How to Make a Portable Air Conditioner Colder

Written by: Paul Cathro

Updated on: December 26, 2022

Woman placing AC filter on unit

Portable air conditioners are life savers when the weather hots up, but they can be temperamental at the best of times. 

The most common complaints are insufficient room cooling and the AC unit blowing lukewarm air. The good news is there’s usually an easy fix. 

An insufficiently cold portable air conditioner could be due to an obstruction or ventilation issue, improper cooling capacity, or direct sunlight penetrating the windows and heating the room (among other things). 

This article explores how to make a portable air conditioner colder, with advice on what to check and what to do for optimal cooling. 

How to Make Your Portable AC Colder

There are some simples fixes to make your AC run more efficiently. Make sure you aren't making any of these mistakes.


8. Specify the Correct Cooling Capacity 

Firstly, how much thought did you put into the cooling capacity of your portable AC? 

Cooling capacity measures an air conditioner's ability to remove heat from a space, measured in BTU. "BTU" stands for British Thermal Units - the higher the BTU, the more powerful the cooling effect.  

An air conditioner that is too small cannot cool a room sufficiently. You need around 20 BTUs per square foot of space – for example, if you want to cool 400 sq. ft, then you need something in the region of an 8,000 BTU portable air conditioner. 

Ceiling height, air circulation, and heat and humidity can also reduce portable AC cooling performance, so we recommend choosing a slightly overpowered unit (within 500 BTU). 

If it turns out your portable AC is too small for your space, then this is something you may want to rectify. 

Likewise, a unit that is far too big for a room is an issue too.

It will cycle too quickly and continuously turn on and off, which consumes a lot of energy. It will also struggle to remove humidity due to the short cycle lengths.

7. Make Sure the AC is Unobstructed

Most portable AC problems related to cooling performance are due to an obstruction.

Check the vent and exhaust hose for kinks and blockages – if hot air can't escape the vent, the AC unit will not cool down your space correctly. 

Portable air conditioners also work best when placed at least two feet from the wall with no solid objects within two feet. 

If your portable AC is too close to walls and solid objects like sofas, cool air can blow back into the intake, reducing the amount of warm air removed. 

Choose the room where your portable AC will reside carefully – the less stuff in there, the better, and it might be worthwhile to clear things out. 

6. Stop Sunlight from Heating the Room

Direct sunlight streaming through windows and doors will heat your space, making it harder for your portable air conditioner to do its job. 

The easiest way to stop sunlight from heating the room is to install thermal blinds or curtains to reflect sunlight. This will reduce the greenhouse effect in your space, keeping it cooler, so your portable AC works properly. 

Products like solar control film can reject a high proportion of UV radiation and solar heat without blocking light. They also cut glare too.

5. Ensure any Room Leaks are Blocked

Room leaks will destroy the performance of your portable air conditioner by pulling out all that cold air. Warm air will enter your room, and your air conditioner will work doubly hard to do its job, usually with a significant performance drop (and a reduced lifespan). 

The best way to find leaks is to feel for them with a wet hand – wet your hand and feel around windows and doors for the sensation of air rushing past. If you feel the air on your hand, that leak needs fixing as soon as possible. 

Use acrylic sealant on frames to plug gaps and insulation strips inside to create an airtight seal where windows and doors meet the frame. 

Exposed floorboards can also leak heat. The best way to seal floorboards is by plugging them with foam strips that are not visible when pushed down. If you have air coming up through the carpet, check the underlay for gaps.

4. Check for Exhaust Air Leaks on Your AC Unit

If your portable air conditioner has an exhaust leak, warm air will escape the exhaust system and re-enter your room, reducing the cooling performance. 

Check the exhaust hose and connection for any signs of a leak. You can usually feel a leak with a wet finger, or you can spray some leak detection smoke into the air conditioner and see if any of it escapes the hose and vent system. 

3. Inspect the Exhaust Hose Positioning

Exhaust hoses work best when they are short and straight. If your portable AC's exhaust hose is bent, long, or winding, consider repositioning the portable air conditioner or replacing the hose with one that is straight. 

Avoid kinking and bending your exhaust hose too much – two bends are the maximum so that hot air can travel through it freely. 

2. Clean the Filters

You should clean your portable AC's air filters at least once per month, and if you live in a humid state like Florida, once every two weeks is better. 

Dirty, clogged air filters reduce an air conditioner's cooling performance by reducing the amount of air it can intake.

They are also a breeding ground for bacteria, odors, and mold, which can trigger allergens and asthma attacks.

To clean an air filter, remove it from the portable AC and spray it with a canister of compressed air outside. 

Then submerge it in a disinfectant solution and leave it for twenty minutes before cleaning it with a soft brush. 

1. How's the Positioning?

Portable air conditioners are powerful little machines, but not even they can overcome improper placement.

An air conditioner close to walls, windows, and doorways will struggle to cool down your room effectively. 

We recommend placing your portable AC in the center of the room or at least two feet from the walls so the air intake can work properly. 

If you are tight on space and can't maintain the 2 feet rule, at least ensure there is nothing within two feet of the front of the unit. 

The Most Common Portable AC Issues

These are the problems with air conditioners that we see far too often.

Your Room is not Sealed Effectively

Portable air conditioners extract warm air from a room and condition a percentage of it, cooling the space. This cooling process works best when the room is sealed so that all the cool air stays in the room.  

When you have gaps (such as underneath your door and window frames), cold air rushes out, and warm air rushes in. This creates a constant, inefficient cooling cycle, and your air conditioner must always work extra hard. 

Your Portable AC Needs Cleaning 

Cleaning your portable air conditioner could solve your cooling issues, especially if you haven't cleaned it in several months. 

You should clean the following components:

  • Air filter (once per month or every two weeks in humid climates)
  • Evaporator coil (every two months or every month in humid climates)
  • Condensate tank (whenever you empty it)
  • Condensate drain line (every two months with a vinegar flush) 

If you get musty smells from your portable AC, this is a sign that it needs cleaning. 

Your Portable AC is Too Small for Your Room

One of the common issues we hear about is people buying portable air conditioners for small rooms and expecting them to cool larger spaces. 

While it would be lovely for your portable AC to cool two rooms instead of one, it can't work miracles!

It's crucial to specify the correct BTU power for your space. Generally, you need 20 BTUs for every square foot – i.e., 4,000 BTUs for 200 sq. ft. 

Improper sizing and load calculation will guarantee poor cooling performance, so it's better to have a slightly overpowered than an underpowered unit. 

Getting an AC unit that is much too big will perform badly too, so it's important to take your time to size a model carefully.

Your Unit Needs Replacing

Supposing your portable AC is several years old and has just started struggling to cool down your room.

In that case, it probably needs replacing if you can't find anything wrong with the ventilation, exhaust, intake, or air filter. 

Most portable air conditioners have a lifespan between four and six years. Factors that affect lifespan include climate, AC sizing, home insulation, the standard of maintenance, and personal preferences (such as running it 24/7 on maximum). 

Ultimately, nothing lasts forever. If the tips in this article don't help make your portable air conditioner colder, a replacement will be your best option. 

About the Author Paul Cathro

Paul is an ex-HVAC engineer with 5 years 'in the trade'.

He acquired in 2022 and aims to make it the internet's most comprehensive HVAC resource for small homes in the next few years.

You can learn more about Paul's story here.

Browse his published work on the website here.

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