AC Unit Not Blowing Cold Air? It's Time to Change Your Filter

CNET

09-06-2025

Every year when I pull my air conditioner out of storage and reinstall it, I'm worried about whether my window unit managed to survive the colder months. This year when I turned it on, I was worried when instead of a cool breeze, my AC unit was blowing tepid air. I was braced for the worst and did the math on how much a new one would cost, but thankfully it wound up being a simple fix. I just needed a new air filter.
Once I pulled it out and saw the mess, it made sense. A dirty filter slows everything down and forces the unit to work harder, sometimes to the point where it stops cooling altogether. The fix? A quick clean or a swap for a new one, depending on your setup.
Now I make a habit of checking the filter regularly. It takes just a few minutes, but it keeps the air cold, clean and flowing. That's a lifesaver during these brutal summer months.
Below we'll outline when to change your AC filter and how to swap it the right way to guarantee your AC unit runs properly and efficiently. For more, explore these six ways to save on air conditioning this summer and effective ways to lower your AC bills when on vacation.
Read more: How to Clean Your Air Conditioner So It Runs Like New
Here's how to tell if your AC filter needs changing
The only real way to know it's time to replace your AC filter is by checking on it every so often. To do so, pop your AC filter out and hold it up to the light. If you can't see through the filter, then it's time for a new one. Below, find step-by-step instructions on how to change out your filter.
If your air filter looks like the filter on the left, then it's time to replace it.How to change an AC home air filter
First things first: You need to locate it. It could be several places: in the air handler cabinet, return air duct or in a window AC unit, etc.
Next, make sure you get the right filter size -- the dimensions are usually printed on the side of the filter – so you can make sure you're buying or ordering the right size replacement.
Now, it's time to actually change the filter:
Turn the power off . This will ensure that you don't touch live voltage or that debris be sucked into the unit. So, be sure to turn off power at the unit and also at the circuit breaker.
. This will ensure that you don't touch live voltage or that debris be sucked into the unit. So, be sure to turn off power at the unit and also at the circuit breaker. Remove the old filter. Simply slide it out of the slot that holds it in place.
Simply slide it out of the slot that holds it in place. Take note of its condition . Can you see through it when it's held up to the light? If not, definitely time to replace it.
. Can you see through it when it's held up to the light? If not, definitely time to replace it. Insert the new filter. To make sure you get it in the right way, make sure the arrow icon on the filter's frame points away from the return air duct and toward the air handler mechanism.
Buy the right size filter by checking the dimensions printed on the old filter's frame.
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How often does an AC filter need to be changed?
Do you know off the top of your head the last time you changed your filter? If you can't remember, it has no doubt been too long.
Many HVAC filters actually say on the packaging that a monthly check-in is ideal to keep dust and allergens to a minimum. For the most part, experts agree your filter will probably need to be replaced every three months or so, but monthly assessments can guarantee you don't leave a worn-out filter in your unit for too long past its effectiveness.
Other factors that change the lifespan of your AC filter
Depending on a number of factors, such as your surroundings, the season and the inhabitants of your home, you may want to replace your air conditioning filter more or less often than once a month.
Air filter type
Some air conditioning filters are made to last longer than others. But luckily, you don't have to do a ton of research or be an AC expert to know which brand is best. Just look at the packaging.
All AC filters have a Minimum Efficiency Reporting Value (MERV) rating. The higher the MERV number, the better quality the filter is, meaning it can hold contaminants or debris more efficiently and therefore lasts longer.
The only downside to picking a filter with a high MERV rating is that it can slow down the airflow in your AC unit. The best filter options will have a balance between good quality and good airflow, which is typically a filter with a MERV rating between 6 and 8. If you have a high-efficiency AC unit, you may be able to get away with a higher MERV rating, but check the owner's manual just in case.
Geography
Geography and seasonality can also affect how often your filter will need to be replaced. Living in a dusty or more polluted environment calls for a new air filter at least once every three months.
For example, in desert climates, your AC is filtering out all that desert dust (in addition to 90-plus degree temperatures) to keep the air in your home pleasant to breathe. Your AC is likely working overtime, which means it'll need extra maintenance.
Pets
What sort of creatures inhabit your household can also determine how often you'll need to replace the filter. If you're like me and have two long-haired pets living with you, checking your filter every three weeks is a good rule of thumb to prevent build-up.
Usage
If you live in a temperate climate and rarely turn your AC unit on, you can probably wait up to six months to change the filter. A simple way to remember is to switch the filter out once in the spring and again in the fall.
Watch this: Beat the summer heat with this DIY air conditioner
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An added incentive to change your filter
Not only can regularly changing your AC filter help improve your home's air quality and conditions, it can save you money over time. Replacing a dirty, clogged filter with a new, clean one can lower your air conditioner's energy consumption by 5 to 15 percent, according to the US Department of Energy. And less energy consumed by your AC equals lower utility bills, which is a huge perk in the heat of summer when electricity costs spike for much of the US.
For more, you can also check out this home upgrade that can save you money on AC costs and this comparison between window AC units and portable AC units.