Everything we have on hvac — what fails, why, what it costs, and which of it you can handle without calling anyone.

Homes built before about 1940

Pre-war construction — galvanized supply, cast iron drains, cloth-wrapped wiring, ungrounded circuits.

• Ductwork threaded through a house built for floor grates
• One central return for the whole house
• Water heater vents into the chimney and the furnace no longer does
• Silver-wrapped tape on old duct joints
• Additions still on window units
• Uninsulated walls and an oversized condenser
• Furnace runs but the house never warms evenly
• Electrical panel cannot support a modern condenser
• Filter slot is a gap behind a grille

Homes built roughly 1940 to 1980

Post-war and mid-century — copper supply, aging cast iron stacks, 60 to 100 amp panels, first-generation central air.

• R-22 system leaking refrigerant
• Rust or soot streaks at the furnace heat exchanger
• Ducts in an unconditioned attic
• Thermostat has only four wires
• Condenser pad has sunk and the unit leans
• System cools but the house stays humid
• Evaporator coil freezing over
• Only some rooms cool, and always the same ones
• Blower runs constantly and never satisfies

Homes built roughly 1980 to 2000

The polybutylene and aluminum-wiring window, 150 amp panels, R-22 systems and first-cycle architectural shingle.

• SEER 10 system still running at thirty years
• Flex duct crushed or kinked in the attic
• Water on the floor near the air handler
• Cooling drops off on the hottest days only
• One zone stuck hot or cold
• Squeal or grind from the air handler
• Refrigerant line insulation crumbling
• Outdoor unit caked in cottonwood and red dust
• Thermostat set to 72 and the house reads 78

Homes built since 2000

PEX on slab, 200 amp service, builder-grade equipment that reaches end of life across a whole street at once.

• Whole street replacing systems the same year
• Upstairs runs hot no matter the setting
• Control board fault on a communicating system
• Smart thermostat installed and the heat now runs oddly
• Condensate pump buzzing or backing up
• White PVC vent pipes outside stained or dripping
• House feels stuffy in a new build
• Fifteen degree difference between floors
• Loud startup thump from the outdoor unit

Any age of home

• Furnace ignites, runs a minute, shuts off
• Gas smell near the furnace
• Heat pump runs constantly below freezing
• Outdoor unit steaming in winter
• Dual fuel system switching at the wrong temperature

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Written by Jaylan Jones. I Like To Fix earns a referral fee when a call connects to a contractor. See our business-model disclosure.