Is it safe to use an extension cord permanently for a window AC unit in older homes?

Short answer

Why people ask this

People in older homes often lack a nearby grounded outlet for a window AC or have short factory cords that don’t reach. They may also be dealing with two‑prong receptacles, worn outlets, or shared circuits and hope an extension cord is a quick fix. Window ACs draw high current for compressors and fans, which stresses cords and old receptacles. In older wiring systems (like knob‑and‑tube or aluminum branch circuits), added resistance from a cord increases heat and voltage drop. Homeowners also worry about tripping breakers, nuisance shutdowns, or voiding insurance.

When it might be safe

There are no commonly accepted situations where this is considered safe.

When it is not safe

• Window ACs commonly draw 8–15A; many extension cords aren’t rated for continuous heavy load, causing cord and plug overheating.
• Voltage drop from long or light‑gauge cords makes compressors hard‑start, overheat, and cycle poorly, especially on older circuits.
• Older homes may have two‑prong or worn receptacles; using adapters or loose outlets defeats grounding and creates hot plug connections.
• Aging wiring (knob‑and‑tube, aluminum, mixed splices) plus an added cord’s resistance increases heat under rugs, coils, or behind furniture.
• Electrical codes treat extension cords as temporary only; using one as permanent wiring can violate code and insurance requirements.

Possible risks

• Overheating at the cord, plug, or old receptacle leading to scorch damage or fire.
• Compressor damage from brownouts and repeated hard starts due to voltage drop.
• Shock risk from ungrounded two‑prong adapters or damaged cord jackets.
• Nuisance breaker trips on shared, older circuits (lights dimming, TV resets).
• Insurance claim disputes if fire investigators find a permanently used extension cord.

Safer alternatives

• Have an electrician install a dedicated 15A or 20A grounded receptacle within reach of the AC using proper 14/2 or 12/2 wiring and a matching breaker.
• Assess and update older wiring: replace worn two‑prong outlets with properly grounded receptacles, repair loose connections, and add AFCI/GFCI as required.
• Select an inverter/efficient lower‑amp window unit or a mini‑split; both reduce starting current and are better for older circuits when properly installed.
• Run a new dedicated circuit from the panel to the window location; avoid shared lighting or kitchen circuits common in older homes.
• If a stopgap is unavoidable, use only a short (6 ft or less), heavy‑gauge (12 AWG), single‑outlet appliance cord rated 15A/125V, kept flat and uncovered—then replace with a dedicated outlet promptly.

Bottom line

For a window AC in an older home, a permanent extension cord is not safe. Install a properly grounded, dedicated outlet or circuit and address any aging wiring so the unit runs reliably without overheating cords or receptacles.

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