When replacing the outdoor unit, should the indoor unit also be replaced? At Dial One Mears Air Conditioning & Heating Inc, we do recommend replacing both your indoor and outdoor units at the same time because: Today, outdoor systems are built to work with their matching indoor system for maximum efficiency. When you replace just one of your systems, you may not see the same energy savings as if you had replaced them together. Thanks to technological improvements, newer systems mean increased efficiency. This is also true for HVAC systems. While the advancements focus on higher heating and cooling efficiency, they also include benefits such as better air handling, filtering and noise reduction. If your heating and cooling systems are 10+ years old, they need to be replaced. Older models have outdated technology that is likely adding to your energy costs due to poor efficiency. So by replacing your indoor system at the same time as your outdoor equipment, both your systems will provide better energy efficiency that helps you lower your energy bills and keep your home more comfortable.