4 ms·

Most residential implementations don't pull in fresh air.

by jms703 4y ago

leipert 4y ago
But in a larger apartment or house it could mean that if you occupy one room, like the bedroom, you get air with less CO2 from other rooms. If you have no ventilation on and no airflow, it must be worse.
jchw 4y ago
Doesn't seem to matter: running just the fans alone is enough to lower CO2 readings in my house. I suspect the main reason is just diffusion of concentrations of CO2.
- dathinab 4y ago
  potentially, the air volume of a room hugely affects how often you have to air the room (but can also making the airing take longer depending on window size, arrangement, wind, etc.) one of the reasons some people swear on living in houses build around 1900 where I live, the larger ceiling height adds air volume (there are other reasons like large windows, wooden floors, etc.).
  - panarky 4y ago
    >> That isn't going to do a thing about CO2 Seems like we're forgetting that the objective is not to reduce CO2, it's to reduce the pathogens in the air. Since it's difficult to measure pathogens directly, we use CO2 concentrations as a proxy, since high CO2 means poor ventilation which means potentially high pathogens.
- rektide 4y ago
  It does matter for sure. At least in a modern/energy-efficient "tight" (as in, airtight) build. You can be right that turning on circulation makes the number go down. But that doesnt matter. Over time the concentration can go up and up and up, even with h"v"ac running. Few residential HVAC systems actually ventilate. The focus on energy-efficiency has been a bit blind to the need to get rid of od co2 & take in oxygen. You can get fancy energy-recovery ventilation (ERV) devices that actually do air-exchange with thermal coupling, to cool or heat the incoming air. But this sort of system is alas exceptionally rare.
  - pgporada 4y ago
    I installed a broan nutone ERV this past summer and it's made a tremendous difference with the CO2 levels in my house. We retrofit spray foamed the house (don't, dumb idea, definitely not the attic if you're reading this) and CO2 would build up in the nursery over night well past 1400ppm according to an AirThings Wave+. Now at night it averages like 800ppm in there. With an ERV, the best thing that I found to do is wire it to my furnace such that when the furnace kicks on, it will trigger the ERV to start. