Common HVAC Myths That Cost Homeowners Money

When you live in the Valley, running the air conditioner is one of the largest expenses in your household budget. Because of that, homeowners are always looking for ways to keep their homes comfortable without dreading the monthly utility bill.

You’re already doing everything you’ve been told — and your electric bill is still brutal. Here’s why: most of that advice is wrong. But here is the frustrating truth: a lot of the “common sense” advice passed down from your neighbors or read on old forums is completely wrong. In fact, many of these “money-saving” hacks are secretly destroying your air conditioner and driving your electric bills higher.

Let’s bust the 8 most common HVAC myths that are costing you money, so you can keep your home comfortable without draining your wallet.

Myth 1: Closing Vents in Unused Rooms Reduces Your Energy Bill

This is the number one myth we see, and it’s a killer. It makes logical sense—if you aren’t using the guest room, why pay to cool it?

The Reality: Your HVAC system is not a smart speaker; it doesn’t know you closed a vent. It pushes the same amount of air regardless. When you close vents, you disrupt the balanced airflow the system was designed for. This creates high “static pressure” inside your ductwork.

Think of it like blowing air through a straw and then pinching the end. That back-pressure strains your blower motor. Over time, that strain leads to a premature (and expensive) motor failure. Plus, that trapped air often forces its way out of small cracks in your ductwork, meaning you are literally paying to air-condition your sweltering Arizona attic.

Myth 2: A Bigger HVAC System Always Performs Better

If a 3-ton AC unit cools your house well, a 5-ton unit will cool it faster and better, right? Wrong.

The Reality: An oversized HVAC unit is a massive problem. If your system is too big for your square footage, it will cool the house down in 10 minutes and shut off. This is called “short cycling.”

Because the unit turns off so quickly, it never runs long enough to pull the humidity out of the air.
You’re left with a house that feels clammy and uncomfortable, even if the thermostat says 72°F. Worse, the continuous stopping and starting draws massive surges of electricity and wears out your compressor years before its time.

ENERGY STAR’s HVAC Quality Installation page is a good resource if you want to understand proper sizing and installation.

Myth 3: Cranking the Thermostat Makes the House Cool Faster

You walk into a hot house and immediately drop the thermostat to 60°F, hoping it will blast cold air faster.

The Reality: Your AC system only has one speed: ON. Setting it to 60°F won’t make it reach 72°F any faster than if you just set it to 72°F in the first place. All you are doing is guaranteeing the system will overshoot your target, freeze you out, and waste electricity when you inevitably forget to turn it back up.

The Fix: Invest in a smart thermostat. You can program it to manage your home’s temperature gradually, which is the true secret to smart thermostat efficiency.

Myth 4: You Should Turn the AC Completely Off When You Leave

The Reality: Turning the unit completely off allows the ambient heat in your home to build up unchecked—especially in our stucco homes that bake in the afternoon sun. When you get home at 5 PM and turn the AC back on, the unit has to work twice as hard to remove the dense heat from your walls, furniture, and carpets.

The Fix: Don’t turn it off; just set it back. The Department of Energy recommends setting your thermostat to 78°F or 80°F while you are away. This prevents the house from turning into an oven while still reducing AC usage.

Myth 5: You Only Need to Change Your Filter Once a Year

The Reality: If you wait a year to change your filter in Arizona, you are begging for a system breakdown. A dirty filter restricts airflow to the evaporator coil. In the summer, this lack of warm airflow causes the coil to literally freeze into a solid block of ice, shutting down your system.

Depending on how much dust gets kicked up in your neighborhood, whether you have pets, or if you run your system constantly, you need to change your filter every 30 to 90 days. It is the cheapest, easiest way to improve indoor air quality and prevent emergency service calls.

Myth 6: Ceiling Fans Actually Cool the Room

The Reality: Fans cool people, not rooms. They create a wind-chill effect on your skin that makes you feel up to 5 degrees cooler. But the actual temperature of the room doesn’t change a single degree. Leaving a ceiling fan running in an empty room is just adding to the reason why your electric bill is so high in the summer.

The Fix: Check your ceiling fan direction in the summer—it should spin counterclockwise to push air straight down. And remember: turn it off when you walk out of the room!

Myth 7: Run Your AC Until It Completely Dies

It’s tempting to try and squeeze one more summer out of a 15-year-old AC unit to delay the cost of an upgrade.

The Reality: It’s a false economy. The drop in efficiency and the constant $300 to $500 repair bills far outpace the savings of delaying a replacement. According to the DOE, upgrading to a high-efficiency HVAC replacement can save you 20% to 40% on your cooling costs.

Myth 8: Maintenance Is a Waste of Money Until Something Breaks

Why pay for an AC tune-up if the air is blowing cold?

The Reality: Think of your AC like your car. You don’t wait for the engine to blow up before you change the oil. A seasonal HVAC maintenance check is preventative. Cleaning the coils, clearing the condensate drain line, and checking the refrigerant levels prevents the system from overworking. Regular maintenance can extend your system’s life from 10–12 years to 15–20 years.

The Real Cost of HVAC Myths (At a Glance)

Stop Paying for Bad Advice Today

Operating your AC intelligently is the best way to keep your bills low. But while DIY habits—like keeping vents open and changing filters—are crucial, nothing replaces the eye of a certified technician.

If you are noticing signs your HVAC system is failing, like uneven cooling, strange noises, or bills that are suddenly much higher than last year, it’s time for a professional set of eyes.

“I wish I’d known about PlumbSmart years ago. Excellent service and reasonable pricing…also they have Free Estimates!” – Judy Anderson [Read full review]

“PlumbSmart is the absolute best.. great team, professional, experienced, and supportive.” – Joy Smith [Read full review]

At PlumbSmart, our certified techs don’t work on commission, which means we will never try to sell you a part you don’t need. We’re here to give you an honest assessment of your system’s health.

Your AC is working harder than it should — and you may not even know it yet. Our certified techs will tell you exactly what’s going on, no commission pressure, no upsell. Call (480) 992-2225 or schedule online — same-day appointments available.

Frequently Asked Questions: Debunking Expensive HVAC Myths

Does closing AC vents in unused rooms save money?

No, it does the exact opposite. Your AC system pushes the same amount of air regardless of open or closed vents. Closing them creates trapped back-pressure that can blow out your duct seams, strain your blower motor, and actually increase your electric bill.

How can I cool my house down faster when it’s hot?

Set your thermostat to your actual target temperature (like 72°F). Dropping it to 60°F won’t make the AC blow colder air or cool the room faster. Your AC only has one speed. Cranking it down just overworks the system and wastes energy when the house inevitably gets too cold.

What temperature should I set my thermostat while at work?

The Department of Energy recommends setting your thermostat to 78°F or 80°F while you are away. Never turn your AC completely off! Letting an Arizona house bake all day forces your system to work twice as hard to remove deep heat from your furniture and walls when you return.

Is a bigger air conditioning unit better for a hot climate?

Not if it’s too big for your home’s square footage. Oversized units cool the air too fast and shut off quickly—a problem called “short cycling.” This leaves behind clammy, humid air and wears out your compressor prematurely. Accurate sizing is much more important than sheer power.

Is annual AC maintenance really necessary if it’s blowing cold air?

Yes! Waiting for your AC to break is like waiting for your car engine to smoke before changing the oil. Routine maintenance catches cheap fixes early, extends the lifespan of your unit by years, and keeps your system’s efficiency high so your monthly bills stay low.