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If you’ve got a furnace in the house, the clogged filter might bother you every 2-6 months and ask for a new replacement. 🙂 Several size variations are available when you’re up for buying one.
You can get 1 inch, 2 inches, 4 inches, and even thicker for the same length and width. And all of them will fit your furnace. But are they all equally good for you?
We’ve taken this particular question to break it down with an elaborative answer. For instance, we’ve put a 4 Inch vs. 1 Inch furnace filters comparison. But in a broad sense, it’s a ‘thin filter vs. thick one’ comparison.
4 Inch vs. 1 Inch Furnace Filters – Why Compare?
It’s known that the standard furnace filter dimensions (length and width) don’t have anything to deal with its efficiency. But the thickness of the filter largely impacts efficiency.
And that brings us to a head-to-head comparison between 1 vs. 4-inch furnace filters before you select the next filter replacement.
Some of us might find affording a 4 inches filter in every 3-4 months quite expensive. So, they might come up with an idea to replace the thicker(4”) one with a thinner(1”) inch alternative. This way, the replacement cost might be reduced to 50% or even higher.
Doing so, is the swapping going to work? Or it’ll take a much bigger toll of affecting the entire furnace?
4 Inch vs. 1 Inch Filters for Furnace: Head to Head
So, what are the differences between 1-inch and 4 inch furnace filters?
- The static pressure.
- System efficiency.
- Changing interval.
- Pollutant size (MERV Rating Range).
- Cost.
The Static Pressure
If we compare two filters of 1” and 4” thickness that sport the same MERV rating, there’ll be no difference in regards to the dirt size that’ll be filtered. But what will differ most between them is the ‘Furnace Filter Static Pressure’ on the system.
How?
A 4 inches thick filter will feature more holes than a 1-inch one. So, it will be easier for the air to pass through and make itself less restrictive.
On the other hand, a thinner filter (1”) will be more restrictive and create more air pressure on it. Therefore, the air pressure on the other side of the filter will face a comparative drop. And that’s what we call a ‘Static negative pressure’ in the system.
The static pressure will result in more wear on the blower motor, which will eventually decrease its lifespan. On the other hand, with a 4” filter, the motor lifetime will have a certain boost.
System Efficiency
Once again, if we put a 1-inch and 4-inch filter of the same MERV rating head to head, we will significantly impact the furnace efficiency.
In that sense, is 4-inch or 1-inch furnace filters better?
If you pass any given amount of dirty air through both of them, the number of ‘unclogged’ pores will be more in a thicker filter than a thinner one. Before being saturated, the thinner one will keep facilitating more airflow (CFM) through it than the thicker one.
The more CFM of air hits the furnace system, the more area it can cover with either heating or cooling action. In other words, the efficiency will be up to par. On the contrary, the efficiency will drop faster if you occupy a 1-inch filter beforehand.
Furnace Filter Change Interval
The next factor that might bother you is how often you change the filter. Roughly, the thinner a filter is, the less often you need to change the filter. But to be specific, three factors determine this frequency-
- The capacity of the filter to hold dirt particles.
- The airflow(CFM) through the system.
- The amount of dirt in a given amount of air.
The 2nd and 3rd factors are independent to the filter size and type in the furnace. But the first one is very closely related to the dimension of the filter. And by dimension, we mean all length, width, and thickness.
Irrespective of the length and width, the thickness determines the filter’s surface area. Take pleated furnace filter surfaces as an example. More thickness will allow more pleats, which will induce more surfaces to trap the dirt.
Summary: The thicker the filter is, the more dirt it’ll be able to hold. And therefore, you can enjoy a wider span of replacing the frequency of the filter. The time of how often to change the furnace filter will be, therefore, be longer.
Example: A 4-inch filter should be changed every 6-12 months, where a 1-inch thick filter should be renewed every 1-2 months.
Pollutant size (MERV Rating Range)
Both 1-inch and 4-inch filters come up with a range of MERV options. And this will have it’s obvious impact on the air quality of the indoor ambiance.
