Thanks, I didn’t know there were different kinds. Did some quick googling and it’s not easy to tell what tech they are. Can you list a couple of examples of ones with acoustic CO2? I tried a veris since you mentioned it and it was Dual beam on-dispersive infrared (NDIR), diffusion sampling.

I would strongly recommend using the acoustic CO2 sensors. A sealed house with natural materials can have low VOC, not feel stale, but still have high CO2. Cheaper CO2 meters will use VOC levels as a proxy for lack of outside air, or use FLIR and are erratic and super sensitive. I was working on CO2 mitigation at work, and had picked up one of those new acoustic chip CO2 meters to meet some stringent certification code, decided to try it out at home and was shocked. Calibrated at work with a known 750 ppm source, was reading 1090 to 1200 in bedrooms. I had taken so much care to seal and insulate, I had robbed myself of any fresh air in the winter. I am installing a standalone ventilator and exhaust, HRU, and a 1.5 KW variable output in-duct heater. I have a veris CO2 in duct meter to go into the exhaust. It’s 0-10 VDC output will turn on a RIB sequencing relay to start fans, heat will control to a base 65F discharge temp if needed after HRU coil. I am using a pair of variable speed AC infinity fans to balance out 80CFM of outside air, 20 CFM per occupant, and will trim it slightly positively pressured to maintain that zero infiltration. The Veris and RIB should keep it +/- 50 on 500PPM. Filters on supply and exhaust to keep the coils clean.

I would love to monitor it when I’m away for 1-2 months, but I still don’t think I’d turn it all the way off.

Another article about BSC-001 summarizes: “6. There’s no provision for ventilation based on sensors of CO2, relative humidity, or any other indoor air components.”

In BSC info sheet 001, I saw: “..Performance Criteria stipulates that the 62.2 ventilation flow rate be delivered at least one-third of the time and that whole-house distribution is required. ”

Are there known arguments AGAINST smart ventilation? Perhaps related to unintended consequences, sensor reliability, or practicalities of getting them implemented correctly?

Allison wrote:
> In smaller houses or apartments with several people, ventilation is more important because there’s less total air in the house and a higher density of pollutants.

Absolutely. And when the time comes to sell my home, I intend to discuss ventilation options with the buyer, and it will be covered in my yet-to-be written House Operation Manual (shouldn’t every house have one?). My point was not that ventilation is never necessary, but simply that I remain in Joe’s camp in terms of degree.

More than that, I agree with Todd’s point… that we need smart ventilation that can react to conditions, e.g., C02 at a minimum. Designing 24/7 ventilation to address the worst possible occupancy or contaminant scenarios works against all the work we’ve done to reduce the energy loads and address HVAC oversizing.

David, yes, COVID-19 is definitely a big part of the reason for my change of position on ventilation rates. But it’s not just that because high-MERV filtration can remove a lot of the virus-laden particles. Since I’ve started watching CO2 rates, I’ve realized how difficult it is to get air changes in a house. Even leaky houses don’t do it well because you’re relying a lot on wind and stack effect.

Yeah, the need for ventilation varies with the situation. Two people in a large house don’t need much, as is the case in your house. But what if you have a dinner party? Or sell the house to a family of 6? In smaller houses or apartments with several people, ventilation is more important because there’s less total air in the house and a higher density of pollutants.

Regarding the accuracy of CO2 monitors, yeah, they’re not laboratory-grade instruments. But it’s easy to check and calibrate them by taking them outdoors. If you leave it outdoors for a while and it’s reading 600 ppm, that’s not good. If it’s close to 400 ppm, it’s OK.