Match CFM, tonnage, and coil capacity to the actual system—so there's no airflow noise, no coil freeze, and no warranty argument with the manufacturer.
Too little airflow over the evaporator coil causes freeze-ups. Too much causes incomplete dehumidification and moisture problems. The standard is 400 CFM per ton of cooling—but leaky ducts, high ceilings, and poor envelope can push that requirement up or require derating. Get it wrong and you own the callback.
The air handler must match the condensing unit or heat pump within a half-ton. Mismatched tonnage voids most manufacturer warranties. When replacing just the air handler, always verify the outdoor unit's rating plate before ordering—age-related derating means a labeled "3-ton" outdoor unit may be performing at 2.5.
If you test duct leakage at 20%, the effective delivered capacity is 20% lower. You can either seal the ducts first (recommend this) or upsize the air handler slightly to compensate—but upsizing without sealing creates an oversized system that short-cycles. Document your reasoning when you deviate from calculated tonnage.
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Get the HVAC Kit →An improperly sized air handler causes comfort complaints, high energy bills, and equipment failures. This calculator determines the correct air handler CFM rating based on square footage, load calculation results, and duct system capacity. Use it to size replacements correctly and avoid the callbacks that come from swapping in the same size as the old unit without checking.