Another factor to consider when replacing your furnace and AC is your overall installation cost. While you would have to pay more up front, replacing both units at the same time could save you money on your installation costs in the long run. When an installer combines two tasks into one appointment, they can usually merge some of the expenses. So, for example, you may only have to pay flat-rate charges for items like mileage and building permits one time instead of twice. Having the heating and cooling systems installed together can also save you on labor costs. To illustrate, let’s say installing a complete system would take six hours while installing two units at different times would take four hours apiece. Since labor is billed by the hour, you would pay for two fewer labor hours by installing them simultaneously.