When replacing the outdoor unit, should the indoor unit also be replaced? At Hillcrest Air Conditioning & Plumbing, we do recommend replacing both your indoor and outdoor units at the same time because: Outdoor systems are now built to work with their matching indoor system for the most efficiency. When you replace one system but not the other, you may not see the same energy savings as if you had replaced them together. Thanks to technological improvements, newer systems mean improved efficiency. This is true for heating and cooling products as well. While the advancements focus on improved heating and cooling efficiency, they also include benefits such as better air handling, filtering and noise reduction. If your heating and cooling systems are more than 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 Older models have outdated technology that is likely adding to your energy costs due to poor efficiency.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 decrease your energy bills and keep your home more comfortable.