How have you been sleeping? It could be connected to the amount of fresh air in your bedroom!

It turns out that “ventilation” (introducing fresh air into a room) is very important to getting good quality sleep!  As we shared in this article, the amount of carbon dioxide (CO2) in the room is tied to ventilation.  More ventilation = less CO2.  Humans occupying a closed room without introducing fresh air will decrease oxygen and increase carbon dioxide just by breathing.  It’s very rare for rooms and homes to be sealed so tightly that carbon dioxide buildup would cause death, but many studies have shown that increases in CO2 cause cognitive decline during waking hours, and now, disturbed sleep at night.

A new overview and analysis of 17 recently published studies shows that in most of the studies, when the level of CO2 generated by sleeping subjects increased, indicating a reduced ventilation rate, sleep quality was disturbed.  Sleep quality was measured by the percentage of deep sleep, sleep efficiency, and sleep onset latency.  The researchers assumed that if one parameter defining sleep quality was affected significantly, then sleep was disturbed and sleep quality reduced.  

The lowest absolute concentration of CO2 at which a negative effect on sleep quality was observed was 1,000 ppm.  This threshold is actually held by many scientists as the “upper limit” of acceptable air quality during waking hours, so it makes sense that our bodies don’t cope well with higher CO2 at night, either.  (For example, in a 2012 study, 22 student volunteers engaged in a game-like simulation, working at desks in a chamber sealed tightly with a door like that on a refrigerator. Over three short trials, they breathed air containing 600, 1,000 and 2,500 ppm of carbon dioxide. The results were astounding. There were “moderate” declines in decision making performance at 1,000 ppm compared to 600 ppm. At 2,500 ppm, the drop in mental capacity was “astonishingly large.”) (Indoor CO2: Dumb and dumber?)

Back to the sleep study: not all of the studies which showed disturbed sleep quality showed negatively on subjectively assessed sleep quality and on next-day performance.  It may simply be that dreams and memories affect the subjective perception of sleep quality more than they affect objective measures.  

So, we definitely need to put “bedroom ventilation” on priority for getting a good night's rest.  Specifically, making sure that “the outdoor air supply rate to bedrooms succeeds in keeping the CO2 emitted by the sleeping occupants at an absolute concentration below 1,000 ppm.”   Like many other HVAC calculations, this can quickly become complex; in order to calculate ventilation by ASHRAE standards, you need the type of room, number of people in the space, the square footage of the area, and the zone air distribution effectiveness (Ez).  Then, to apply a certain ventilation rate in CFM (cubic feet per minute), you’ll need to know how to measure this, coming through a dedicated fresh-air supply, or through your open window.  This is mind-bending for most people, so we suggest something easier: make a change and measure it!

Since you’re going to be asleep while all this measuring is going on, we suggest a CO2 monitor that tracks the levels wirelessly.  This device allows you to view CO2 levels the next morning with an app.   If they seem to be spiking above 1000 ppm, then increased ventilation is needed.  

How can we decrease CO2?  It’s by dilution (adding fresh air so the percentage, or ppm, CO2 decreases). 

• If you’re blessed to have a window in your bedroom and good quality air outside, it can be as easy as cracking open that window to let the fresh air in.  You’ll want to make sure that it’s safe to do so if you’re living on a ground floor or with young children, by securing the window so it can’t be opened to let anyone in or out.  For this reason we really like Vornado’s selection of window fans–they are slim, weather-resistant and good-looking!

• Did you know that many window AC units are fitted with a “fresh air ventilation” louver?  Here’s a snapshot of where it is usually located.  Note that this only allows outside air in, but doesn’t filter it directly.

• Add fresh air to your home’s HVAC system and let it distribute some to your bedroom.  We have an article to give you an idea of options, but if you are interested in something simple, you can look into these products:

  • AC Infinity inline MERV 13 filter, $126: this product requires an inline fan to help draw in air and push it through the filter.

  • reFresh Outside Air Kit w/ Envirosense Controller & 6 inch Motorized Damper, $194, has the ability to allow intermittent opening when the temperature is inside of your set temperature and humidity parameters, to prevent hot, humid, or freezing air from flooding your house.  

  • The Honeywell Home Fresh Air Ventilation System, $250, with TrueZONE Damper is another programmable damper option that works with your central AC blower to pull fresh air in.  Note that it doesn’t have a filter, so that it will ideally be installed with an inline filter or routed to the return filter. 

  • The 8145 Fresh Air Ventilator w/ Powered Damper & Filter by AprilAire, $319, is a great all-in-one option.  The only drawback is the filter is only MERV 6, which with poor air quality outdoors, does not provide much protection.

Photo by Christopher Jolly on Unsplash