When people think of HVAC, they usually imagine cooling, heating, or comfort. But beyond temperature control, one of the most critical—and often overlooked—factors in healthy buildings is indoor air pressure balance. The right pressure ensures that air flows in the right direction, protecting people, enhancing comfort, and improving safety.

What is Indoor Air Pressure?

Indoor air pressure is the result of balancing three components of an HVAC system: Treated Fresh Air (TFA), Extract Air, and Recirculated Supply Air.
• When Supply Air > Extract Air, the space is under Positive Pressure.
• When Extract Air > Supply Air, the space is under Negative Pressure.
• When both are balanced, the space is in Neutral Pressure.

This balance decides whether a room pushes air out, pulls air in, or stays stable.

Positive Pressure

Positive pressure means more air is supplied than exhausted. This forces clean air out of the space whenever doors or openings are accessed, preventing contaminants from entering.

Applications:
• Hospitals: Operating rooms, ICUs, clean rooms
• Homes: Living rooms, bedrooms
• Restaurants: Dining areas
• Offices: Lobbies and workspaces

Benefit: Protects occupants by keeping contaminants, dust, and odors out.

Negative Pressure

Negative pressure means more air is exhausted than supplied. This creates a suction effect, pulling surrounding air into the space. It is used to contain pollutants, odors, or infections within a defined area.

Applications:
• Hospitals: Isolation rooms
• Homes: Kitchens and toilets
• Restaurants: Kitchens
• Industries: Paint booths, labs, and chemical areas

Benefit: Prevents spread of odors, smoke, or infectious agents into cleaner areas.

Neutral Pressure

Some spaces don’t need positive or negative dominance. Neutral pressure is used in comfort-driven environments like classrooms, open-plan offices, or general retail areas, where stable air balance is sufficient.

Everyday Examples
• In Homes: Living rooms stay positive to remain fresh, while kitchens and toilets stay negative to stop odors and smoke from spreading.
• In Restaurants: Dining halls are positive for guest comfort, kitchens are negative to keep cooking fumes contained.
• In Hospitals: Operating theaters are positive to protect patients, while isolation wards are negative to contain infections.

MOLTEN’s Commitment

At MOLTEN, we recognize that air pressure is not just about engineering—it’s about Creating Healthy Environments. Our HVAC designs and commissioning services are built to ensure the correct pressure balance for every project, whether it’s a home, hospital, restaurant, or industrial site.

By combining technical expertise, sustainable design, and global standards, we deliver environments that are safer, cleaner, and healthier—today and for the future.

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