In many cases, general contractors have certain areas of expertise and do hands-on work. They also know when to delegate tasks to specialized professionals. It can take the average technician between eight hours and an entire day to replace an HVAC system. Depending on the location and accessibility of the home as well as the HVAC contractor’s expertise, this time frame may increase to a couple of days or even a week when a new system needs to be installed. In the Chicago area, there are 3,583 households that have air conditioning systems installed.