When the Heat Won’t Quit

Heat waves are no longer rare events. Across the United States, Europe, Asia, and beyond, communities are experiencing temperatures well above historical norms. And the consequences go beyond discomfort. Extreme heat is a genuine public health risk, straining energy grids and sending people indoors in search of air conditioning.

What most people don’t realize, however, is that when it gets hot enough, your air conditioning system isn’t just working harder. It’s working less effectively. Understanding why is the first step to doing something about it.

Your AC Was Tested for a World That No Longer Exists

Every air conditioning unit sold in the U.S. carries an efficiency rating — SEER2, EER2, or cooling capacity in BTUs — that was determined under standardized laboratory conditions. Those conditions, established by AHRI Standard 210/240, use an outdoor temperature of 95°F as the benchmark.

The problem? In much of the country, during a heat wave, 95°F is a relief. When temperatures climb into the low-to-mid 100s, as they routinely do across the South, Southwest, and increasingly the Midwest, the unit you bought for its impressive efficiency rating begins to fall short of what’s on the label.

This isn’t a defect. It’s physics. Air conditioners work by moving heat from inside a building to the outside air. The greater the temperature difference between the refrigerant and the outdoor air, the more efficiently that heat transfer happens. When the outdoor temperature rises, that difference shrinks, and the system has to work harder to do the same job.

What the Performance Data Actually Shows

Independent research quantifies this clearly. Laboratory testing published in peer-reviewed literature found that a 20°F increase in outdoor ambient temperature, from the standard 95°F test point to 115°F, resulted in a 25% rise in compressor power consumption and a more than 13% decrease in total cooling capacity.

In practical terms: during a 115°F afternoon, your system is drawing significantly more electricity while delivering meaningfully less cooling than you’re paying for. The combination of higher energy consumption and lower output is exactly what drives summer utility bills to record highs and, in severe cases, pushes equipment to failure. During extreme heat, you’re paying more for less cooling.

The Rooftop Heat Problem Nobody Talks About

For commercial and industrial facilities with rooftop units, there’s an additional factor that makes all of this worse. The units themselves are absorbing solar heat on top of the ambient temperature.

In desert climates, where ambient air temperatures can reach 110°F and solar irradiance is intense, dark roof surfaces can exceed 200°F. Temperature differentials between rooftop surfaces in full sunlight and shaded air measurements have been documented to reach 70°F for surfaces lying directly on a dark roof. Based on field observations, external HVAC cabinet temperatures in direct afternoon sun can reach 180°F or more. That’s heat that gets added directly to the system’s cooling burden.

Shading outdoor units from direct sunlight is helpful where it’s practical, but for rooftop equipment, that’s often not feasible. That’s where surface-level solutions come in.

What You Can Actually Do

The good news is that several practical steps can meaningfully improve your system’s performance in extreme heat. Proper maintenance should always come first: clean coils, clear filters, and well-functioning components all help your system operate as close to its rated efficiency as possible under conditions for which it wasn’t strictly designed. Dirty coils or restricted airflow make everything worse, especially on hot days.

Beyond routine maintenance, two coatings from Energy Performance Solutions address the heat problem directly:

ThermalBlock is a ceramic-technology coating applied to HVAC cabinets, ductwork, and rooftop surfaces. It reflects 89% of visible light and rejects 87% of external heat gain, achieving a Solar Reflective Index of 108. For a rooftop unit baking under direct afternoon sun, ThermalBlock reduces the solar heat load added to the cabinet. Ultimately, it’s one of the most cost-effective ways to reduce strain on units that can’t be shaded.

CoilSafe is applied directly to condenser and evaporator coils, forming a thin (10–15 microns), covalently bonded, glass-like layer that protects against corrosion from salt air, industrial pollutants, urban smog, and other environmental stressors, without reducing heat transfer. When coils corrode, they lose effective surface area, which directly reduces the system’s ability to exchange heat. Cleaning and then coating coils with CoilSafe protects that surface area and keeps coils performing closer to their original specification between service intervals. It’s UV stable, meaning the coating itself won’t degrade under the same sun exposure that makes rooftop operation so demanding.

The Bottom Line

Extreme heat isn’t going away, and air conditioning systems weren’t designed with today’s temperatures in mind. But the gap between what your system was rated for and what it’s being asked to do in the real world hasn’t been fixed yet. Proper maintenance, attention to solar heat load, and protective coatings that preserve coil efficiency can all help close it, keeping your system performing better, lasting longer, and costing less to run when you need it most.

Want to find out what ThermalBlock and CoilSafe could do for your facility? Call 713-931-2735 to start a conversation.

Citation List

1. Air-Conditioning, Heating, and Refrigeration Institute (AHRI), AHRI Standard 210/240-2026 (I-P): Performance Rating of Unitary Air-conditioning and Air-source Heat Pump Equipment. ahrinet.org

2. Conde-Petit, D. et al., "The effect of high ambient temperature on the performance of an R410a air conditioner," ResearchGate (2014). researchgate.net

3. Strickland HVAC, "Extreme Heat and AC Performance: What Homeowners Should Know" (July 2025). stricklandhvac.com

4. AboutDarwin.com, "Does Outside Temperature Affect Air Conditioner? Complete 2026 Guide" (October 2025). aboutdarwin.com

5. Faramarzi, R. et al., "Performance Evaluation of Rooftop Air Conditioning Units," ACEEE Summer Study on Energy Efficiency in Buildings (2004). aceee.org

6. Calculator Academy, "Roof Temperature Calculator" (March 2026). calculator.academy

7. Polyglass, "Understanding Roof Surface Temperatures: How Sunlight, Air Contaminants, and Timing Impact Thermal Readings" (January 2025). polyglass.us

8. IEEE, "Effect of Rooftop Exposure in Direct Sunlight on Conduit Ambient Temperatures." ieeexplore.ieee.org