Energy saving of a controlled residential ventilation system is not really the decisive point. The controlled residential ventilation system also requires electricity and the approximately 90% efficiency... well, paper is patient, it is rather the gain in comfort that counts with a controlled residential ventilation system. In other words, you will probably never recoup the costs of a controlled residential ventilation system through energy savings! But always fresh air, no cold drafts, and no fogged-up windows could be worth it.