Inversion Season in Utah: What Filters and Duct Cleaning Can and Can't Do

What an inversion is

Utah DEQ explains that in a temperature inversion, cold air at the surface gets trapped under a layer of warmer air. In winter, snow-covered valley floors reflect heat rather than absorb it, which keeps warm and cold air from mixing normally, and the Wasatch and Oquirrh mountains and Traverse Mountain form a basin that holds cold air in the Salt Lake Valley.

DEQ says a typical Utah winter sees about five to six multi-day inversion episodes. Pollutants from vehicles, wood burning, industry, and other sources get trapped near the ground, and PM2.5 concentrations build the longer the inversion lasts.

Source: Utah Department of Environmental Quality — Inversions

Why the furnace matters in Utah homes

According to EIA's 2020 survey, about 90% of Utah homes use a furnace as their main heating equipment — far above the national figure of about 60%. A furnace moves warm air through ducts, so during inversion season most Utah homes are relying on the duct system and its filter.

Sources: U.S. EIA — Highlights for space heating in U.S. homes by state, 2020 (RECS); U.S. EIA — RECS terminology

Duct cleaning isn't an inversion fix

Inversion pollution comes from outdoor air. Cleaning ducts removes dust and debris that has already settled inside them; it doesn't filter the air coming into your home. EPA notes that much of the dirt in ducts sticks to duct surfaces and doesn't necessarily enter the living space, and it says duct cleaning has never been shown to actually prevent health problems.

Source: U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?

The filter does the daily work

EPA recommends the highest-efficiency filter your system's manufacturer recommends, changed regularly. If you're upgrading, EPA suggests at least MERV 13, or as high a rating as your system fan and filter slot can accommodate — higher MERV filters are better at trapping particles, but not every system is built for them. An HVAC technician can tell you what yours can handle.

• Check the filter more often during long inversion stretches and replace it when it's dirty.
• Make sure the filter fits its slot without visible gaps.
• Keep a spare filter of the right size on hand before winter.

Sources: U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?; U.S. EPA — What is a MERV rating?

When duct cleaning does make sense

EPA does not recommend routine duct cleaning. It suggests considering cleaning when ducts are clogged with excessive dust and debris or particles come out of supply registers, when ducts are infested with vermin, or when there is substantial visible mold growth inside hard-surface ducts. We clean ducts, registers, and grilles; we don't diagnose or remediate mold or apply chemical treatments.

Leaks are a separate issue. ENERGY STAR estimates that a typical duct system loses about 20 to 30 percent of its air to leaks and poor connections, and that dust can get into leaky ducts. If ducts in an unfinished basement or crawlspace are disconnected or leaking, sealing is the fix — a job for an HVAC contractor.

Sources: U.S. EPA — Should You Have the Air Ducts in Your Home Cleaned?; ENERGY STAR — Duct Sealing; ENERGY STAR — Benefits of Duct Sealing