Air pressure inside the building can be either positive or negative. The air pressure inside the house depends on different factors such as exhaust loads, wind, and air leakages inside the house.
A negative air pressure means that the pressure of air inside is less than the pressure outside, which causes the air to infiltrate the building.
In contrast, positive air pressure builds when the inside pressure is greater than the outside pressure. The positive air pressure pushes air outside the home.
So, which is better: negative air pressure or positive air pressure? What causes changes in air pressure?
What are the steps to create the right air pressure inside the house? You will know the answer in this article.
Positive or Negative Air Pressure: Which is Better?
A house should aim for positive air pressure as it helps improve the indoor air quality. Positive air pressure forces contaminants inside the rooms outside.
In the case of negative air pressure, contaminants such as smoke and other particulates will build-up, which will degrade the air quality inside the house. The building will draw in cold air from the outside through openings and cracks.
The amount of air that is exhausted should slightly exceed the amount of air supplied through breathing or the air conditioner or heating devices.
In other words, the difference between the air exhausted and supplied inside the house should be enough to maintain positive air pressure.
But the positive pressure differential should not be large. This is important; otherwise, it can damage the structure of the house.
Signs of a Negative Air Pressure
- Exterior doors take force to open and close
- Cold drafts inside the house
- Odors linger inside the room
- Visible soot rolls out at the bottom of the gas furnace
- The water heater takes time to warm the water
- Pilot flame does not remain lit
- A musty, stagnant smell
- Exhaust fans are not effective
The results of negative pressure inside the house include health issues, high energy costs, and uncomfortable conditions at the workplace.
What Causes Positive & Negative Air Pressure?
Positive or negative air pressure occurs due to the imbalance between the air entering the room, and the air that is exhausted.
Positive air pressure forces air out of the building through cracks in the windows and doors. It also results in the air escaping outside when someone opens the doors.
The opposite happens in the case of negative air pressure. Air is forced inside due to negative air pressure.
Outside air comes inside the house when someone opens the doors. The air also comes inside the house through the cracks around the windows and doors.
Negative air pressure forces pollutants such as car exhaust, herbicide, pesticide, pollen, and odors inside the building.
Here are some of the factors that result in positive or negative air pressures.
Some of the factors can be controlled while others are due to natural forces such as high wind pressure.
1. Wind Pressure
Wind pressure can facilitate either positive or negative air pressure on one side of the house. It will force air to enter from one side and exit from another.
You cannot control the wind pressure, but you can block it, such as by planting trees or creating a wall.
Sealing the house can also reduce air pressure. You can use a leak detector to find out and plug the seals.
2. Chimney Effect
Air pressure can also be due to a chimney or stack effect. The rise of warm air results in increased pressures on the upper parts of the house.
Due to the laws of physics, the air will be drawn in on the lower portions of the house.
You cannot do anything about the chimney effect. But understanding the effect is important so you know how to create a positive air effect by focusing on other factors.
3. Fireplaces and Stoves
Any appliances that use gas, such as stoves and fireplaces, drive out air outside the house.
Unless they are vented from the outside, gas appliances will force inside air outside the house.
Negative air pressure will cause flue gasses to backdraft inside the houses. This is a serious concern that can have a negative impact on health.
4. Duct Leakage
A leakage in the intake ducts of the ventilator creates negative air pressure. On the other hand, a leak in the exhaust air duct can result in positive air pressure.
Ducts should be well sealed.
You need to get them tested at least once a year. A professional technician will use pressure tests to identify the leaks.
5. Oven Hoods
Oven hoods can also create negative or positive air pressure. You need to run them at a low speed where they can remove the smoke.
A high rate can increase the pressure differential resulting in high positive air pressure.
Also, it is advisable that you put lids on pots. The water will emit less smoke and boil faster. As a result, you won’t have to run the hood at a high speed.
6. Bathroom Exhaust Fans
Some people connect the exhaust fan to a light switch, which can be ineffective.
It’s better to run the fans through a timer or a humidistat that activates based on the humidity level inside.
It will ensure that the fans are not running unnecessarily, which can result in excessive positive air pressure.
7. Central Vacuums
Centralized vacuums with HEPA filters are convenient as they don’t eject airborne particles. However, they also create depressurization, which disturbs the air pressure inside the house.
Using a traditional vacuum is recommended to avoid an imbalance in the air pressure. Most modern vacuum cleaners come with high-quality filters.
It is better to buy a traditional vacuum cleaner than a centralized cleaner.
Just make sure that the MERV (Maximum Energy Efficiency Reporting Volume) rating is above 13 so that it properly cleans the room.
Also read: What Time is Okay to Vacuum in an Apartment?
8. Air Vents
Air vents in most homes take out the air from inside the house without bringing the air back in. Exhaust vents take out the air from the rooms.
Traditional air vents don’t bring back the air inside the house.
The front door inside a house does not open as often as the front door of a store. So, the above are the most common sources of air getting inside and outside the house.
Negative air pressure will result when the sources of air getting inside are more than the sources of air getting outside.
This results in the outside air getting pulled inside from the attic, crawlspace, and cracks around the doors, windows, and electrical outlets.
It brings outside humidity, heat, and pollutants inside the house. The result is reduced indoor air quality.
Moreover, it makes it harder for the heating and cooling system to maintain the desired room temperature.
How to Create a Positive Air Pressure?
The best solution to create a positive air pressure is to use an energy recovery ventilator (ERV) or the heat recovery ventilator (HRV).
Heat Recovery Ventilator (HRV)
HRVs have two ventilation ducts with a heat exchanger at the center. The ducts run between each other and pass between the house interior and exterior.
One duct carries cool fresh air inside the room, while the other carries the stale air outside.
The heat exchanger placed in the middle of the ducts allows the outgoing air to pass the most heat to the incoming air without actually mixing the airstreams.
There is generally a fan or a blower on each side of the duct that accelerates the process of exchange of inside and outside air.
Energy Recovery Ventilator (ERV)
ERV is the alternative to an HRV that works in a slightly different manner to maintain proper air pressure inside the house.
The device transfers the moisture from the outgoing air to the incoming air that helps maintain the humidity levels inside the house.
ERV device is recommended if you live in a hot and humid climate. The device will maintain the proper humidity levels and reduce the load on the air conditioner.
In contrast, HRV is better if you live in a cold and less humid climate.
Using HRVs and ERVs will help keep the room well ventilated. Installing the device may involve a lot of costs.
But the investment is worth it as it will result in a healthy environment inside the house.
Final Remarks about Positive Air Pressure in an Apartment
Maintaining positive air pressure can improve the quality of air inside the house.
It will also result in energy savings as the HVAC device will work efficiently in keeping the rooms at a comfortable temperature.
Keeping positive air pressure is not that challenging as it may seem.
The tips mentioned in this blog post will ensure that the air pressure inside the house is slightly positive resulting in greatly improved indoor air quality.
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