Essentially, most homes will have at least two air filters, because most homes have a return duct to go along with their air handler. Determining how many filters your home needs is a big step in helping improve your home's indoor air quality and keep you breathing easy.
Typically, a house will have 2 air filters in their intake vents.
Do I need both a furnace filter and a return air filter? Most HVAC systems only require one filter, usually located at the return air vent, to capture particles before the air reaches the furnace or AC.
You will need to open both the top and bottom doors to get to the filter. Vertical HVAC unit with air moving downwards - Your air filter will be in the top door, where the blower is located. This type of furnace or AC unit will most likely require two filters.
Essentially, most homes will have at least two air filters, because most homes have a return duct to go along with their air handler.
Tip: If you're looking to replace your outside AC unit filter, the filter location varies depending on the unit. However, it can usually be found along the air conditioner return duct.
What problems can a backward filter cause? The most common thing you will notice is the inefficiency of the filter. It will be harder for the air to flow, which would take a toll on your system. More strain means spiked utility bills.
For 1- to 2-inch filters, replace them every 1 to 3 months. For 3- to 4-inch filters, replace them every 6 to 9 months. For 5- to 6-inch filters, replace them every 9 to 12 months.
While return vents don't always require filters, adding them provides additional filtration, improving indoor air quality and keeping dirt and debris out of your system. However, there are pros and cons to consider.
Filters with a MERV rating of 1 to 7 typically cost between $5 and $20. Filters with ratings of 8 to 13 can cost anywhere from $20 to $150. HVAC systems in residential homes usually don't need (and often cannot handle) filters with a MERV rating of more than 13.
First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.
HVAC systems in larger homes tend to have more than one air filter. After locating the first one at your air handler, you'll want to check for a second filter at your return vent. The return vent will have a filter that will be much larger than your normal vents.
You need 1 “set” of filters, 1 filters air intake to the blower unit & 1 on the return to filter house air.
This leads to a variety of issues for your HVAC system including system inefficiency, higher energy bills, inadequate air quality, and ultimately failure. If you haven't been swapping your air filters as frequently as you should, there's no time like the present to start practicing this crucial maintenance step.
After replacing the filter, you should wait at least 12 hours before running the system. If the AC is still not blowing cold air, it could signify that you have a refrigerant leak, a damaged condenser, or your entire mechanical system needs maintenance.
The first thing you'll want to do is shut off your HVAC system. You should always avoid changing furnace filters while running the heating system, as various types of debris can enter the furnace — and you certainly don't want that to happen.
What if there is no arrow on the air filter? If there's no arrow on your air filter, just make sure the side with the frame (usually the cardboard or metal side) faces the furnace. The flat side of the filter should face the return air duct.
The structure of an air filter is such that one side is typically more porous than the other. This difference is not just a manufacturing trick — it's a deliberate design to maximize the filter's efficiency. The more porous side is crafted to face the incoming air, allowing it to capture airborne particles effectively.
You might wonder about the risks of running your AC without a filter, even temporarily. The simple answer is: not for long. Ideally, your AC should never operate without a filter for more than 6-8 hours. Going beyond this can negatively affect both your system's health and your home's air quality.
Where Is My Furnace Filter Located? You'll frequently find the air filter within the blower compartment, which is accessible through a metal door or hatch on the bottom half of the furnace. It may also be in a sliding compartment by the air handler component of your furnace or on a rack placed on the furnace's side.