Manufactured homes either have vents above bedroom doors, below them or both. This is to facilitate proper ventilation and airflow between rooms and help HVAC systems function more efficiently. Newer manufactured homes have the vent or “transfer grille” above the door as stick-built homes do. Older models or “mobile homes” may have a larger gap of one to three inches between the bedroom door and floor rather than a louvered vent above.
These overhead vents you find above doors are also known as “transfer grilles.” They are meant to provide an opening from the bedroom to the hallway for your air to come back and out to the air conditioner, handler or furnace, as the conditioner blows air into the space — all happening even as the bedroom door is closed!
Older models, rely on widening that door to floor gap by one to three inch. This slit under your doorway (or simply opening the door regularly) may be the cheapest solution but provides less privacy and renders less effective in the air return. This leads to the room being pressurized and not being as well air conditioned compared to those that have a regular exchange of airflow (1)
Why does a HVAC system need to push air out?
Air blowing in needs to replace the air coming out. Therefore, having a gap under your door at the very least helps that existing, stale air inside to escape the room. This then allows your HVAC system to blow in new, conditioned air into the enclosed room.
Newer homes with a transfer grille above the door facilitate air flow even when your HVAC systems are shut off. This is due to the principle of the “stack effect” wherein naturally, warm air rises and goes up to the louvered vent overhead, while cool air sinks down and can escape to that slot gap beneath your door. (2)
These vents and openings are basically having your air circulate naturally, which then help your HVAC system function properly. In fact, these aren’t limited to manufactured homes. You can find some of these under door gaps and transfer grilles in your stick built home as well (especially those with central air conditioning). (3)
As HVAC systems modernized into more energy efficient models, home construction also evolved to have several “air return registers” scattered across homes both site and factory built.
Having a transfer grille is great in giving natural air circulation even without the help of electrical or mechanical systems.
As you can see from the diagram above, the “stack effect” created by warm air rises, cool air falls, naturally causes the air to move and circulate around the home, across, up and down… without any electricity!
It greatly helps that all openings and joinery are constructed tight and sealed well to prevent any air leaks and maintain high efficiency of natural thermal comfort.
Of course, opening a window and door would be the simplest way to expel that stale air and humidity. However, transfer grilles and slots can provide this air change even with your doors and windows shut, giving you some seclusion.
An exhaust fan in your bathroom or kitchen may also do the trick. Exhausts are absolutely needed for rooms without natural ventilation (or a window). (4)
How many vents should you have in your home?
A good rule of thumb would be having one vent installed every 150 square feet of area or having a minimum of eight vents. (4)
Why is ventilating your living spaces so important?
Stale air can feel uncomfortable but can also be unhealthy as we’ve seen in this recent pandemic. Our air needs to regularly change and circulate, which our HVAC systems and air-conditioners do. However, open windows, vents and transfer grilles naturally “condition” your air without the use of any power and are integral in having a healthier home.
- McGarry, R., & Madsen, G. (2018, July 27). What is the purpose of the vent grille over the bedroom door? Retrieved June 2022, from https://www.howtolookatahouse.com/Blog/Entries/2018/7/what-is-the-purpose-of-the-vent-grille-over-the-bedroom-door.html
- McGarry, R., & Madsen, G. (2018, October 3). Why is there such a big gap under the doors inside a mobile home? Retrieved June 2022, from https://www.howtolookatahouse.com/Blog/Entries/2018/10/why-is-there-such-a-big-gap-under-the-doors-inside-a-mobile-home.html
- O’Dell, C. (2020, February 26). Why is the gap so wide under the doors in my manufactured home? Mobile Home Friend. Retrieved June 2022, from https://mobilehomefriend.com/why-is-the-gap-so-wide-under-the-doors-in-my-manufactured-home/
- Admin. (2019, November 23). Why do mobile homes have vents above the doors? Quick. Retrieved June 2022, from https://quick-advices.com/why-do-mobile-homes-have-vents-above-the-doors/