Short answer: Your upstairs is hotter because hot air rises, your attic radiates heat downward through the ceiling, and most single-zone HVAC systems can't independently control temperatures on different floors. In Las Vegas, attic temperatures reach 150–160°F in summer, turning your second-floor ceiling into a radiant heater. The fix depends on how severe the gap is — from free thermostat adjustments to duct sealing, zoning systems, or a ductless mini-split addition. Call The Cooling Company at (702) 567-0707 for a home comfort assessment.
Key Takeaways
- A 2–3°F difference between floors is normal. A 5–10°F gap is a fixable problem. Most Las Vegas two-story homes I walk into have a 6–8 degree spread between the first and second floors during peak summer. That's not how the system is supposed to work.
- Your attic is the biggest factor most people ignore. At 150–160°F, your attic is hotter than the surface of some deserts. That heat radiates through your ceiling and heats your second floor from above — even while the AC is running.
- Ductwork in the attic is the worst-kept secret in Las Vegas HVAC. In most homes here, the supply and return ducts run through the hottest space in the house. Leaky connections and uninsulated sections lose 20–30% of your cooled air before it reaches the upstairs rooms.
- Closing downstairs vents completely is a mistake. Partially closing them can help redirect airflow, but fully closing them increases duct pressure and can damage the blower motor.
- There are $0 fixes, $500 fixes, and $5,000 fixes. Start cheap. Solve what you can for free, then decide if the remaining gap justifies professional work.
The Conversation I Have in Almost Every Two-Story Home
I can't count how many times I've walked into a Las Vegas home where the first floor is a comfortable 74°F and the master bedroom upstairs is 82°F. The homeowner is frustrated. They've turned the thermostat down to 70. The AC runs nonstop. The downstairs is freezing. The upstairs barely budges.
They almost always say the same thing: "Is my AC too small?" And the answer is almost always no. The problem isn't the equipment — it's the physics of the house, the ductwork, and how the system controls airflow.
I've been solving this problem in Las Vegas homes since the mid-'90s, when the valley was exploding with new two-story construction. The builders back then — and honestly, plenty of builders now — install a single HVAC system with one thermostat on the first floor and expect it to evenly cool 2,500 square feet across two stories in 115°F heat. It doesn't work. Here's why.
Why It Happens: The Three Forces Working Against You
Force #1: Hot Air Rises (Stack Effect)
This is the one everyone knows, but it matters more than people realize. Warm air is less dense than cool air. In a two-story home, the warm air naturally migrates upward while the cooler conditioned air settles to the ground floor.
Your AC system is fighting this constantly. The conditioned air coming from the upstairs supply vents is immediately mixing with the warm air that's risen from below plus the radiant heat coming through the ceiling. Meanwhile, the cool air from those same vents is sinking toward the floor and eventually drifting down the stairwell.
In a home with an open floor plan and a two-story great room — which describes about half the homes built in Las Vegas since 2000 — this effect is amplified because there's a direct column of air connecting both floors.
Force #2: Your Attic Is an Oven
This is the factor specific to Las Vegas that makes our two-story problem worse than almost anywhere else in the country.
During a typical July afternoon, when the outdoor temperature is 112°F, the surface of your roof hits 170–180°F. The attic space below it reaches 150–160°F. That heat radiates downward through the ceiling joists and drywall into your second-floor rooms.
Your second-floor ceiling is essentially a low-grade radiant heater running all day long. The AC is cooling the air, but the ceiling keeps reheating it. It's like trying to cool a room while someone runs a space heater in the corner.
The fix for this is insulation — specifically, making sure your attic has enough insulation between the attic floor and your second-floor ceiling. Most older Las Vegas homes have R-19 to R-30 insulation in the attic. The current building code calls for R-38. The Department of Energy recommends R-49 for our climate zone. That gap matters.
Force #3: Ductwork Runs Through the Attic
This is the one that makes me shake my head on almost every service call. In most Las Vegas homes — even relatively new ones — the HVAC ductwork runs through the attic. The supply ducts that carry cold air to your upstairs rooms travel through 150°F attic space. The return ducts that bring warm air back to the system also run through the attic.
Every foot of duct that passes through the attic is losing cooling efficiency. A supply duct carrying 55°F air through a 155°F attic doesn't deliver 55°F air to the bedroom at the end of the run. By the time it gets there — especially if the duct has leaky joints, crushed flex duct sections, or deteriorated insulation — the air might be 65–70°F.
