Gravity systems moved air with no fan and no ducts worth the name. When central air went in decades later the ducts were run wherever they fit – crawlspaces, closets, dropped soffits. Static pressure is usually the real problem, not the equipment, and replacing a condenser without fixing the duct does nothing.

This is most common in homes built before about 1940. Pre-war construction — galvanized supply, cast iron drains, cloth-wrapped wiring, ungrounded circuits.

Related

• 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

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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.