There are a lot of expensive parts inside your heating and air conditioning system.

Compressors. Blower motors. Control boards. Coils. Refrigerant components.

But sometimes, problems with all that expensive equipment can start with something that costs around $10 or $15.

Your air filter.

I know. Changing your air filter isn't exactly exciting HVAC advice.

But after more than 20 years in this business, I've seen plenty of situations where homeowners were dealing with comfort problems, frozen coils, poor airflow or a system that wasn't operating properly, and one of the first things we found was a filter that was absolutely packed with dirt.

The filter itself isn't usually the expensive problem.

What happens when you ignore it can be.

Your HVAC System Has to Breathe

Your heating and cooling system doesn't just make hot or cold air. It has to move a tremendous amount of air through your home.

Air is pulled into the return, passes through the filter, travels across the heating or cooling equipment and is then distributed throughout the house.

That airflow is a critical part of how the system is designed to operate.

Now imagine putting a piece of cardboard over the return.

The equipment may still try to operate, but moving the amount of air it was designed to move becomes much more difficult.

A severely dirty filter can create a similar problem.

As dirt, dust, pet hair and other debris collect on the filter, resistance to airflow can increase. Eventually, the system may not be moving the amount of air it needs.

And that's when a cheap maintenance item can start contributing to bigger problems.

Can a Dirty Filter Really Freeze an Air Conditioner?

It can contribute to it.

During cooling, warm indoor air passes across the cold evaporator coil. The refrigerant inside that coil absorbs heat from the air.

The system needs the proper amount of airflow across that coil.

If airflow becomes severely restricted, the coil temperature can drop too low. Under the right conditions, moisture on the coil can begin freezing.

Once ice starts forming, airflow can become even more restricted.

Before long, you may have an air conditioner running but very little air coming from the vents.

I've seen homeowners look at a frozen system and assume they're low on refrigerant.

That's certainly one possible cause.

But refrigerant isn't the only thing we check.

Airflow matters.

A dirty filter, dirty evaporator coil, blower problem, duct restriction or other airflow issue can all play a role. That's why we diagnose the system instead of guessing.

Heating Systems Need Airflow Too

This isn't just an air-conditioning problem.

Heating equipment also depends on proper airflow.

With a furnace, insufficient airflow can cause temperatures inside the equipment to rise higher than intended. Modern furnaces have safety controls designed to shut the burners down if certain temperature limits are exceeded.

If you've ever had a furnace that seems to heat for a few minutes, shut down and then start again, an airflow problem is one of several things a technician may investigate.

Heat pumps need proper airflow as well.

No matter what kind of HVAC equipment you have, moving the correct amount of air is part of the equation.

What About the Blower Motor?

Your blower is responsible for moving air through the duct system.

When airflow is restricted, the blower system isn't operating under the conditions it was designed around. Exactly how a particular motor responds depends on the motor type and system design, which is why I don't like blanket statements such as:

"A dirty filter will burn up your blower motor."

Maybe you'll hear somebody say that online.

That's too simplistic.

What I can tell you is that excessive airflow restriction isn't something we want in an HVAC system. We want the blower operating within the proper airflow and static-pressure conditions specified for the equipment.

That's one reason our technicians pay attention to the entire system instead of simply looking at whether it's blowing hot or cold air.

Should You Buy the Most Expensive Filter?

Not necessarily.

This is another area where homeowners can accidentally create problems.

You walk into a store and see a basic filter for a few dollars and a premium filter promising to capture all kinds of tiny particles.

Naturally, you think:

The expensive one must be better.

Not always.

Higher-efficiency filtration can be great when the HVAC system and filter setup are designed to handle it. But some filters can create more resistance to airflow than others, particularly as they become dirty.

The goal isn't to buy the cheapest filter.

And it isn't automatically to buy the filter with the biggest number printed on the package.

The goal is to use the right filtration for your system and your home.

If you're unsure, ask your HVAC professional what filter your equipment is designed to use.

How Often Should You Change Your Filter?

You've probably heard:

"Change your filter every 30 days."

That's easy to remember, but real life isn't quite that simple.

I've seen in homes where a filter can look pretty rough after a month.

I've also seen homes where the filter lasts considerably longer.

How quickly yours gets dirty can depend on several things, including:

-The type and size of filter
-How much the HVAC system operates
-Pets in the home
-Number of people living in the house
-Dust and other conditions inside the home
-Home improvement or construction projects
-The filtration system installed with the equipment

Instead of blindly following a number printed on a calendar, check the filter regularly and learn what is normal for your home.

If you've never paid attention to it before, checking it monthly is a good place to start.

That doesn't necessarily mean you have to replace it every month.

It means look at it.

Over time, you'll get a much better idea of how quickly your particular filter loads up.

One More Thing: Don't Forget About the Filter

This happens more than you might think.

Someone changes the filter regularly for years.

Then life gets busy.

Three months becomes six months.

Nobody remembers exactly when it was changed.

Meanwhile, the HVAC system keeps running.

This is why something so simple deserves a spot on your normal home-maintenance routine.

Put a reminder on your phone.

Write the date on the filter.

Keep replacement filters somewhere you'll see them.

Whatever works for you.

It doesn't need to be complicated.

A Cheap Filter Doesn't Mean a Cheap HVAC System

Depending on the equipment in your home, replacing major HVAC components can cost hundreds or even thousands of dollars.

Your air filter may cost $10, $15, $20 or more depending on what your system uses.

That's why this is one of the simplest pieces of advice I can give a homeowner:

Don't neglect the inexpensive things that help protect the expensive things.

I'm not telling you that forgetting to change your filter once is going to destroy your HVAC system.

It probably won't.

I'm also not telling you that every HVAC breakdown can be prevented by changing a filter.

It can't.

But I am telling you that your heating and cooling system needs proper airflow, and allowing a filter to become severely restricted doesn't help anything.

Here's the Takeaway

Your HVAC system needs to breathe.

A dirty filter can restrict airflow, reduce comfort and contribute to operating problems that can eventually lead to a service call.

So check it.

And make sure you're using the right filter for your system.

If you're not sure what filter belongs in your system, how often you should change it, or whether an airflow problem is affecting your equipment, ask your Simmons One Hour All Pro Tech the next time we're at your home.

​Sometimes taking care of a $10 problem really can help you avoid a much more expensive one.