Most literature on HVAC systems call on homeowners to seal every hole and crack in the house to prevent air leakage, as this would compromise energy efficiency. Naturally, doors would be closed as well, as they could let a great deal of air escape.
While this advice is based on solid principles, there are other factors at work that should be considered when it comes to heating and cooling, with air pressure being a primary concern.
The Pressure To Stay Cool
With everything sealed up, the pressure inside a room will slowly escalate. This is the natural consequence of continuously pumping a massive volume of air from the outside into a finite space. This can be relieved by opening the door from time to time while the occupant is awake. However, the door would presumably stay closed during bedtime. The pressure may eventually reach the point where additional input from the AC forces air to escape through whatever small openings it can find. Conversely, the rest of the house will experience a negative pressure that would suck in air from the surroundings. Outside air is likely to come from passageways like a furnace flue or a chimney.
This outside air carries with it pollutants that have not been filtered out. In fact, the number of contaminants is likely to be higher because of the way in which they got inside. The humidity and carbon monoxide levels will also spike, possibly causing alarms to set off. The health risks involved have to be taken seriously. Try to feel for incoming drafts near the areas mentioned to see if your house is experiencing this problem. Open the bedroom doors to see it anything changes. The reduced air pressure should stop the house from drawing air through these undesirable pathways.
So how does the issue get resolved? Opening the doors would be a good start, but leaving them this way throughout the night may not be feasible to most people. The key thing to remember is that we simply need to increase airflow by a small amount to prevent pressure buildup. Transfer grilles are good candidates for a remedy. They do not compromise privacy and are fairly easy to install.
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