Imagine if you had no control of the amount, quality, location, temperature or timing of the water coming into your house. Imagine if you were to shower, wash your dishes, do your laundry, and cook based on whatever water was hanging around, from whenever it felt like coming through the pipes or the roof or the basement. In this fantasy/nightmare world you also have to deal with the repercussions of unwanted, dirty water coming through your faucet, walls and crawlspace when you weren't prepared for it.
This is how we largely treat the fresh air in our homes.
You want air coming in the same as water, into your house. You want it where you want it, when you want it and clean. Just as you control all aspects of the water coming through your plumbing, you can control the air coming into your house.
After air sealing, there is a minimum safe amount of fresh air needed in your home - largely for breathing and cooking. People used to believe you should build homes super leaky to have ample fresh air. The experts finally saw the folly in that line of thinking and now there is the technology for a much better way. Building Performance Analyst, such as ourselves, can test for the amount of fresh air needed and ensure your home remains safe.
An Energy Recovery Ventilator (ERV) is a piece of equipment that can be installed in your home to mechanically bring in fresh air. The very helpful thing about these, is they exchange the energy of the air going out with the incoming air, so you are not losing your energy dollars. It works with the law of thermodynamics. In the winter time the hot air going out is attracted to the cold air coming in and they exchange temperature. In the summer time the moist air that is coming out is attracted to the dry air going out and loses the humidity. ERVs have 80% efficiency.
With air sealing, building performance testing, and if needed an ERV, you can have clean, conditioned air in your house, when you want it and where you want, it just like the water through your plumbing.
A short video (one minute) in William's own words: