Can I use a heat pump with my existing ductwork?

Usually yes — after a test

The ductwork question is the real one in this city. 57.1% of Casselberry’s 8,563 improved residential parcels were built between 1970 and 1989, the median build year is 1977, and in that stock the equipment has been replaced three or four times while the attic trunk very often has not.

What has to be true for your existing ducts to work with a heat pump:

• Enough return. The single most common defect in 1970s Florida tract housing is one undersized central return sized for the original equipment. A heat pump with a variable-speed blower wants more air than that return can pass.
• External static pressure within the equipment’s rating. A measured number in inches of water column, taken before and planned for after. If the system cannot move its rated airflow it will not deliver its rated capacity or its rated SEER2.
• Acceptable leakage. Supply leakage into a 130°F vented attic is lost money; return leakage pulls that same hot, humid attic air into the house, which in this climate is a humidity problem as much as an efficiency one.
• Insulation that is still there. Flex duct from the 1970s and 80s has often had four decades of attic heat and rodents.

The rebate that pays for the test

Duke Energy will pay for a large part of finding out. The duct test and repair rebate covers 50% of the cost of the duct test plus up to $200 toward repairs, per system, single-family only — after the free Home Energy Check. That is the cheapest way to answer this question properly, and it happens to be a prerequisite for the heat pump rebate you would also be claiming.

If the ducts do need work, the Florida cost guide puts duct repairs or replacement at $1,500–$5,000 on top of the equipment. That is a real number and it is better to know it before you choose the equipment than after. Duct costs in Casselberry.

Heat pumps do not need bigger ducts. They need honest ones.

One thing worth separating out. People sometimes ask this question because they have been told a heat pump needs “bigger ducts.” That is not quite it. A heat pump and an air conditioner are the same machine in cooling mode and move the same air. The difference shows up in heating: a heat pump delivers a lower supply temperature than strip heat does, for longer, so airflow matters more and marginal duct work that survived thirty summers can announce itself in January. What a conversion actually changes.

Seminole County Property Appraiser CAMA extract (Parcels.csv, dated 2026-09-05). Improved residential parcels — single-family, townhome and condominium — in city tax district C1, City of Casselberry. n = 8,563.