Why an oversized furnace short-cycles

An oversized furnace heats fast, overshoots, and shuts off in short bursts — swings and wear. A right-sized furnace runs longer, steadier cycles. Manual S caps it near 140% of the load.

Two room-temperature-over-time timelines. The oversized furnace on top swings sharply above and below the target temperature in many short bursts. The right-sized furnace below holds a gentle, steady line near the target with longer cycles. Short-cycling causes drafts, uneven rooms, and extra wear. — Source: ACCA Manual S

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Two room-temperature-over-time timelines. The oversized furnace on top swings sharply above and below the target temperature in many short bursts. The right-sized furnace below holds a gentle, steady line near the target with longer cycles. Short-cycling causes drafts, uneven rooms, and extra wear.

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