It doesn't matter how high in the sky a home is, good air quality still matters to luxury homeowners.

This listing of a three-story penthouse in New York City's Upper West Side has an 18-zone air purification system built into the central Carrier HVAC system, according to Louise Phillips Forbes, a broker with Halstead Property.

The filtration system includes a UV light, and energy-efficient fans run to keep the air purified. There is also a centralized humidification system for use in the winter.

Forman added that water purification has also been a big focus among some clients. "It's not just at the tap, they are purifying the water at the source of it coming into the home. It might go through four different purification systems before it hits the plumbing."