Where ducts go wrong in Chapel Hill houses
Many homes in Chapel Hill run ductwork through a vented crawlspace or a hot attic. Flexible duct in a crawlspace sags off its straps over time, and animals sometimes tear it open. Attic air in summer can pass 130 degrees, so a disconnected joint up there dumps cooled air into the hottest part of the house. The Department of Energy estimates that a typical house loses 20 to 30 percent of the air moving through its ducts to leaks, holes and poor connections.
Signs of a duct problem
- An upstairs bedroom or bonus room stays 5 or more degrees warmer than the rest of the house
- Weak airflow from some vents while others blow hard
- A musty smell when the system starts, often from a damp crawlspace
- Dust that comes back within days of cleaning
- Sweating ducts or wet insulation in the crawlspace in summer
What the fix looks like
The technician will inspect the ducts, and many run a leakage test with a fan that pressurizes the system and measures how much air escapes. Repairs range from resealing joints with mastic and rehanging fallen runs to replacing a crawlspace system. For a single room that duct work cannot fix, a ductless mini-split often costs less than rebuilding the ducts.
About duct cleaning
The EPA does not recommend cleaning ducts on a routine schedule. Cleaning makes sense after a renovation that put drywall dust in the system, when there is visible mold inside the ducts, or after rodents have been in them. For ordinary dust, a better filter does more. Be careful with $99 whole-house duct cleaning offers, which are a common opening for a much larger upsell.
Typical costs
| Job | Typical price |
|---|---|
| Duct inspection and leakage test | $150 to $400 |
| Sealing and repairs | $500 to $2,500 |
| Whole-house duct cleaning | $400 to $1,000 |
| Crawlspace duct replacement | $2,500 to $7,000 |
Questions
Why is my upstairs so hot?
In a two-story house with one system, heat rises, and the ducts to the second floor are the longest and hottest runs. Fixes include balancing dampers, sealing attic ducts, adding a return, or a separate zone or mini-split for the upstairs.
Will sealing ducts lower my bill?
If the ducts leak into an attic or crawlspace, yes. The Department of Energy puts duct losses in a typical house at 20 to 30 percent of airflow, and sealing recovers much of that.