What Is Negative Pressure And How To Fix It In My AC?

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When you think of the air inside and outside your home, you likely do not consider if there is any pressure difference. While the temperature outside might feel hotter or have a difference in humidity, typically the air pressure will be the same. If, however, you have negative pressure inside your home you will see several differences and potential issues with your AC. Most of the time you can troubleshoot the issue on your own. If you cannot, it is important to give your local HVAC service provider a call.

Air pressure is what causes your ears to pop on an airplane or on a fast-moving elevator. Typically, you do not feel a difference in air pressure when you open your front door to go outside. However, there are times where your HVAC system can cause a difference in air pressure. It results in both positive and negative pressure.

If you have ever had someone claim that they have a ghost in their house because doors randomly open or strange noises happen, it’s almost always due to air pressure. But how do you know when you have a change of pressure within your home? There are easy-to-identify signs – each of which indicates that you likely have negative air pressure inside the house.

Negative air pressure often is just an inconvenience or annoyance. It causes doors to swing open suddenly or it may make opening doors difficult at times (until the air pressure evens out). However, there are other times where the negative air pressure is a much more serious problem, which requires you to address the issue right away. Therefore, it is important to identify the problem at times like this, figure out what is causing it and then go about having it corrected as quickly as possible.

Defining Negative Pressure

negative pressure where the air pressure within your home is lower than what is found on the outside

Both positive and negative air pressure can develop inside your home’s HVAC system. If the air pressure is too high, the increased pressure can force doors to swing open, which becomes a safety hazard.

However, in the event of negative air pressure, it means the air pressure within your home is lower than what is found on the outside. This results in air being pulled into the house to make up for this low air pressure (in a way it creates a minor vacuum). When you have negative air pressure doors that open inward will swing open. It may even become difficult to open the door.

Now, just because you have negative air pressure inside the house does not mean the fault lies within the HVAC system. Often, this is due to other physical aspects of the building itself. However, the negative pressure does directly impact how the HVAC functions, which is why it is important to look into the problem and determine what is causing the issue to have it properly fixed.

Causes of Negative Pressure

negative pressure where the air pressure within your home is lower than what is found on the outside

There are several potential causes behind why you have negative air pressure. First, if you live in an apartment or condo, it is possible you are experiencing this shift in air pressure because of warm air rising within your building.

If your home uses an old furnace or fireplace, both devices pull in hot air through the vents. If the pressure becomes too much, it will generate negative air pressure inside the house.

Apart from using furnaces or fireplaces, an exhaust fan may pull too much air out, resulting in the negative air pressure. This is usually not an issue unless you run a large exhaust fan in your kitchen. The problem with this is it can become dangerous around open flames. So if you are experiencing this negative pressure inside the kitchen, it is crucial that you look into getting the issue fixed immediately. Otherwise, the shift in air pressure may lead to gas explosions around the stove top (particularly if you have a gas or propane stove, not electric).

If the ducts and ventilation system around the house leak, the HVAC configuration may pull in unwanted air into the vents. This may cause the creation of negative air pressure. Combine more than one of these issues together and it may lead to a substantial air pressure problem.

If you have a negative air pressure problem, it puts additional strain on the entire HVAC system of your house. This means that both your furnace and AC work extra hard to heat and cool your home to a desired temperature. The additional strain on your HVAC system reduces the life of all appliances involved. It also increases energy consumption which, in turn, will cause you to pay substantially more on your monthly utility bills. By correcting the negative air pressure problem, you will improve energy efficiency and save money on your monthly finances.


How To Fix The Problem

Most times, the negative pressure inside your home can be corrected. However, if you live in a condo, apartment or any other high-rise building, there is a chance that you cannot do much about it. The change in air pressure comes from the rising warm air. So, unless the property owner installs new insulation throughout (especially between floors), the problem will remain. In most other cases though, you can correct negative air pressure inside your home.

First, you need to have your ventilation system inspected. Cracks within the vents pull in air, potentially leading to this problem. Some cracks you will identify on your own. However, it is often best to bring in an HVAC contractor and have them inspect the entire system. This way, they can not only identify and correct the cracks in the vents, but they can find other potential issues with your HVAC system.

There are times the fan motor speed within the AC is set too high. This forces the maximum amount of cold air into the room, which might be too much for the space. This can occur if you have a larger window unit that is too large for the space. When the fan is turned all the way up, it will cause negative pressure. In these instances you need to reduce the fan motor speed. This may be all you need to do to correct the negative pressure problem.

If the problem is with the exhaust fan inside the kitchen, it is crucial for you to bring in a professional and have it corrected. This is no longer just an air pressure issue but a safety concern. As the shift in air pressure may cause a shift in how carbon monoxide moves, not to mention creating backdrafts while cooking on open flames – all of which can lead to more serious problems. So, if you notice any kind of pressure problems inside the kitchen you need to stop cooking inside the kitchen and contact a service provider right away.

The same is true if there is air pressure problems around your furnace. While your furnace is closed off, the flame should not be exposed. If any kind of leakage occurs around the furnace, it increases the chance of an explosion and the creation of a backdraft. A backdraft during a fire is one of the most dangerous conditions a firefighter will face. This is because gas in the air will surge and push flames quickly through an opening.

When you bring in a professional to service your HVAC system, the contractor will have tools on hand designed to help them pinpoint the exact cause of the negative air pressure problem. If the issue is with the HVAC equipment itself, the technician will identify the issue and go about correcting it. If, however, the air pressure issue is with something else in the house, they may not directly identify it. In the instance where the cause of the negative air pressure is not the HVAC system, it is more than likely caused by the rising of air inside the house. To see if there is a way to correct these problems, you will need to bring in a home contractor.


Negative air pressure inside your home is often an inconvenience and mild annoyance that can get worse if not corrected. It forces doors to swing open involuntarily and may make certain doors difficult to open at times. However, if you are experiencing negative air pressure inside the house, it is important for you to do what you can and correct the problem as soon as possible. This may be as easy as turning down the fan inside a window AC unit or fixing leaks within your vents. Doing both of these things will also simultaneously reduce energy consumption and save you money on your monthly utility bills. In the most extreme situations, negative air pressure becomes dangerous and can put everyone inside the house at risk. Should you run into a negative air pressure problem, it is imperative that you call a professional to find out the cause and correct it right away. If they cannot fix the problem, they will more than likely refer you to the right person for the job.

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