An air conditioner replacement contractor needs to properly size everything. Including air-ducts. If they are installing brand-new HVAC system, always check the duct work. Qualified professionals use the ACCA manual D to appropriately sized ductwork. Having uninsulated ducts or leaky ducts can reduce the overall system efficiency. So it is very important to find the right professional for this task.
If you have a new construction project it’s always best to stick with a qualified HVAC contractor. Because you could end up with an air conditioner that’s very expensive to run. Expensive and not very effective. All joints and seams need to be sealed off in your ductwork. This needs to be addressed before any new HVAC system is installed. If your ductwork remains not insulated or the joints and seams are not sealed off with duct tape. You can experience massive losses in cooling or heat.
It’s important to remember that if your home doesn’t have the right ducts, the cost of installation could potentially get quite expensive. If you do not plan on cooling your entire home you could also consider using a split ductless system. One that offers no ductwork and high-efficiency electrical connection. These systems are much easier to add into homes. However some central air units do only cool certain rooms.