September 8, 2026
News | September 7, 2026 | 2 min read
On September 2, the US Department of Energy authorized emergency backup generation for PJM Interconnection, the largest power grid in the country, as a late-season heat wave pushed demand toward record territory from Washington, DC, to Chicago. It was the last step before a Level 3 emergency alert, the stage that precedes rotating blackouts.
The lights mostly stayed on. But the episode is a useful reminder of something most homeowners never think about until it happens: when the power flickers or the thermostat goes up, your home stops filtering its air. Here's what actually happens inside a house during a grid event and what to do about it.
PJM, which serves 67 million people across the Mid-Atlantic and Midwest, issued a maximum generation emergency alert on the morning of September 2. Temperatures in Chicago, St. Louis, and Washington, D.C., were forecast to climb past 90°F during peak demand hours. Neighboring operator MISO projected peak demand near 121 gigawatts, within striking distance of its 127.1 GW all-time record.
Energy Secretary Chris Wright authorized backup resources, saying that "maintaining affordable, reliable, and secure power for hardworking American families and businesses during periods of hot weather is non-negotiable." Utilities went further down the chain. The Howell-Oregon Electric Cooperative in rural Missouri asked customers to unplug idle devices and raise their thermostats to cut air conditioning load.
Because your air filter only works when air is moving through it. A central HVAC system does not filter continuously; it filters when the blower runs. Raise the thermostat four degrees to help the grid, and you have also cut your filtration cycles for the day. Lose power outright and filtration stops completely, in a sealed-up house, on the hottest day of the week.
That is the part the conservation notices never mention. Reducing runtime is genuinely useful for the grid, and it is a real trade-off for the air in your living room. It is worth knowing you are making it.
Often, yes. Ground-level ozone is not emitted directly. It forms when pollutants from cars, power plants, and industrial sources react in sunlight, and the EPA notes it "is most likely to reach unhealthy levels on hot sunny days in urban environments." The same conditions that strain the grid are the conditions that build ozone.
One honest caveat, because it matters: MERV-rated HVAC filters are designed to capture particles, not gases. A high-MERV filter handles dust, pollen, and smoke particulates. It is not an ozone control. If odors are your concern, an activated carbon or odor-eliminating filter is the product built for that job. Anyone selling you a particle filter as a fix for gas-phase pollution is overselling it.
It loads it faster. Through a stretch like last week's, a central system can run near-continuously for days, pulling far more air through the same media than a mild week would. A filter that looked fine in mid-August can be meaningfully restricted by early September.
That restriction has a cost beyond air quality. The Department of Energy's building science guidance is direct about it: "A dirty or clogged filter can dramatically reduce airflow, increasing furnace run time, wear on the motor, and energy consumption." During a grid emergency, a restricted filter means your system draws more power to move less air, which is the opposite of what you and your utility both want. Clogged-filter symptoms tend to show up as weak airflow at the registers, longer cycles, and a system that never quite catches up.
Grid strain is not going away. Get your system in shape for the next one.
Late-season heat waves and record demand are becoming a regular feature of the calendar, not an exception. Three moves that make the next one easier on your house:
Sources: Insurance Journal / Reuters, "Blackout Risk Rises as Heat Wave Stresses Largest US Electric Grids," September 3, 2026; US EPA, Ground-level Ozone Basics; US Department of Energy, Building Science Education: HVAC Proper Installation of Filters; US EPA, What is a MERV rating?
