- It can be pretty simple. It doesn't take million dollar, multi-million dollar fixes and you can do this if you have operable windows, opening up the window, even a couple inches. Depending on the airflow, the weather conditions outdoors, you can get two, four, six, or even 12 air changes per hour. We also like supplementing that with portable air cleaners with HEPA filters, not so dependent on the weather conditions, or if you have a mechanical ventilation system, bringing in more outdoor air. Again, I wanna take this back to say there's always something you can do. If you have an old building with a rundown mechanical system, you can use these low cost, portable air cleaners as a simple strategy. You have windows that don't open, you can do the same thing, but ideally, right? If we have operable windows, you open them up, even a couple inches. You can put a fan in that window to facilitate the transfer of air. And so, the strategies I haven't been recommending, advanced air cleaning technologies for schools, it can actually be done simply and very cost-effectively.