Most Likely Causes (Ranked)
Carbon monoxide is produced by any gas appliance — furnaces, water heaters, stoves, fireplaces. CO becomes dangerous when it can't vent properly: a cracked furnace heat exchanger leaks CO into the supply air, a blocked flue traps exhaust inside, or a downdraft pushes combustion gases back into the house. CO is odorless and colorless — detectors are the only warning.
HVAC duct joints separate from vibration, age, or poor installation. The average home loses 20-30% of conditioned air through duct leaks.
Gaps around pipes, wires, vents, and other penetrations through walls, ceilings, and floors allow air exchange.
House settling creates gaps between framing, foundations, and finish materials that allow air movement.
Missing or compressed insulation allows rapid heat transfer and creates convective air loops.
How to Fix It
Replace Weatherstripping
$5-30- 1Identify worn or missing weatherstripping.
- 2Remove old material, clean surface.
- 3Apply new weatherstripping matched to gap size and type.
- 4Test closure with a dollar bill — should grip firmly.
Seal Duct Joints
$10-30 DIY / $500-2,000 Pro- 1Access ductwork in attic, basement, or crawl space.
- 2Clean joint surfaces and seal with mastic sealant or metal-backed tape (NOT fabric duct tape).
- 3Insulate ducts in unconditioned spaces.
Seal Penetrations
$5-20- 1Identify air leaks with an incense stick or thermal camera.
- 2Seal gaps with appropriate material: caulk for small gaps, expanding foam for larger gaps, backer rod + caulk for big gaps.
- 3Seal around all pipes, wires, and vents passing through floors, walls, and ceilings.
When to Call a Professional
Air leaks increase energy bills by 20-40%.
In cold climates, air leaks cause ice dams and moisture problems.
Duct leaks in attics or crawl spaces can pull in contaminated air.
How to Prevent It
Weatherstrip doors and windows every 3-5 years.
Seal all penetrations during any renovation.
Have ductwork tested and sealed professionally.
Add insulation to recommended R-values for your climate.
Gas Safety: What Every Homeowner Must Know
Natural gas has no smell — the rotten egg odor is mercaptan, an additive specifically so you can detect leaks. If you smell it: leave immediately, no switches, no phones inside, call gas company from outside.
Gas work requires a licensed professional in most jurisdictions. Even tightening a fitting requires proper leak testing and often a permit. DIY gas work is illegal in many areas and genuinely dangerous.
Carbon monoxide (CO) is the invisible killer — odorless, colorless. Install CO detectors on every level. Have gas appliances inspected annually. Replace flex connectors every 10-15 years.
Frequently Asked Questions
15-30% reduction in heating/cooling costs is typical. An average home saves $200-400/year.
Hold a lit incense stick near suspected areas on a windy day. Smoke deflection shows leaks. Professional blower door test ($200-400) finds them all.
No — fabric duct tape fails quickly. Use mastic sealant or UL-listed metal-backed foil tape.
$500-2,000 depending on home size and duct accessibility. Energy savings often recover cost in 2-3 years.