want to cool you should also understand the difference between single-hose and dual-hose portable air conditioners.
A single hose unit takes the air from inside your room and forces it through the air conditioner. Then the hot air is exhausted outside through the hose. When using a single hose portable AC, be aware that it pulls air from the rest of your home to make up for air that’s being sucked out. Basically, it creates negative air pressure which in turn draws warm air in from other rooms.
Dual-hose models don’t have this problem. They bring in outside air through one hose and exhaust hot air through a second hose. Dual hose units are much better at cooling large rooms and are more efficient. Dual-hose portable ACs are recommended for rooms larger than 400 sq ft in hotter climates.
Real Example UK: Cooler Costs Cutting in a London Flat
Flat details: 1-bedroom apartment located in London. Cool mainly suffers from heat gain in the afternoon when the sun shines directly into the living room space. The occupant previously used a 10,000 BTU portable air conditioner to cool their flat for around 6–8 hours each day.
Problem:
- Electricity bills were 35% higher in the summer months
- Unit had trouble keeping cool during peak heat times
- Air inside felt stuffy/dry
Solution:
The air conditioner was switched out for a mid-sized evaporative air cooler. User made some minor behavioral changes:
- Left windows cracked open during the day
- Closed blinds when the sun was strongest
- Used mainly during the hottest parts of the day
Results (after 6 weeks):
- Cooling energy consumption decreased by ~60%
- Electricity bills were roughly £40–£60 cheaper per month
- Room air smelled and felt fresher from the ventilation
Worked well during dryer periods of the summer (didn’t cool well during humid week)
Moral of the story: Air coolers can be a great option to cut energy costs for cooling smaller properties over the summer in the UK. ( flats/london homes where you don’t necessarily need to have your entire home covered by an AC unit.) Do keep in mind that their performance will be affected by humidity, which can vary greatly in the UK.
Link: https://airability.co.uk/case-studies/evap-cooling-cs/
UK Air Cooler FAQs
1. How much electricity does an air cooler use?
Air coolers typically use between 100W-300W. This translates to only a few pounds per month in the UK, depending on your tariff and how often you use it.
2. Are air coolers cheaper than air conditioners?
Yes. You can save between 70-90% on electricity compared to running a traditional air conditioning unit.
3. Will an air cooler work in the UK?
Air coolers are great for those hotter, dryer days we get in the UK. However, they will lose cooling efficiency during periods of high humidity (which we do tend to get in the UK.)
4. Can I replace my air conditioner with an air cooler?
Air coolers are best suited for personal cooling, or spot cooling. If you want to effectively cool down a whole room at a time, air conditioners will still outperform air coolers in hotter/humid environments.
5. Do I need to get my air cooler installed?
Nope. Simply fill up the internal water tank and plug it in!
6. How often should I maintain my air cooler?
You should ideally clean your cooler every week (empty out the tank and refill it with fresh water.) Cooling pads will last around 1-2 years depending on usage.
7. Are air coolers bad for the environment?
Not at all. Air coolers don’t use any harmful gases to provide you with cool air, and use drastically less electricity.
