What is Positive and Negative Air Pressure?

If you have an air pressure imbalance in your warehouse, office, restaurant, or other space, you may notice:

• Unusually hot or cold rooms
• Doors open and close when nobody is touching them
• Whistling noises
• Drafts of air

The two types of imbalances are — you guessed it — positive and negative.

To understand this better, think of it like a water bottle. There’s only so much water that can fit in that bottle, just like there are only so many cubic feet of air that can fit in a room.

What is Positive Pressure?

Air is very quantifiable. It’s quantified by cubic feet. There are only so many cubic feet of air that can fit inside a room. When we exceed that number we experience positive pressure. The air has nowhere to go so it finds imperfections, like cracks under the door or windows, to escape.

If you place a spot cooler outside of a room you want to cool and duct in the cold air, you’ll be putting that room at positive pressure. Think back to the water analogy: you’re filling up the “bottle” with cold air. Only so much air can actually fit in the room, so eventually, it will fill with cold air, making it much more comfortable.

What is Negative Pressure?

Conversely, when you pull cubic feet of air out of a room, you experience negative pressure.

Now, let’s say you put that same spot cooler in the room and then duct it out: you’re pushing air out of the room. When the air pressure inside the room is lower than outside the room, you create negative pressure. That air then needs to be replaced from somewhere, and that is usually from outside hot air. The result? A hotter room.

When this happens, your heater or AC has to work harder to counteract the outside hot air being drawn into the space. Ultimately this uses more energy.

Some environments, like hospitals, actually need negative pressure. They maintain rooms where the pressure inside the room is lower than outside the room. If a door is opened, contaminated air from inside the room will not flow into other areas.

Why is it a Problem to Have Positive or Negative Pressure?

Both positive and negative pressure could result in more expensive energy bills for you. Another bad result for businesses is that it can make it harder (or too easy) to open and close doors, which could be an inconvenience or a danger to employees and customers.

A dangerous scenario sometimes happens in restaurant kitchens, where negative pressure can cause backdrafting of appliances, which could lead to a buildup of dangerous fumes like carbon monoxide.

What Causes an Air Pressure Imbalance?

A lot of people think an AC unit or heater can be plugged in and act as a “magic box” that will heat or cool their space with no issues. The truth is, you need to do some of the work to determine the best placement and type of unit for your space.

The most common pressure problems are caused by:

1. Poor Placement: Most commonly, especially with temporary AC and heating units, the problem relates to the placement of the unit. You need to have the right unit for your space and perfectly place it to achieve optimal results.
2. Leaky Air Ducts: Poorly designed or damaged ducts are a common culprit for forcing air somewhere it shouldn’t be.
3. Exhaust Fans: Sometimes a fan will move too much air in one direction. When that air is not redirected it can result in an imbalance.
4. Motor Set Too High: If your AC’s motor is set too high it could be forcing too much air into a room, causing positive pressure.
5. Rising Hot Air: In bigger buildings, hot air often rises to the upper levels, which leaves the lower levels with negative air pressure. If you have combustion appliances, like a furnace, they can also draw hot air up and out of the building through vents, which is another cause of negative pressure.

Get to the Root of a Pressure Problem

With a little searching, you may be able to figure out what the issue is that is causing the pressure imbalance. Adjusting fan motors and repairing ducts are two of the easier issues to correct. In some cases, you just may not have proper ventilation in place or your AC system may not be a good fit for your space. When it comes to fixing the problem, it’s all about correcting the flow of air.

If you are having a negative or positive pressure problem with a Priority Rental portable AC unit or portable heater, we can help! When customers call us with an issue, we always troubleshoot to make sure the unit has proper power, fuel, etc. If the unit is working properly, then the issue is normally that it’s not being used the best way for the space. We help educate our customers on how negative and positive pressure may impact the effectiveness of a unit, which helps them find the best placement for their unit.

Have a question about heating or cooling your business? Contact Priority Rental today!