Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1227696
60 | March 2020 A CO2 anecdote. We have a client whose teenage son competed nation- ally to solve Rubik's cubes. He started going outside for a few minutes before competing and saw a noticeable drop in his solve times. I thought that was wild. Ideally we want to keep CO2 levels low, a realistic level is in the 600-800 ppm range indoors. How Much Does It Take to Keep CO2 Levels Low? This is geeky, but bear with me a mo- ment. There is an international stan- dard for fresh air in residential homes called ASHRAE 62.2. This standard is partly based on research from a few homes in the 1980s using expensive monitors (one of our clients was part of the study, in fact.) It's also partly based on educated guesses which has led to some vigorous debate. 62.2 works out to 30-100 cubic feet per minute (cfm) for most homes, de- pending on the house size and number of occupants. For reference a standard builder grade bath fan is rated at 50 cfm, although they usually flow less than half that because of poor install practices. The trouble is, getting above 30 cfm pretty much requires a separate piece of HVAC. This can easily add thou- sands to the cost of your HVAC system, and adds another fairly major piece of equipment to maintain, and eventually replace. My friend John Lapotaire, an air quality consultant in Florida, did a small study of 21 Florida homes 7 years old or newer with ERV or HRV fresh air systems (energy recovery ventilators or heat recovery ventilators). 19 of those 21 systems had failed, primarily due to the filters not being changed and the motors burning up. None of those homeowners was aware of the failure. Hearing that, and also armed with 40 $200 indoor air quality monitors, I wanted to see just how much fresh air really was required to keep CO2 lev- ple need to breathe, as do pets and, very importantly, combustion appliances such as furnaces and water heaters that use a fuel, along with gas stoves and gas dryers. I should mention that houses do need to stay dry, which we discussed last time with dehumidification. All sorts of bad things happen when houses get too damp (or dry!) as you saw in the ASHRAE chart above. Making your home tighter increases your ability to control your indoor environ- ment without regard to what is happening outside. As we make houses tighter, in order to get better control over heat, air, and moisture flowing in and out of them to provide better comfort, it's important to bring in some outdoor air so the air inside doesn't get stale or unhealthy. Fresh air is also known as "mechanical ventilation" in the HVAC world. What does stale air look like? One of the common proxies is carbon dioxide. For more about proxies for healthy air see To Catch a Health Thief from the May 2018 edition. Carbon Dioxide Makes You Dumber Lawrence Berkeley National Labs found that even modestly high levels hurt our brain function. Atmospheric levels are about 400-500 parts per million (ppm) of CO2. At 1000 ppm effects were seen, at 2500 ppm cognitive functions fall off a cliff. https://newscenter.lbl.gov/2012/10/17/elevated-indoor-carbon-dioxide- impairs-decision-making-performance/ 2500 ppm might sound high, but if you sleep in a closed door room with your spouse/significant other, you're probably hitting at least 1500, and 2500 is possible. If you have a boiler without forced air, you're almost certainly breaking 1500 ppm at night (those open windows during Spanish Flu times helped with this.) If you have forced air and it runs a lot, those levels are likely lower because they are being mixed throughout the house and evened out. Sadly, most systems are drastically oversized, so it may not run enough to drop those levels. Could your sleep be improved by lowering CO2 levels in your bedroom?