Multiply that across every upstairs supply vent and you start to see why the second floor struggles. The air is being pre-heated before it even reaches the rooms.
Our duct cleaning guide covers the maintenance side, but the bigger issue here is duct sealing and insulation — making sure the conditioned air actually arrives where it's supposed to.
The 8 Fixes — Ranked from Free to Full Upgrade
Fix #1: Thermostat Fan Setting + Ceiling Fans ($0)
Switch your thermostat's fan setting from AUTO to ON. This keeps the blower running continuously, which circulates air between floors even when the compressor isn't actively cooling. It doesn't solve the problem entirely, but it can reduce the temperature gap by 2–3°F.
Run ceiling fans in occupied upstairs rooms. Fans don't cool air — they cool people by increasing evaporation off the skin. A ceiling fan lets you feel comfortable at 78°F instead of 75°F, which reduces the perceived gap.
One caveat: running the fan on ON instead of AUTO will increase your electric bill by about $20–$40/month depending on your system size. It also means the air is constantly passing over the evaporator coil, which can reduce dehumidification in more humid conditions.
Fix #2: Partially Close Downstairs Supply Vents ($0)
This is the quick-and-dirty approach, and it works better than most people expect. By partially closing (not fully — never fully) the supply vents on the first floor, you increase the air pressure in the duct system and redirect more airflow to the upstairs vents.
Start by closing downstairs vents to about 50%. Live with it for 24 hours. If the upstairs feels better but the downstairs is now too warm, open them back to about 75%. You're looking for the balance point.
The important rule: Don't close them more than 50%. Fully closing vents increases static pressure in the duct system, which makes the blower work harder, reduces efficiency, and can shorten the motor's lifespan. You're redirecting airflow, not blocking it.
Fix #3: Seal and Insulate Attic Ductwork ($1,000–$3,000)
This is the fix that gives the most bang for the buck in Las Vegas homes. If your ducts are in the attic — and they almost certainly are — they're likely leaking conditioned air and absorbing heat from the attic space.
A duct sealing job involves:
- Pressurizing the duct system to identify leaks
- Sealing all connections with mastic sealant (not duct tape — actual duct tape is terrible for ducts)
- Wrapping accessible duct sections with R-8 insulation
- Repairing or replacing crushed, kinked, or disconnected flex duct runs
On an average Las Vegas home, proper duct sealing can reduce the upstairs/downstairs temperature gap by 3–5°F and cut cooling energy use by 15–25%. It's one of those improvements that pays for itself within two to three summers.
Fix #4: Add Return Air Vents Upstairs ($500–$1,500)
Most two-story homes in Las Vegas have one or two return air grilles — and they're both on the first floor. This creates a fundamental airflow imbalance: cool supply air gets pushed upstairs, but there's no efficient path for the warm air upstairs to get back to the system.
The warm air has to drift down the stairwell, through hallways, and eventually reach the first-floor return grilles. By the time it does, it's mixed with cooler first-floor air, and the thermostat — which is also on the first floor — reads a temperature that doesn't reflect the actual conditions upstairs.
Adding a return grille in the upstairs hallway ceiling creates a direct path for warm air to reach the air handler. The system "sees" the warm upstairs air, runs longer when needed, and delivers more conditioned air until the actual whole-house temperature drops.
Fix #5: Increase Attic Insulation ($1,500–$3,500)
If your attic insulation is below R-38 — and in homes built before 2005, it usually is — adding insulation reduces the heat transfer from your scorching attic into your second-floor rooms.
The most common approach is blown-in cellulose or fiberglass insulation added on top of the existing batts. A professional crew can insulate a typical Las Vegas attic in half a day. The improvement is immediate and permanent — your second-floor rooms feel cooler and your AC runs less.
NV Energy sometimes offers rebates for insulation upgrades. It's worth checking their current rebate and incentive programs before scheduling the work.
Fix #6: Install a Zoning System ($2,000–$3,500)
A zoning system is the most targeted solution. It adds motorized dampers inside your ductwork and a separate thermostat for each zone — typically one for upstairs and one for downstairs.
When the upstairs thermostat calls for cooling, the dampers redirect airflow to the upstairs ducts. When the downstairs needs cooling, airflow shifts downstairs. Each zone gets independent temperature control without installing a second AC system.
The system works with your existing HVAC equipment. A technician installs the dampers in the trunk line, adds a zone control panel, and mounts a second thermostat. The job takes a day.
