You may be interested in heat-recovery ventilation (recuperation). For example, you can buy this one from Ukraine: https://prana.ua/en/products/prana150ee/ (not affiliated with them, just bough one similar unit for my own house).
Cool! I never heard of this, so I had to look it up:
Heat recovery ventilation, also known as HRV or mechanical ventilation heat recovery (MVHR), is a system that works by transferring heat from outgoing exhaust air to incoming fresh air. Here's a simple step-by-step process:
1. Stale air from the inside of a building is expelled through the system.
2. As the stale, warm air leaves, it passes over a heat exchanger.
3. Fresh, cool air from the outside is drawn into the system, passing over the same heat exchanger.
4. The heat from the outgoing air is transferred to the incoming air without the two air streams mixing.
5. The pre-warmed fresh air is then distributed throughout the building.
This process ensures a constant, controlled supply of fresh air, maintains indoor air quality, and conserves energy that would otherwise be lost in the ventilation process.
