How Positive & Negative Pressure Machines Are Used in Healthcare

In health care environments, i.e., hospitals, clinics, and laboratories, air quality is crucial for safety. Positive and negative pressure systems are among the most useful infection control measures available. These systems work silently to safeguard patients and healthcare workers every day from dangerous airborne contaminants.

If you’ve ever wondered “What is a negative air machine?” or how it differs from positive pressure systems, the answer comes down to controlling airflow. By creating carefully managed pressure environments, these systems either prevent contaminants from escaping or block them from getting in.

We at Air Filters Northwest have witnessed firsthand the importance these systems have taken on—particularly since the COVID-19 pandemic. What was once treated as an added precaution is now an essential measure for keeping high-risk patients safe and health care settings secure.

What do “positive” and “negative” pressure mean?

Imagine a room as a balloon. If the room is just a little bit higher pressure than the hallway, air wants to leave the room — that’s positive pressure. If the room is just a little bit lower pressure than the hallway, air comes into the room — that’s negative pressure.

• Positive pressure rooms push clean, filtered air outward, keeping contaminants out.
• Negative pressure rooms pull air inward, keeping contaminants in so they don’t spread to adjacent spaces.

These pressure relations are designed meticulously — small variations (usually expressed in Pascals or water column inches) suffice to guide airflow in the correct direction. Health guidelines reports provide recommendations for particular pressure differences and ventilation rates based on the room’s function.

What is a negative air machine, and how does it work?

A negative air machine (sometimes called a negative air unit or NAU) is basically a high-capacity fan + filter system that exhausts air out of a room to create a vacuum effect. You seal off the room you wish to isolate, join flexible ducting from the NAU to an outdoor discharge point, and the machine sucks contaminated air out of the room, draws it through filters (typically HEPA), and expels it outside or feeds it through further filtration. The outcome: the room remains under negative pressure, not allowing contaminated air to travel into hallways or other rooms.

Key points about negative air machines:

• They commonly use HEPA or ULPA filtration to remove particles and microbes.
• They’re portable and can be quickly deployed for short-term isolation or construction/renovation.
• When applied in the context of airborne infection isolation, regulation normally suggests attaining 12 air changes per hour (ACH) for new or renovated isolation rooms (6 ACH can be used in older designs). That 12 ACH is a typical planning goal in the event of an outbreak and for AIIRs.

Where you’ll see negative vs positive pressure room setups in healthcare

Negative pressure rooms (also known as Airborne Infection Isolation Rooms — AIIRs) are used if the patient might be releasing airborne infectious particles you don’t want to disseminate. Common examples:

• Patients with active tuberculosis
• Suspected or confirmed airborne viral infections (e.g., some stages of COVID-19 management)
• Rooms used for aerosol-generating procedures

Hospitals construct such rooms for negative pressure and high ACH (typically 12 ACH; see above) and for exhausting air directly outside or through HEPA filtration before reuse.

Positive pressure rooms (sometimes referred to as “protective environments”) are the reverse: employed when the patient needs to be shielded from external contaminants. Examples:

• Bone marrow transplant patients
• Some ICU rooms for immunocompromised people
• Operating rooms and certain labs (to keep sterile air in)

Positive pressure prevents unfiltered hallway air from entering the protected space.

Positive air pressure vs negative: pros, cons, and practical tradeoffs

Both approaches are engineering tools to control risk. Here’s a plain comparison:

Positive pressure (protects the room contents)

• Pros: Keeps outside contaminants away from vulnerable patients and sterile areas.
• Cons: If applied incorrectly, it can force contaminants into surrounding areas if ventilation is not functioning. Needs regular filtration and pressure checks.

Negative pressure (protects the outside from the room)

• Pros: Contain infectious aerosols, protecting staff and other patients. Great for isolation.
• Cons: Needs safe exhaust routes; merely dumping dirty air outside without filtering can produce other problems if not handled properly. Also requires vigilant sealing and monitoring to retain the negative differential.

Healthcare facilities often run both systems concurrently in various areas: ORs and some ICUs use positive pressure, and triage, AIIRs, and some procedure rooms use negative pressure.

When a negative pressure machine is the emergency hero

During public-health surges or building construction, at times, hospitals will repurpose regular rooms as temporary negative-pressure isolation areas through the use of NAUs. The CDC and ASHRAE strategy for “expedient” or short-term isolation includes:

• Achieving at least 12 ACH if possible (that’s the baseline for new AIIR construction).
• Ensuring exhaust is safely routed (or HEPA-filtered) and that pressure differentials are measured and recorded.

Temporary negative pressure rooms are not “set and forget” — they must be continually verified, as minor leaks or system modifications can reverse the pressure relationship and compromise protection.

Respirators and room pressure: how positive and negative pressure relate to PPE

Pressure-controlled rooms and respiratory protection work as layers:

• Negative pressure respirators (like N95s): The wearer inhales, creating negative pressure that pulls air through a filter. They require a good face seal and fit-testing.
• Positive pressure systems (PAPRs – Powered Air-Purifying Respirators): These use a battery-powered blower to pass filtered air into a helmet or hood and create minimal positive pressure within the headgear. PAPRs minimize breathing resistance and usually don’t need a snug face seal, and so are easy to wear for lengthy procedures or individuals with facial hair.

Thus, although room pressure determines who is in the room to be protected, respirators guard those within the room or those entering the room. The combination of a negative-pressure room (to isolate the source) and proper PPE (to guard the caregiver) provides the most protection during high-risk procedures.

Practical tips for facilities managers and clinicians

1. Measure, don’t guess. Use differential pressure monitors and record ACH where possible.
2. Route exhaust safely. Don’t simply exhaust contaminated air into shared spaces; use outdoor discharge or HEPA/ULPA filtration.
3. Plan for anterooms. Anterooms provide a buffer and help keep pressure relationships stable during entry/exit.
4. Train staff. Staff need to recognize pressure failures and know the PPE expectations for each room type.
5. Use NAUs wisely. They’re excellent for temporary isolation and outbreak surge capacity — but treat them as engineered controls requiring verification and oversight.

Making the Right Choice for Your Facility

Deciding between positive and negative pressure systems or whether you need both takes a level of experience that accrues from decades of working in the real world. Each facility presents its own set of challenges: building age, HVAC layout, patient mix, and budget all come into play.

At Air Filters Northwest, our methodology begins with thorough site surveys that assess your unique requirements and challenges. Whether you are retrofitting an existing facility or building new construction, we will collaborate with you to create systems that offer maximum protection within budgetary limits.

Ready to see how positive and negative pressure systems can boost safety and efficiency at your site? Call us at (503) 968-3261 to arrange your all-encompassing site survey.

Common FAQ