Just because the Air Conditioner is blowing cold air doesn’t mean your home will always feel as cool as you prefer. Learn how insulation, ductwork, ceiling height, windows, shade, and more all impact home comfort, especially in Southern California homes.
When people talk about air conditioning, the first thing they think of is the machine itself—the outdoor condenser, the thermostat, maybe the brand name. But the truth is, cooling a home is a systemic process. It’s not just about the unit. It’s about how the entire house is designed, built, and maintained to support that cool air you’re expecting in July.
As home inspectors, we test whether cold air is coming out of the registers. We verify whether the system is operational at the time of inspection, and we document any instances where it isn’t. But here’s what we don’t do—we don’t wait around for hours to see if your 2,500-square-foot home eventually cools down to 72 degrees evenly in every room.
Why? Because even a perfectly working air conditioner can struggle under certain conditions. Picture a large open-concept living room with 14-foot ceilings, minimal insulation, sun beating through a wall of west-facing windows with no shades, and leaky doors letting hot air creep in. The A/C could be brand new and functioning exactly as designed—and still, that space may take hours to cool down. That’s not a failure of the unit. That’s just basic science.
Insulation is the biggest factor
More than any of the factors below, insulation plays the biggest role in how well your house retains cool air in the summer. Most homes in Southern California built before 1978 have little or no wall insulation. Even after California’s energy efficiency standards (Title 24) went into effect, enforcement was inconsistent through the 1980s and 1990s. So unless a home was built in the 2000s or has been upgraded, there’s a good chance the walls of your home lack any insulation.
My mid 1960’s built home has no insulation in the walls and very minimal insulation in the ceiling. In fact, most of the insulation in the ceilings I added over time after I moved in. It is not uncommon for us to find homes with very little to no insulation in the attic. But even if the attic is heavily insulated, the walls usually are not. This means heat is entering the home and cold is escaping right through your walls.
It’s a Whole House System
Cooling performance isn’t about one piece of equipment—it’s about a bunch of moving parts working together:
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Ductwork design: Poorly laid out or undersized ducts can choke airflow. And depending on the code cycle when the home was built, some rooms—like bathrooms or kitchens—may not have ducts at all. It wasn’t always required. Unless someone spends a lot of money to run new duct work, generally when a system is installed, they either reuse the same duct work, or at least the same paths.
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Ceiling height: Heat rises. People love the look of tall ceilings. However, the taller the ceiling, the harder it is for a room to cool. My living room is always warmer than the bedrooms in my house.
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Windows: Good windows matter. Double-paned, properly sealed windows reduce heat gain. Old, single-pane or poorly installed windows let the heat right in. Unfortunately, we see a lot of newer windows poorly installed.
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Window placement: South- and west-facing windows take the brunt of afternoon sun. Even great windows can struggle without shading. Most people want big bright windows that let natural light in the house. But natural light comes at a cost in the summer when blaring heat is shining through those windows.
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Doors and seals: Gaps around doors leak cool air out and let hot air in. It adds up.
The Outside of Your Home
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Tree shade: Mature trees can significantly reduce solar heat gain. A home in full sun will naturally be warmer than one protected by shade. At my own house, we have a giant tree that needs to be trimmed regularly. I have learned it’s best to trim the tree in the fall, after the summer heat. If I trim the tree in the spring, my house is significantly hotter in the summer. Shade matters!
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Hardscape vs. softscape: Concrete patios and stone walkways absorb and radiate heat toward the home. Grass and plants absorb less heat and help regulate temperature. Many homeowners have gravitated to hard scapes to save on water. However saving on water can reflect more heat into the home. A lush lawn eats up your water bill, but will help keep your structure cooler.
Two-Story Homes Affect an Air Conditioner
If the home has two stories, the upstairs is almost always going to be warmer than the downstairs. That’s not a sign something is broken—it’s just how heat behaves. It’s basic science 101,
During inspections, we check for air coming out of the registers upstairs and assess airflow balance. But we’re not testing for how comfortable it feels over time—we’re testing whether the system is working and delivering cold air. The fact remains the downstairs will likely always feel cooler than the upstairs.
Other Hidden Factors That Impact an Air Conditioner
Want to know why a house still feels hot even when the air conditioner is working? Here are a few more culprits:
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Thermostat location: If it’s in direct sun, near a kitchen, or by a drafty window, it may give false readings that throw off the entire system. For example, in my own home, the thermostat is located in a small hallway just outside the living room. Logically it makes sense for how the house flows, as it’s convenient to both the front door and leading to the bedrooms. However, this hallway has lower ceilings than the living room or bedrooms. This hallways also has no windows. The result? The temperature in the house is never the same as it says on the thermostat.
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Return air flow: Without enough return vents—or if they’re blocked—the system can’t circulate properly. Think of it like trying to breathe through a straw. While on new homes return vents are often in a ceiling, on older homes returns are often at floor level. This means sometimes someone puts a couch or table in front of the return, which restricts air flow.
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Closed interior doors: Closing doors can trap warm air and mess with circulation.
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Dirty filters: A clogged air filter means less airflow and less efficient cooling. It’s an easy fix, but often the most common reason an air Conditioner does not feel as cool as it could.
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Window coverings: Bare windows or light curtains don’t do much to block heat. Thermal shades and blackout curtains can make a big difference.
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Exterior materials and colors: Dark stucco, tile roofs, and large concrete areas absorb and radiate heat. Light colors and reflective surfaces help reduce that.
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Attic ventilation and whole-house fans: Poor attic ventilation can trap heat that radiates down into the living space. A whole-house fan or well-vented attic can offload a lot of that heat.
Final Thought
We inspect homes as systems, not just as a checklist of stuff. A lot of factors go into how comfortable a home feels when the air conditioner is running. That is why we look in the attic, check accessible windows, and more, on top of the condition of the air conditioner itself. But even the best-designed systems can’t overcome basic physics: heat rises, cold air sinks, and heat always moves toward cooler spaces.
Book your home inspection now by calling 818-298-3405 or book online here