Can I Use 16x25x4 Instead of 16x25x5 Air Filter?

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Finding a 16x25x5 furnace filter can be hard sometimes. Most of the locals sell from 1 inch to 4 inches. 

So the question is, Can I use 16x25x4 instead of 16x25x5 air filter?

Turns out, I can use 16x25x4 instead of 16x25x5. The size matters to prevent bypassing airflow. As a 4-inch filter isn’t much thinner than a 5-inch filter, it can fit easily. If the fit is perfect, there’s very little possibility of airflow getting bypassed. But remember thicker filters have more filtration. 

Do you want more about this aspect? If you do, keep reading. You’ll get to know some interesting facts here. So, let’s dive right in!  

Can I Use a 4-inch Filter Instead of 5?

Now, you have to know how a furnace filter works. It basically helps in protecting your furnace from dust, hair, debris, and similar pollutants. You’ll also be able to have a healthy breathing air quality by having a filter.

4-inch filter

Going back to the filter’s thickness. Here, you should be concerned about how much airflow is bypassed. If it’s too much, it’s bad for the health of your HVAC.     

So, what happens in a 4-inch vs 5-inch air filter? Though there’s a 1-inch gap, you’ll see a 4’’ HVAC filter fits in a 5’’ slot. The air won’t bypass too much unless you have a different furnace size.

If you’re good to go with 16x25x4 filters, here are some of the highly recommended 4-inch filters by users like you-

However, if your Onix tubing has issues, the 4-inch filters won’t work properly. So, be careful about that part. 

Do Thicker Air Filters Work Better?

Yes, thicker air filters work better. But there’s a catch. 

Well, when we’re talking about replacing thickness, obviously we’ll think about performance. 

The reason people care about thickness is that thicker filters allow more filtration. Thick air filters last longer than thin ones. You have to think less about maintenance too! 

But in some cases, thinner air filters work the best. Suppose, your furnace has only 3 inches in thickness. In this case, going for a 3’’ filter would be the best idea instead of 5.

Just like in these cases, thinner filters are better than thicker ones. 

So, can I use a thinner furnace filter? Yes, I can. You can. Anybody can! But only if it matches right with the size of the furnace.  

When Should You Change Your Furnace Filter? 

As we’ve already learned, 16x25x4 and 16x25x5 filters are swappable. But when you should think about changing it and what should be the changing frequency?

furnace filter

Take a look at the average replacing times of air filters below-

Filter SizeTime of Replacement
1-2 inches every 1-3 months
3-4 inchesevery 6-9 months
5-6 inchesevery 9-12 months

So, you can see that it’s like a 3-month cycle depending on each size. 

Well, did you notice a 5-inch filter takes longer to replace than a 4-inch one? That’s right, the thicker your filter is, the more time it takes. 

What if My Air Filter is Too Big?

Having the wrong size filter can impact the performance of your HVAC. I’m not saying it’ll destroy your machine. But it’ll definitely bring some changes.

And you’ll know about this by going through the utility bill. The heating and cooling system will not work properly. The efficiency level will drop down. 

As a consequence, the furnace will heat for a longer/shorter period of time than expected.  

Eventually, you’ll know there’s something wrong. The airflow will go around the filter. It won’t pass through it as expected. As a result, the air won’t be purified at all. 

So, using too big air filters is not really recommended. Try to use filters that are closest to the slot size. And make sure to measure the perfect air filter size.  

Don’t worry, I already got the size sorted for you. Check out the next section to know what a filter size actually looks like. 

Understand Air Filter Sizes Chart

I want to clarify one thing here. Whenever you see something like 16x25x4 on a filter, it doesn’t represent the actual size.

Air Filter Sizes

To understand the actual size, you have to multiply each of the sides with specific numbers. It goes like this-

Height – multiply by 15 ⅞ 
Width –  multiply by 24 ¾ 
Depth – multiply by 4 ⅜

This measurement is true for filters in all types of sizes. It doesn’t matter how tall or wide the filter you’re using, simply multiply the numbers above. You’ll get to know the real measurements.

Here is an air filter comparison chart given below to make things more clear: 

Normal Size (inch)Actual Size (inch)

So, you can see the actual size varies. Knowing the real size will help you buy the correct air filters.

Frequently Asked Questions (FAQs)

Can I use a 1-inch filter instead of 5?

No, you can not use a 1-inch filter instead of a 5. The reason is that 1-inch filters have a small surface area compared to the 5’’ ones. Less surface space means your furnace filter will become clogged quickly. This means you’ll have to take more hassle using a 1’’ filter instead of 5. 

Is there really a difference in air filters?

Generally, there are no differences in air filters. All of them perform the same basic functions. They remove dirt, allergens, dust, and other micro-pollutants from the air. Basically helps you to breathe fresh air. However, high-rated filters need to be maintained well as they use more energy.    

Can an air filter be too thick?

Yes, air filters can be too thick. But it depends on the size of the furnace. The thicker your furnace’s filter is, the faster it’ll get dirty. Now, to determine if a pleat is thick or not, check the MERV ratings. Having a MERV rating of more than 13 means your filter is thick. 

Are 5-inch filters better?

Yes, 5-inch filters are better. The best thing about the 5-inch filter is that it ensures better airflow. When you have a bigger filter, you’ll have to deal with fewer pollutants. Having a wider filter will make the air more refined and fresh. Your home will have proper air circulation.  


So, did you get your answer to “Can I use 16x25x4 instead of 16x25x5?” I bet you did!

Make sure you maintain the right balance of air circulation. Other than that, you’re good to replace a 4’’ filter with a 5’’ one. 

That’s it for now. Have a good day!

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