HVAC problems found during a home inspection
Gas, flue and heat exchanger findings come first among heating and cooling items on a home inspection. Replacements and tank cleanup cost the most.
Updated · By 
Ben Sikes
What heating and cooling problems are found during a home inspection?
This list covers 15 heating and cooling findings an inspection can flag, what a primary source says about each, and what each costs. The safety rows are the ones that can put carbon monoxide (CO) in the house: a cracked heat exchanger, a backdrafting or rusted flue, insufficient combustion air, a floor or gravity furnace, and an unvented gas space heater. Get a licensed pro's written bid on those before your deadline. The big money is in replacing a furnace, boiler or AC unit, and in an underground oil tank that has leaked.
Key takeaways
- Ask for a combustion safety test whenever a duct bid seals anything on a gas or oil system.
- Chimney rows go to a certified chimney sweep, not an HVAC contractor.
- Get the age of the furnace, boiler and AC unit off the data plates before you price any of them.
| Finding | What the source says | Cost to fix | Who prices it | Guide |
|---|---|---|---|---|
| Asbestos duct wrap | Environmental Protection Agency (EPA): if it is more than slightly damaged, "repair or removal by a trained and accredited asbestos professional is needed" | $2 to $6 per sq ft to seal in place; worst case: $35 to $55 per sq ft to remove (Bob Vila, Fixr, national) | Asbestos abatement contractor | Guide |
| Backdrafting or rusted flue | EPA: "CO can kill you before you are aware it is in your home" | $100 to $350 for a water heater flue pipe (HomeLintel, national); worst case: $4,800 for an emergency chimney liner on one client's new water heater (Better Water Heaters, local, Bay Area) | Licensed plumber or HVAC technician | Guide |
| Chimney cap, damper and creosote | Chimney Safety Institute of America (CSIA): "whatever form it takes, creosote is highly combustible" | $325 to $485 for a galvanized steel cap installed (Bob Vila, national); worst case: $1,000 for a wood-burning fireplace sweep (Bob Vila, national) | Certified chimney sweep | Guide |
| Clogged condensate drain line | Carrier: "do not risk water damage to your home" | $75 to $250 to clear and flush the line (J Martin, local, Orange County, CA); worst case: $5,000 or more for mold remediation (J Martin Indoor Air Quality, local, Orange County, CA) | HVAC technician | Guide |
| Cracked heat exchanger | Lennox: "Cracks can leak carbon monoxide, reduce efficiency, and strain other components" | $1,000 to $3,000 to replace the heat exchanger (Trane, national); worst case: $12,000 for a new gas furnace (Plumb-Line Services, local, Denver) | Licensed HVAC technician | Guide |
| Ductwork findings | ENERGY STAR: leaky ducts "may cause 'backdrafting,' where these gases are drawn back into the living space" | $100 to $500 for a loose section (Fixr, national); worst case: $12,000 or more to replace old ductwork (Cunningham Oil, national) | HVAC contractor | Guide |
| Floor or gravity furnace | International Association of Certified Home Inspectors (InterNACHI): "carbon monoxide in the supply air, which can result from openings in the seams of the burner chamber" | $3,800 to $10,000 for a new gas furnace installed (HomeAdvisor, national); worst case: $15,000 for a mini-split in place of a furnace (HomeAdvisor) | Licensed HVAC contractor | Guide |
| Insufficient combustion air | InterNACHI: "CO spillage may occur" from an insufficient supply of combustion air | Get a written bid; the contractor's quote sets it after measuring the room and checking each appliance's rating | Licensed HVAC contractor | Guide |
| Old AC unit or R-22 | EPA: "There is no EPA requirement to get a new system or convert existing HCFC-22 units" | $90 to $250 per pound of R-22 (Trane, national); worst case: $15,000 for a central AC replacement (Carrier, national) | Licensed HVAC technician | Guide |
| Old boiler | InterNACHI: natural draft boilers "rely entirely on a high flue temperature relative to the outside temperature to draw exhaust gases up and out of the flue" | $4,290 to $10,070 (Carrier); $4,500 to $10,000 (This Old House) | Licensed heating contractor | Guide |
| Old furnace | EPA lists "worn or poorly adjusted and maintained combustion devices (e.g., boilers, furnaces)" as a CO source | $3,800 to $10,000 to replace with a gas furnace; $6,750 to $10,000 for oil (This Old House, national) | Licensed HVAC technician | Guide |
| Underground oil tank | InterNACHI: a buried tank "may pose a safety hazard to those living in homes nearby and significant financial liability to the owner" | $300 to $700 for an inspection (Eastern Environmental, local, Long Island, NY); worst case: $50,000 to $250,000 for cleanup once oil reaches groundwater (UST Contractors, California directory) | Tank-testing contractor | Guide |
| Unlined chimney | CSIA: a chimney fire burns at "around 2000°F" and can "melt mortar, crack tiles, cause liners to collapse" | $1,800 to $4,000 for a stainless steel liner installed; worst case: $7,000 for a cast-in-place liner (Fixr, national) | Certified chimney sweep | Guide |
| Unvented gas space heater | Bluegrass Living manual: "Carbon monoxide poisoning may lead to death" | $400 to $2,000 for a vented wall unit (CostHelper, national); worst case: $10,000 for a gas furnace installed (HomeAdvisor, national) | Licensed HVAC technician | Guide |
| Wood stove clearance to combustibles | Purdue Extension: with no wall protection, the common radiant stove "must be spaced out at least 36 inches from the wall" | $150 to $400 for a listed wall shield panel, panel only (Wood Stove Hub) | Certified chimney sweep or stove installer | Guide |
Kept prices every line of an inspection report for $79, usually under 4 hours, and marks the ones that need a professional quote, like a furnace replacement or a buried oil tank.
