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    BTU Heating Calculator — Furnace & Boiler Sizing

    Is bigger always better for furnace sizing?

    No — oversizing causes short cycling, uneven temperatures, and lower efficiency. Manual J recommends sizing within 100–115% of the calculated design load. A right-sized two-stage or modulating furnace will outperform an oversized single-stage every time.

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    Related questions

    Estimates and general guidance only. Verify against your local code and AHJ before any installation. Gas, electrical, and refrigerant work is hazardous to untrained users.

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