Besides ionizers being a bad idea in general, they certainly wouldn’t help reduce Ryan’s carbon dioxide levels. The only way to do that effectively is by ventilating with outdoor air.

Simon, that is bad advice. Ionizers may create ozone. They create chemically active ions that can produce harmful byproducts. And their effectiveness is not proven. I’ll have an article on this topic next week.

Ryan, have you heard of air ionization? I believe the use of a Global Plasma Solutions (GPS) product may help you on multiple fronts as far as IAQ improvement in your home.

The first thing to understand is that CO2 sensors can be misleading due to a number of factors. The second is that how leaky the home is needs to be measured to understand what is happening. First I would check calibration on the CO2 sensor. What does it read outdoors (away from sunlight)? What does it read when the family is gone from the home for a few hours? It should read around 350-400 outdoors, maybe even a bit lower in rural areas with vegetation. It should drop significantly when out of the house.

2002 is an in-between time for home construction. It could be anywhere from 1980s standard to relatively tight. Windows might not be a good indicator. My recommendation would be to get an energy rater (HERS) to evaluate the tightness and quantify how many ACH happen naturally and how many need to be delivered by the HVAC.

Even in the best ventilated buildings, occupancy can overwhelm ventilation for short periods. Depending on how many people are in the room, even an ERV might be insufficient to keep CO2 low. If the problem is localized, circulating fans (ceiling or portable) will help with mixing and reduce levels.

Hope this helps!

Trying to figure out the best way to increase ventilation: not too worried about covid because we’re staying completely isolated, nobody else is coming in. Opening opposite windows for cross draft does make a dent but isn’t ideal in the middle of winter. The only outdoor air supply in the HVAC is one of those old fresh air dampers into the return plenum with a weighted lever that’s supposed to be automatic but doesn’t work: I have it jammed open since I got the sensor, which helps. Have also turned on “circulate” mode on our fancy thermostat which says it will run the fan at least 1/3 the time, which helps. But, still getting the numbers above (was even worse before!)

Anything we can do besides get an erv or hrv? Not very interested in having service people in our home right now… Fan in the intake duct controlled by furnace fan combined with a servo on the damper? (Yes, I’m one of those electronics diy types, my sensor and dev board it’s connected to are from Adafruit) Fan speed change? (It’s an ECM aka DC brushless motor, two level gas forced air with central ac, 2500sqft) We’ve got a nice aprilaire cleaner in the system that I’ve put the Merv 16 filter in, so our particulates are awesome when not cooking: nearly unmeasurable counts and pm1.0/2.5/10.0 ratings of 0. (Yay more sensors) Glad it’s no worse for allergies sake (if you see no other humans, remaining respiratory trouble is allergies!), but the filter does nothing for co2 naturally…

Are there professionals that could maybe inspect and recommend for stuff like this via video call? I’m in the dangerous position of having enough sensors to know I’ve got a problem, but not enough knowledge to fix it without calling in another human being into my building envelope which is nope.

Thanks for your very informative blog! (Got a low level CO meter because of it, though wimped out and got the approx $70 Forensic Detectors one from Amazon. Sitting at zero, so pretty sure that’s not behind the headaches)

Spend a few minutes reading
Spend a few minutes reading about the effect of high CO2 on sleep and cognitive performance and I suspect most will want better than “the worse you can legally build”. I’d also assure 15 CFM of fresh air/occupant to each closed door room.

Roy, I agree with
Roy, I agree with conservation of mass, but there is a key word we are discussing here: change. Air introduction rate and air exfiltration rate are equal, but neither of them adequately describes change. Change means a qualitative difference- the air entering is different than the air leaving. Imagine entering air has blue smoke and room air has red smoke. What is the rate at which the room air will turn blue? Of course the answer depends on dilution, displacement, and circulation. Adding 100 cfm of blue smoke does not mean 100 cfm of red smoke is leaving (unless you have perfect displacement).

I do agree more with you than Allison on dilution though. Perfect displacement can only happen with perfect introduction- a wall of pin-size nozzles perfectly creating a displacement zone. But we have diffusers- made to mix the air for thermal comfort. Well mixed air will ultimately remove more pollutants, because displacement will be imperfect and leave dead zones that will retain all the red smoke. At least if it is well mixed, I know the rate of decrease and it will decrease evenly everywhere.