Every House Has a Story

Sometimes Less Is More

You pull out the A/C filter and it looks terrible.

"Didn't we just change this thing?"

Maybe you did.

But there isn't one magic number that says an A/C filter lasts 30, 60 or 90 days in every house.

Think about two completely different homes.

One is a seasonal Florida home. Nobody has been there for two months. No pets. Windows and doors stay closed. The house is clean and the A/C is simply maintaining temperature and humidity.

The other has two dogs, a cat, four people, doors opening all day and plenty of life happening inside.

Those two filters are living very different lives.

Outdoor A/C condenser unit beside a Florida home

Add allergies, pollen, construction dust, remodeling, frequently opened doors and windows, and the difference can become even bigger.

So instead of only asking:

"How old is the filter?"

Sometimes the better question is:

"What has this filter been dealing with?"

Then there are the expensive filters.

Walk down the filter aisle and it's easy to think the most expensive filter must be the best one.

More filtration.

Smaller particles.

Better for allergies.

Sounds logical.

But an A/C also needs to breathe.

Generally, filters that capture increasingly small particles can also create more resistance to airflow. Whether that matters depends on the filter, its dimensions, the return-air system and the HVAC equipment it is installed in.

And once any filter gets dirty, airflow can become even more restricted.

That's why sometimes buying an appropriate, less expensive filter and replacing it more frequently can make more sense than buying the most restrictive filter on the shelf and trying to make it last as long as possible.

Sometimes less is more.

That doesn't mean high-efficiency filters are bad.

For someone dealing with allergies or other indoor-air concerns, better filtration may be very worthwhile.

But the filter still needs to be appropriate for the HVAC system.

The best filter isn't necessarily the one with the biggest number on the package.

It's the one that provides the filtration the homeowner wants while still allowing the system to receive the airflow it needs.

So what happens when airflow gets too low?

The evaporator coil inside the air handler gets cold.

Air needs to continuously move across that coil.

Restrict that airflow enough and, under the right conditions, the coil can become cold enough for moisture on it to freeze.

Now the A/C isn't happy.

Cooling performance drops.

The system may run longer.

Eventually someone may be standing in a Florida garage wondering why there is ice on an air conditioner when it's 90 degrees outside.

What about running without a filter?

That's another question where circumstances matter.

A clean, vacant seasonal house with no pets running briefly while someone gets the correct replacement filter is very different from operating a busy house with several animals for weeks or months without filtration.

Missing the filter for a short period isn't the same situation as deciding the system simply doesn't need one.

The problem is what happens over time.

Without the filter, particles that would normally be captured before reaching the equipment can continue farther into the system.

Eventually some of that material can accumulate on the evaporator coil.

Now you've basically created a dirty filter that you can't simply slide out and throw in the garbage.

Cleaning an evaporator coil is considerably more involved than replacing a filter.

That's why the filter isn't only there for the people living in the house.

It's protecting the equipment too.

So next time somebody asks:

"How often should I change my A/C filter?"

Maybe the answer starts with looking at the house.

Pets or no pets?

Occupied or vacant?

Doors and windows constantly opening or mostly closed?

Construction or remodeling happening?

Someone with allergies who wants better filtration?

And what kind of filter was the HVAC system actually designed to handle?

A filter is one of the simplest components in the entire house.

But sometimes it can tell quite a story about what's happening inside.

There's Always Another Story

I've walked into a lot of homes over the years.

Every one of them has taught me something.

This is just one of them.

– Carsten

Curious what else gets a look during a visit? Here's what I check on every Home Watch visit, including the air handler itself.

Read another story: The Hissing in the Wall

The A/C Trilogy

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