Here is how to make it: Purchase a standard 20″ Box Fan. Mine cost $20 at a local home improvement store. Apply gasketing to the edges of the air intake part of the fan. Securely fasten a MERV 13 filter to the air intake side of the fan. The air flow arrow on the filter needs to be pointing to the fan. You can tape the filter to the fan. I used large rubber bands. Turn on. Total cost – less than $50.
One thing we need to make clear – this device is not a HEPA air purifier. It does not have a Clean Air Delivery Rate (CADR) which is the standard for measuring the effectiveness of air cleaners. Purchasing and using a HEPA air purifier is the better option. However, their cost may be prohibitive. In this case the “Box Fan with a MERV 13” filter is a reasonable option.
By using a 4″ MERV 13 filter instead of a 1″ filter, resistance is cut down and the flow rate increases from 320 fpm to 460 fpm. Increased media area also means longer filter life. So a good option to increase the performance and preserve the motor of the “Box Fan with a MERV 13″ air cleaner is to go to a 4” filter.
at least 4 feet away from all walls – the closer to the center of the room the better. You should position it so as much of the indoor air passes through the filter as possible
Another option is to place it in an open window – facing in.
But there are some advantages of placing the fan in the window. You substantially increase the amount of ventilation air coming into the indoor space. Proper ventilation is one of the keys to making buildings safer from the transmission of Covid-19. The “Box Fan with the MERV 13” can filter the air before it enters the space thereby reducing allergens and other pollutants found in outdoor air. The fan in the window also positively pressurizes the indoor space so that contaminants are pushed out – preferably through another window.
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