You will most likely need a permit to replace your HVAC system. Check with your local building department to find out the requirements in your area. They may require that you submit plans for the new system, or they may have specific requirements for the installation. Either way, getting the proper permits before starting any work is essential. Failing to do so could result in a fine or even having to tear down the new system. So, save yourself the hassle and make sure you get the proper permits before starting any work on your HVAC replacement project.