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Commercial Air Conditioning, Commercial HVAC

HVAC Troubleshooting: Negative & Positive Air Pressure Symptoms

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Last Updated on February 26, 2018


negative air pressure

Negative air pressure and positive air pressure can cause all kinds of strange, unexplained symptoms in your store, restaurant, or office, like these:

  • Doors opening magically all by themselves
  • Doors suddenly slamming shut when no one is nearby
  • Doors that are not heavy but you need to be the incredible hulk to open them
  • Whistling and odd noises
  • Random drafts of air
  • Unusually hot or cold rooms

If you’ve been wondering if a poltergeist has invaded your business, relax. There’s no need to call in the ghostbusters; the problem is just your HVAC system. At the root of these unsettling issues is an air pressure imbalance, which can be caused by a faulty or inefficient HVAC system.

In this article, we’ll explore negative air pressure and positive air pressure symptoms, their causes, and how your HVAC company can help.

Unbalanced HVAC pressure causes scary (and expensive) problems.

When your heating, cooling, and ventilation (HVAC) system is poorly designed for the space or just not working properly, you can end up with positive air pressure or negative air pressure.

What is positive air pressure?

If you have an HVAC positive pressure problem, the air pressure inside your space is too high, and air is being forced out. This pressure can cause doors opening outward to fly open by themselves, potentially harming people. It also makes inward-swinging doors require super-human strength to open (and may keep customers out). What’s the link between negative pressure & HVAC? Equipment  problems can lead to positive air pressure. Also your expensive, cooled air is being wasted as it escapes through every tiny opening.

What is negative air pressure?

When you have HVAC negative pressure problems, the air pressure inside your space is lower than outside. The pressure difference causes air from outside the space to be sucked in. In this case, you’ll have inward-opening doors flying open without warning, or people may feel trapped in your establishment because they can’t push the door to get out.

What’s the link between negative pressure & HVAC?Both your air conditioner and your furnace have to work harder to counteract the outside air being drawn into the space because of negative air pressure, using more energy in the process.

Both of these situations can be dangerous to your employees and patrons, and also result in steeper energy bills for you.

Learn more: 10 Ways to Tweak Your HVAC System and Save On Energy Bills

How exactly does air pressure get out of balance?

1. Hot air rising.

Warm air in your building rises to the upper floors, and can result in negative air pressure in the lower areas. Also, combustion appliances like furnaces and large fireplaces draw hot air up and out of the building through vents, causing negative air pressure if they expel too much air out.

2. Exhaust fans.

Like combustion appliances, exhaust fans can remove too much air and cause negative air pressure. This can be dangerous, especially in a restaurant kitchen. Negative pressure can cause backdrafting of cooking appliances, woodburning stoves, and fireplaces, leading to a buildup of deadly fumes including carbon monoxide.

Learn more:
HVAC Safety Tips: Don’t Let Carbon Monoxide Sneak Up On You
What You Don’t Know Can Hurt You: How to Keep Your HVAC System Contaminant Free

3. Leaky ducts.

When your ductwork is poorly designed or has holes and leaks, your air distribution is compromised and can lead to all sorts of air pressure problems. For example, air supplied into enclosed areas of the building (like supply rooms) that have no returns can cause positive pressure in the enclosed space and negative pressure in other areas of the building. Holes in supply or return air ducts cause air to move in the direction of least resistance, causing the air balance issues that you may have mistaken for a banshee. Also remember that holes in ductwork cause a loss of heated and cooled air and higher energy bills.

4. Fan motor speed.

The problem may be as simple as an air conditioner motor that’s set too high. If a blower motor is maxed out and forcing too much air into a room, the result can be positive air pressure and those slamming doors.

Who are you going to call?

Fixing air pressure problems requires some detective work, but can often be accomplished by simple measures like repairing ducts or adjusting fan motors. Sometimes additional ventilation is needed, or your air conditioning unit may not be adequate for your space. It’s all about correcting and controlling the flow of air, something your qualified HVAC company is well-equipped to handle.

Isn’t it time you banished that spook in your store or devil in your dining room that’s annoying your customers and driving up your energy bills?

To learn more about how HVAC issues may be costing your business, grab a copy of our guide to Calculating the Hidden Costs of Poor HVAC Maintenance. It’s got surprising information about the cost of discomfort and its impact on your bottom line.

Get the guide to understanding your HVAC System's hidden costs.