So, what MERV does each support, and what contaminants will they be able to filter?
| Filter Type | 1-inch furnace filter | 4-inch furnace filter |
| MERV Range | 1 to 13 | 8 to 16 |
| Contaminants | Pollen, cockroach debris, spray paint dust, dust mites, dust mite debris, carpet fibers, sanding dust, textile fibers, mold spores, hair spray, cat and dog dander, dusting aids, fabric protector, pudding mix, legionella, lead dust, humidifier dust, auto emission particulates, milled flour, nebulizer droplets. | Most of the contaminants of 1-13 MERV rating + Bacteria, some viruses, cooking oil, most smoke and insecticide dust, droplet nuclei (sneeze), most paint pigments, most face powder. |
So what do we learn from the chart?
Firstly, 4 inches filters cover a higher range of MERV ratings, slightly overlapping with the 1-inch ones. With a 4” filter, you will get at least an 8 MERV rating. With higher ratings upto 16, you can put controls over super-micro contaminants like bacteria, viruses, and powdery particles.
On the other hand, 1 inch filters are decent enough for removing typical dust, pet danders and other particles of up to 3 microns in size.
At this point, we don’t have a clear winner. It’s mostly up to your air cleaning preferences.
Cost
When it comes to furnace filters, the cost can be split into two kinds-
- The purchase/renewal cost.
- The energy bills.
The Purchase/Renewal cost
Of course, the purchase cost will be higher for 4 inches than for 1-inch ones. The range is defined as $20-$30/unit.
Here are a few of our hand-picked furnace filters for both of the thicknesses-
Best 4 inches furnace filters-
- Budget pick: Nordic Pure 20x25x4 (MERV 12)
- Best of both worlds: Honeywell FC100A1037 (MERV 11)
- Best high-end: Nordic Pure 20x20x4(MERV 13)
On the other hand, the standard price for 1” furnace filter lies within $5-$15/unit range.
Best 1 inches furnace filters-
- Budget pick: FilterBuy AFB Silver (MERV 8)
- Best of both worlds: AIRx ALLERGY 16x20x1 (MERV 11)
- Best high end: Filtrete 16x20x1 (MERV 11) or AIRx HEALTH 20x25x1 (MERV 13)
The Energy Bills
As furnace filters are not electric components, they directly don’t pull electric power. But they have a passive role to play in your monthly electricity bill.
As long as both 4” or 1” are in new condition, and the CFM of the air passing through is fine, there won’t be a significant raise. But as soon as they start to saturate, the furnace motor starts to work harder.
A 4” clogged filter will put more stress on the motor than a 1” one. If you keep it unwashed or replaced, it’ll surely raise eyebrows at the month-end.
Frequently Asked Questions (FAQ)
Can I use a 1 inch filter instead of 4 inches?
If you are okay with more frequent replacement and little stress on the system, 1” filter can be a budget-friendly alternative of 4” filter.
Is A 4-inch or 1-inch furnace filter better for filtration efficiency?
Regarding durability and filtration efficiency, 4 inches filters are way better than 1 inch thin ones.
How often to change furnace filters of both 1” and 4” sizes?
For thin filters like 1”/2” ones, you might need to change them every 1-2 months. For their thicker versions(4”/5”), it’s 6-12 months.
Bottom Line
The clean and clear bottom line is, Size does matter, as long as it’s about the thickness of your furnace filter. From a price point, 1” furnace filters might save a few bucks of yours. But 4” or thicker filters are the ultimate bang for the buck. Also, it will give your furnace system better health and efficiency.
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.
The purpose of the filter is to protect the evaporator. HVAC guys tell me this all the time as they are replacing a fan motor that has prematurely failed. If you need a high merv filter for air purity because of breathing issues then buy an external air purifier device.
The higher merv ratings will impede the air so that the fan motor draws more current and will fail earlier. My 4 inch filters are minimum $80 and if I don’t have time to mail order the best deal on the internet then they cost $120 each. When the unit was installed they said the filter will last a year. But two months in and the airflow is so impeded I can’t get the house temp up to 65 on a cold day. So put in another $80-$120 filter. I don’t understand how someone can just use a 1 inch filter instead of 4 inch. The filter holder is made for a 4 inch. A one inch will just flop over. I would like to find something to modify my 4 inch opening to accommodate a 1 inch filter. But I find nothing. So my only choice is to disassemble the whole thing and do some metal work. I wish I had bought a heater with 1 inch filter. But apparently they don’t even make that anymore.