The answer to 'how much does replacement cost' is that the cost of an HVAC system replacement can vary significantly depending on several factors. In general, you can expect to pay anywhere from $3,000 to $15,000 or more for a full HVAC system replacement, including the unit, installation, and any necessary ductwork or electrical work.
The exact cost will depend on the size of your home, the efficiency rating of the new system, the brand and model you choose, the complexity of the installation, and your local labor and material costs. It's important to get quotes from multiple local HVAC contractors to find the best price for your specific needs.