This ongoing series is all about the smart home, looking at smart technology that's going to change the way we live. Most are high-tech and complex, but this one is so simple and logical — it's surprising it hasn’t been done before.

Most people who live in apartments or condominiums are not aware of the source of their air. In most buildings it is coming from the hall, through the undercut at the bottom of the door. This “corridor ventilation strategy” is designed this way by mechanical engineers; corridors are pressurized with air pumped down from the roof so that cooking and tobacco smells don't spread throughout the floor. This often-unfiltered outside air then flows through the dirty hall carpet at your threshold and into your apartment, and it can contain dust, dander, allergens and animal droppings. Yuck.

typical corridor and air flow in an apartment building

How most apartments get their air. (Photo: Door Filter)

That’s why this new Door Filter is so clever.

Door Filter is a dense ABS extension that is fitted and secured to the bottom of the inside face of an apartment entry door and lined with a door sweep (to seal off units). A removable multi-stage air filter (charcoal, particulate and microbe) is placed inside the device. Small openings in the ABS allow air to pass through the device and internal filter promoting clean airflow into the apartment unit. 
door-filter closeup

The door filter keeps the crap outside. (Photo:Door Filter)

It covers that gap at the bottom of the door with a filter designed to “strike a balance between ensuring maximum air flow while capturing the majority of particulate that would otherwise flow into your home.” You can’t seal off the gap completely or you'll mess up your ventilation, and you might get smells coming back through your bathroom and kitchen exhaust. But you can ensure that the air coming in is not carrying bacteria and dust mites and other gunk hanging out in the carpet or being pumped in from the outside.

There are alternative systems for apartments, with separate suite-by-suite ventilation, but that's an expensive option so developers and builders don’t install them. It's unfortunate that so many buildings rely on such a cheap and awful way of supplying air. It really is the dirty little secret of apartment building design. At least the Door Filter provides a bit of protection. This is a smart idea.

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Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Cleaner apartment air is a Door Filter away
Most apartments get "fresh" air through the gap under the entrance door. The Door Filter cleans it before it gets in.