Inspection and Free Estimate. Typical services completed by HVAC companies focus on inspection. Your HVAC system is surveyed as well as the space to which it will provide ventilation. This applies to each kind of HVAC. When you have a centralized HVAC system, it might take more time for your contractors to produce a full estimate. You will find HVAC contractors that do free estimates. Select one that offers this package so you can save.