Most of these come up on real service calls. None of them are about people being dumb; they are bits of folklore that get passed around because they sound logical and no one has had a reason to push back. Here are the ones we hear most.
Myth 1: Setting the thermostat lower cools the house faster
An AC has a fixed cooling capacity rated in BTUs per hour. It is not "throttled" by the size of the gap between current and target temp. The compressor runs at the same speed (or, for variable-speed systems, ramps up the same way) whether you ask for 75°F or 65°F.
The actual effect of setting it 10 degrees lower than you want: the system runs past the point where you would have been comfortable, you forget to set it back, and you sit in a 65°F house wondering why your bill jumped.
Truth: Set it to where you want to end up. Be patient.
Myth 2: Closing vents in unused rooms saves energy
It feels intuitive: less square footage to cool means less work. The problem is your duct system was designed for a specific airflow. Closing registers raises static pressure, which:
- Forces the blower to work harder (uses more energy, not less)
- Reduces total airflow across the evaporator coil (can cause it to freeze)
- Stresses the blower bearings and motor (shortens life)
- Increases duct leakage at every joint (you blow more conditioned air into the attic)
Truth: If you really want to reduce cooling to specific rooms, install zone dampers (a real upgrade) or look at a multi-stage / variable-speed system with smart vents. Do not just close registers.
Myth 3: Bigger AC is better
An oversized AC removes more total BTUs per hour, which means it satisfies the thermostat sooner and shuts off. That sounds good and is actually bad. Reasons:
- The Houston AC's main job is removing humidity, which only happens once the coil is cold and runs long enough for moisture to condense and drain. Short cycles do not pull humidity.
- Each on-off cycle is the hardest moment on a compressor and motor. More cycles, faster wear.
- Comfort suffers because the house ends up cool and clammy instead of cool and dry.
Truth: Right-sized is best. A real Manual J load calculation looks at insulation, glass, orientation, infiltration, and occupancy, and gives you the actual size your home needs (almost always 0.5 to 1 ton smaller than a square-foot rule of thumb suggests).
Myth 4: A working AC does not need a tune-up
"It is cooling, leave it alone." We hear this every spring. The problem is that "cooling" and "running well" are not the same thing. A system can be:
- Down 20 percent on capacity from a slow refrigerant leak
- Drawing 30 percent more amps than spec because the capacitor is failing
- Pulling air through a clogged filter that is starving the coil
- Running with a 12 percent duct leak that is throwing 40 percent of your cooling into the attic
It is still cool inside, the bill is just higher and the system is wearing faster. A real tune-up catches all of those.
Truth: Annual tune-up is $99 flat. Saved capacity, lower bill, and catching problems early easily pays it back.
Myth 5: Filters last 6 months / a year / forever
It depends on the filter:
- 1-inch fiberglass (the cheap blue ones): 30 days. They start out poor and get worse.
- 1-inch pleated (most homes): 60 days, less if you have pets.
- 4-inch or 5-inch media filter (whole-home cabinet): 6 to 12 months. These are the right answer for most homes.
- HEPA add-ons: per manufacturer schedule.
Truth: Set a phone reminder appropriate to your filter type. Check it monthly during summer; if it is loaded, change it.
Myth 6: One room being too warm or too cold is "just how the house is"
It is not. The most common causes:
- Insufficient airflow to that room (closed register upstream, kinked flex duct in the attic, leaky duct)
- Heat gain the system was not sized for (a south-facing room with three big windows, a converted garage)
- A room far from the air handler with restrictive ductwork
Truth: A duct test and balance pass usually fixes it. Sometimes a small zone damper or a separate mini-split for a problem room is the right call.
Myth 7: A new high-efficiency unit will pay for itself fast
It depends. Going from 13 SEER to 18 SEER2 cuts cooling cost roughly 30 percent. On a $1,500 a year cooling bill, that is $450 a year saved. The variable-speed upgrade premium is usually $2,000 to $4,500. So the pure efficiency payback is 4 to 9 years.
That is reasonable, but it is not "pays for itself in 2 years" the way some sales pitches present it. Where a high-efficiency upgrade really wins is comfort (no more swings between cold and warm) and reliability over a 15+ year service life.
Truth: Efficiency matters, but it is one factor among several. Match the tier to your situation: how long you'll be in the home, how much your bills are, how much comfort matters to you.
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