How to choose home fresh air system?

Noise conditions. Not to mention the noise as low as 20 decibels. The so-called sleep gear is the minimum air volume, the fans are almost stopped, and the air volume is pitifully small. What's the point of such low noise? Don't be entangled in the words of the manufacturer. Look directly at the noise of the top-grade and ordinary gears suitable for your area. If the noise goes against the sky at the highest level and is basically useless, it is meaningless. The noise of common gears is the most critical. This gear can meet the demand of indoor fresh air, and the noise must be within an acceptable range.