After paying close to $10,000 for a new HVAC system, a Dallas-Fort Worth homeowner still watches the indoor temperature creep up in the late-afternoon heat.
At the hottest part of the day, the house shifts from 72 degrees Fahrenheit to 77 or 78, leaving the owner wondering what acceptable performance is supposed to look like after a major install.
Here's what to know
On Reddit's r/hvacadvice forum, the homeowner said a full HVAC replacement was installed in a 1,600-square-foot single-story house, using a 4-ton unit and an Ecobee thermostat. Even after several return visits from the contractor for refrigerant adjustments and a TXV replacement, the problem has not fully disappeared during peak heat.
"If I set it to 72, it'll hold that for most of the day," the original poster wrote. "But during the hottest 3 to 4 afternoon hours, it'll drift up to 77 or 78 and stay there until the sun starts going down. One day with 6 guests coming in and out, it hit 79. I understand extra load matters. I'm not expecting miracles like pulling a hot house down to 72 in the middle of a 105 degree day. But if it's already at 72 all day, I do expect it to stay there, and that's the part I'm unsure about."
One commenter said the system could not really be judged without more technical information, including "pressures, duct size, supply locations, return locations, static pressure readings, temp splits, sub cooling" and more.
Others thought the bigger issue might be the house itself, with one commenter writing, "Sounds like an insulation issue not AC. The heat is penetrating through the windows or roof or something."
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Even an expensive HVAC install can underperform if the home itself is letting in too much heat.
More background
Much of the discussion focused less on the new condenser or thermostat and more on the building envelope. Rather than assuming replacement equipment would solve everything, commenters repeatedly pointed to insulation, older windows, leaky doors, return-air design, and overall airflow through the house.
Others noted that 4 tons for 1,600 square feet might sound large in some regions, but sizing depends heavily on local climate, sun exposure, insulation quality, and whether the installer actually performed a load calculation.
If the real issue is air leakage or poor insulation, the AC may have to work harder during the most expensive hours of the day, using more electricity without cooling the home.
What can be done?
Instead of more trial-and-error part swapping, commenters suggested getting clearer diagnostics first. Useful data includes refrigerant readings, temperature split, static pressure, and confirmation that the ductwork and return air are adequate for the house.
Extreme temperatures can expose weaknesses in the house as much as weaknesses in the equipment. Attic insulation, air sealing, west-facing windows, and older doors can all increase heat gain, making even a new system struggle. An energy audit can help identify which upgrades would make the biggest difference before spending more money on HVAC parts.
"My question is, is a 3 to 4 degree rise during peak heat considered normal in DFW, or should this system be doing more?" the OP wrote. "What measurements would you want to see before saying, 'Yep, this is performing correctly.' I want to be fair to the contractor, but I also want to know if my expectations are reasonable."
Where can I learn more?
When a brand-new system still cannot keep up with brutal afternoon heat, the answer may have as much to do with the house as the equipment. The stories below look at costly replacements, thermostat tradeoffs, and a few practical ways people try to stay comfortable while using less energy.
• In Texas, an 82-degree house turned an AC recharge into a $9.7K replacement.
• Across the U.S., 78 degrees is the best setting to balance comfort, bills, and strain.
• In Delaware, this ceiling fan switch helped rooms feel cooler as temperatures neared 100.
The bigger point is that replacing the AC alone does not always solve a cooling problem. For homeowners trying to figure out whether a new system should really hold 72 degrees, that context can help clarify what to check next.
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