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How does that work? Is it just a setting on industrial HVAC systems or did it require someone coming out and reconfiguring things? I’ve heard some schools are considering leaving the windows open year-round while running the heat/AC to get air turnover. Maybe because those HVAC systems are dated?

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Most big HVAC systems have this ability. On a rooftop unit usually it's as simple as a hatch that you slide; a split system would have to have a separate fresh air duct you can control with a damper. Newer systems typically have explicit fresh air makeup systems with heat exchangers.

Most schools with forced air ventilation should already have such a capability, if they bothered to look. If not, if would certainly be cheaper to have one installed than to leave the windows open. But of course, it may be easier to do one than the other bureaucratically.

> Most big HVAC systems have this ability.

This is patently untrue.

It's an industrial HVAC system that has control systems to allow this (simply just changing damper settings)...but ours is also ~25 years old. Schools opening windows would just be a low tech way of looking at how we change the damper settings.

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