Important note: Zoning works best with variable-speed or two-stage equipment. If your system has a single-speed compressor and blower, zoning can cause issues with airflow and static pressure when one zone is closed. A good installer will assess your system's compatibility before recommending zoning.
Fix #7: Add a Ductless Mini-Split Upstairs ($3,000–$5,500)
If one or two upstairs rooms are consistently the worst — usually the master bedroom or a room over the garage — a ductless mini-split provides dedicated cooling without touching the existing duct system.
A mini-split is a small, independent AC system: a wall-mounted indoor unit in the bedroom connected to a compact outdoor compressor. It runs on its own thermostat, cools independently of the main system, and draws minimal power because it's only conditioning one room.
In Las Vegas, mini-splits are especially effective for:
- Master bedrooms that face west (afternoon sun)
- Bonus rooms over garages (zero insulation between the garage ceiling and the room floor)
- Home offices where someone needs consistent temperature all day
The main system handles the rest of the house. The mini-split handles the problem room. No more running the whole-house AC down to 68°F just to get the master bedroom to 75°F.
Fix #8: Upgrade to a Variable-Speed Two-Stage System ($6,000–$14,000)
If your system is 12+ years old and the upstairs problem has been there since day one, a full system upgrade with modern equipment can solve it at the source.
Variable-speed systems adjust their output to match the actual cooling load. Instead of running at 100% power until the thermostat is satisfied and then shutting off completely, they run at 40–70% most of the time and ramp up only when needed. This produces more consistent temperatures throughout the house, better dehumidification, and lower energy bills.
Pair that with a zoning system and proper duct sealing, and you've eliminated the upstairs/downstairs problem entirely.
This is the most expensive option, but if you're already facing an AC replacement in the next few years, it's worth solving the comfort problem at the same time rather than replacing old equipment with the same single-stage technology that caused the issue in the first place.
The Fix I Recommend Most Often
For most Las Vegas homeowners with a two-story comfort gap, I recommend starting with Fix #1 and #2 (free), then jumping to Fix #3 (duct sealing) if the gap is still more than 3–4°F.
Duct sealing is the unsexy answer. Nobody gets excited about sealing ductwork. But in 35 years of doing this, it's the single most effective improvement per dollar spent in our climate. It addresses the root cause — conditioned air being lost and heated in the attic — rather than masking the symptom.
If the gap persists after duct sealing, Fix #4 (adding returns) or Fix #6 (zoning) are the next steps, depending on budget and how the home is laid out.
Frequently Asked Questions
Is it normal for the upstairs to be warmer than the downstairs?
A 2–3°F difference is normal and expected in a two-story home. Anything beyond that — especially a 5°F+ gap — indicates a solvable problem with airflow, insulation, or system design. If your thermostat reads one temperature but certain rooms feel much different, there's something specific causing it.
Will a bigger AC unit fix the problem?
Almost never. An oversized AC system short-cycles — it cools the first-floor thermostat location quickly, shuts off, and never runs long enough to push adequate air to the upstairs rooms. In some cases, oversizing actually makes the upstairs/downstairs gap worse. The right approach is proper airflow distribution, not more tonnage.
Does closing the downstairs vents damage the system?
Partially closing them (50%) is fine and can help. Fully closing multiple vents creates excessive static pressure in the duct system, which can strain the blower motor and reduce efficiency. Use it as a temporary adjustment, not a permanent solution. If you find yourself closing half your vents to get the upstairs comfortable, there's an underlying ductwork or system design problem worth addressing.
Can I put the thermostat upstairs instead?
You can, but then the downstairs will be too cold because the system will run longer to satisfy the warmer upstairs reading. The real solution is a zoning system with thermostats on both floors so each area is controlled independently.
How do I know if my ducts are leaking?
If you can access your attic, look at the duct connections — especially where flex duct meets rigid duct or where ducts connect to register boots. If you see gaps, disconnected sections, or duct tape that's peeling away, those are leaks. A professional duct pressure test (called a duct blaster test) measures exactly how much air your system is losing, expressed as a percentage of total airflow. Anything above 15% leakage warrants sealing.
Ready to Fix the Upstairs Problem?
If you've tried the free fixes and the gap is still there, give us a call. We'll do a full assessment — measure the actual temperatures in every room, check your duct system for leaks, evaluate your insulation levels, and give you options ranked by cost and effectiveness. No guesswork.
Call (702) 567-0707 or book online. We serve Henderson, Summerlin, North Las Vegas, Green Valley, Enterprise, and all surrounding neighborhoods. NV License #0075849.