What is the biggest red flag in a heating and cooling inspection?
No single row is the worst on every report. The red flags are the rows where the source describes harm to people, which is every CO row in the table. Treat a cracked heat exchanger, a backdrafting flue and an unvented gas heater as a reason to book the technician the day you read the report.
Two situations are emergencies, not price lines. If a CO alarm sounds or anyone feels sick, the Consumer Product Safety Commission (CPSC) says to "get outside to fresh air immediately, and then call 911." If you smell gas, American Standard says to "leave your home immediately and call the gas company." Then have a licensed professional check the system before anyone runs it again.
What is the $5,000 HVAC rule?
Carrier says to multiply the age of your system by the estimated repair cost. If the result exceeds $5,000, replacement is generally more cost-effective to consider. Carrier calls it a rule of thumb, not a substitute for a professional evaluation. The old AC unit guide works it through for a 15-year-old unit. A written bid prices the decision.
Does a home inspector check the furnace and heat exchanger?
Partly. Under InterNACHI's Standards of Practice, an inspector is "not required to: inspect, measure, or evaluate the interior of flues or chimneys, fire chambers, heat exchangers." A cracked heat exchanger or a flue problem can therefore come from a technician's visit instead of the report. The cracked heat exchanger guide covers what to ask the technician to put in writing.
How to use this list before your deadline
- Match each heating and cooling line on your report to a row above.
- Book the trade in the Who prices it column for the CO rows and any chimney row, and ask for a written bid by line.
- If a duct bid seals leaks, ENERGY STAR says the contractor should make sure there is no backdrafting of gas or oil appliances and run a combustion safety test after the ducts are sealed. Ask for that test in the bid.
- Ask for a repair, a credit or a price cut backed by those numbers. If the seller repairs, ask for the contractor's paid invoice before closing.
- If the seller says no, your contract sets your options and dates. Confirm both with your agent or attorney.
While the technician writes the bid, upload your inspection report to Kept and have the rest of your list priced.
Sources
- Bluegrass Living, Gas Space Heater Manual
- Bob Vila, Asbestos Removal Cost
- Bob Vila, Chimney Cap Cost
- Bob Vila, Chimney Sweep Cost
- Better Water Heaters, Water Heater Backdrafting
- Carrier, AC Drain Line Cleaning
- Carrier, Boiler Replacement Cost
- Carrier, HVAC Replacement
- CPSC, Carbon Monoxide Information Center
- CSIA, Preventing Chimney Fires
- Cunningham Oil, HVAC Ductwork Cost
- Eastern Environmental, Oil Tank Inspection on Long Island
- ENERGY STAR, Hire a Professional Duct Contractor
- ENERGY STAR, Duct Sealing Benefits
- EPA, Protect Your Family From Exposures to Asbestos
- EPA, Carbon Monoxide's Impact on Indoor Air Quality
- EPA, Purchasing and Repairing Home Air Conditioners or Heat Pumps
- Fixr, Asbestos Removal Cost
- Fixr, Chimney Liner Installation Cost
- Fixr, Ductwork Repair Cost
- HomeAdvisor, Furnace Installation Cost
- HomeLintel, Water Heater Flue Pipe Replacement Cost
- InterNACHI, Gravity Furnace Inspection
- InterNACHI, Spill Switch Inspection
- InterNACHI, Inspecting Gas-Fired Boilers
- InterNACHI, Underground Fuel Storage Tank Hazards
- InterNACHI, Residential Standards of Practice
- J Martin Indoor Air Quality, Clogged AC Condensate Drain
- Lennox, Cracked Heat Exchanger
- Plumb-Line Services, Replace a Heat Exchanger or Buy a New Furnace
- Purdue Extension, Wood Stove Clearances
- This Old House, Boiler Replacement Cost
- This Old House, Furnace Cost
- Trane, Cracked Heat Exchanger
- Trane, Is R-22 Refrigerant Still Available
- UST Contractors, Tank Inspection Testing California
- Wood Stove Hub, Wood Stove Heat Shield
- American Standard, When to Replace a Furnace
- CostHelper, Furnace Cost
Cost figures are modeled from public wage and materials data unless a line says observed. Kept is accountable for the numbers on this page, and corrections go to support@usekept.com. How we price.