HVAC contractors are booked 6-8 weeks out when smoke hits, leaving no surge capacity
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When wildfire smoke arrives in a metro area like Denver, Salt Lake City, or Spokane, thousands of households simultaneously realize they need MERV-13 filter upgrades, duct sealing, or portable air purifier installation. HVAC contractors in these markets are already at full capacity doing summer cooling work, so the wait time for a filter upgrade jumps to 6-8 weeks — by which point smoke season may be over. Homeowners resort to DIY box-fan-with-MERV-13 'Corsi-Rosenthal boxes' which work but void their furnace filter warranty if installed wrong and do nothing about duct leaks that pull smoky attic air into the home. The structural reason this persists is that HVAC is a licensed trade with a 4-year apprenticeship pipeline, there is no 'surge workforce' equivalent, and the seasonal nature of smoke demand means contractors cannot justify hiring year-round staff for a 4-6 week annual spike.
Evidence
During the 2023 Canadian wildfire smoke event that hit the U.S. Northeast, HVAC companies in New York City reported 300-400% increases in filter-related service calls with lead times extending to 6+ weeks (reported by NY1 News). The EPA promoted Corsi-Rosenthal box fans as a DIY solution but noted they do not address duct leakage, which the Department of Energy estimates causes 20-30% of conditioned air to be lost to unconditioned spaces like attics where smoke infiltrates.