You can have the most efficient furnace and AC ever built, and if your ducts are leaking — and most are — you’re heating the attic and cooling the crawlspace while paying the same monthly bill.
Duct leakage is the most overlooked HVAC issue in Colorado homes, and the easiest to fix once identified.
Why Ducts Leak
Most residential ductwork was installed with cloth tape, which dries out and falls off within 5–10 years. Joints loosen as buildings settle. Mice chew through flex duct insulation. Holes get drilled for plumbing or electrical and never get sealed. Over a 20-year-old system’s lifetime, total leak area easily reaches 10–20 square inches — equivalent to leaving a window open year-round.
What 30% Leakage Costs You
For a typical Colorado home with annual heating and cooling costs:
- 20% leakage = significant annual energy waste
- 30% leakage = even more annual energy waste
Compounded over 10 years, that’s often equivalent to the cost of a new furnace and AC.
Signs Your Ducts Are Leaking
- Some rooms are noticeably hotter or colder than others
- Energy bills creeping up year over year despite no usage change
- Excessive dust on furniture (leaks pull dust from attics/crawlspaces)
- HVAC system runs constantly
- Unusually warm attic in winter or cool attic in summer
- Visible disconnected sections in unconditioned spaces
How We Diagnose Leaks
The gold standard is a duct blaster test: we seal all the registers and pressurize the duct system to 25 Pascals. The flow rate needed to maintain pressure tells us the total leakage. We follow with smoke pencil testing or thermal imaging to find specific leak locations. Most jobs take 2–3 hours and produce a detailed report.
Fixing the Leaks: Three Methods
- Manual sealing — physical access to ducts, mastic sealant on every joint. Best for accessible ductwork. Pricing varies based on access and scope.
- Aerosolized sealant (Aeroseal) — the system is pressurized with a sticky aerosol that finds and seals leaks from the inside. Reaches places no person can. Pricing depends on home size and includes pre/post measurements.
- Replacement — for very old or damaged ducts, sometimes complete replacement is more cost-effective long-term.
Insulation Matters Too
Sealed ducts running through a 130°F attic or 30°F crawlspace still lose energy through conduction. Wrapping ducts in R-8 insulation in unconditioned spaces is just as important as sealing them.
Federal Tax Credits and Xcel Rebates
Through the Inflation Reduction Act, sealing and insulating ducts qualifies for a 30% federal tax credit (check current annual limits with your tax advisor). Xcel Energy in Colorado offers additional rebates for verified duct sealing. Stack them with your contractor and the work often pays for itself within one heating season.