Why Is My Upstairs 10 Degrees Hotter Than Downstairs and How Do I Fix It?

Heat rises, so it might seem like common sense that your upstairs is warmer than your downstairs. However, if there’s a big difference between the two, that uneven cooling might have less to do with thermodynamics than other factors.

If you’re in Henderson or Summerlin, there’s a good chance your home was built during the valley’s expansion boom of the 1990s and 2000s, when the dominant design aesthetic was volume: vaulted ceilings, great rooms open to the second floor, west-facing windows that capture the full force of an afternoon sun that in summer doesn’t set until well after dinner. Yes, those are beautiful design choices, but they also created one of the more challenging environments for a residential HVAC system.

The Duct System

Most residential duct systems are designed to a national standard. Unfortunately, Las Vegas is an extreme outlier. When outdoor temperatures reach 115°F, and your west-facing, second-floor bedrooms are soaking up hours of direct solar radiation through their windows and roof, the heat gain in those rooms can exceed what the duct design can handle. The result is a system that handles the downstairs fine while undersupplying the upstairs.

Start by checking your upstairs supply registers. Are they open? Is air actually moving through them? Hold your hand near one while the system is running. If the airflow feels weak or barely noticeable, you may have an undersized supply run (or there may be a blockage or kink in the duct).

Duct Leakage

In attic-based duct systems (most of the homes in the Las Vegas Valley), the ducts run through a space that can reach 150°F or more in the summer which accelerates aging for your ducts. Joints separate, insulation degrades, and the foil facing on the duct insulation cracks and pulls away. Over time, a lot of your conditioned air escapes into the attic.

The average home loses 20 to 30% of conditioned air to duct leakage. In Las Vegas attics, that number can be higher. If your upstairs is always a lot warmer, a duct inspection should be high on your to-do list.

Architecture Issues

Those west-facing windows in your upstairs bedrooms look great, but they’re big problems. Glass transmits solar radiation that wall insulation can’t counteract. A west-facing window with standard double-pane glass can allow hundreds of BTUs per hour into a room during peak sun exposure. Multiply that across several windows and a lightly insulated roof deck directly above, and you’ve got a heat load that hits in the late afternoon and doesn’t fade until well after midnight.

You can fix that without structural changes. Cellular shades or solar film on west-facing upstairs windows can cut solar heat gain, and attic insulation upgrades can reduce how much heat migrates from that 150°F attic space into your living areas.

What about Zoning?

If you’ve checked for duct issues, improved insulation, and managed window heat gain, and your upstairs is still hot-hot-hot, it may be time to think about the system’s design. Chances are good that you have just one thermostat for your entire home. That’s not great in a climate like Las Vegas’s.

Zoning systems divide your home into independently controlled temperature areas, each with its own thermostat and dampers that regulate airflow to that zone. The upstairs can call for cooling without over-conditioning the downstairs.

If you’re not sure where to start, a professional inspection should be your first step. It gives you a clear picture of where your home is losing the battle against the heat, so any changes you make go toward the actual problem. Talk to us about maintenance, whole-home comfort solutions, or even new AC installation.