Oversized Furnace Not Detrimental to Efficiency

Oversizing or undersizing the air conditioning systems is critical, but there is no evidence that an oversize furnace is detrimental to efficiency. Further, oversizing a furnace can compensate for duct design and installation issues. Of course, that’s not a good reason to settle for sloppy workmanship and oversizing furnaces.

Heating systems use lower air flow than cooling systems.  Many times furnaces are oversized to provide additional air flow for the cooling system.

The take away is that it is not worth the investment to replace an oversized furnace in an existing home.