O'Fallon is a moderate cost-of-living market — pricing guide and permit rules below.
O'Fallon hvac rates: $3,000-$10,000 per system. O'Fallon's freeze-thaw cycles stress systems. Always get 3 written quotes and verify MO licensing at Missouri DPR (pr.mo.gov). Sales tax on materials: 8.5%.
O'Fallon requires permits when work exceeds $10,000 or involves full system replacement. Your licensed contractor pulls the permit — if they ask you to pull it, that's a red flag.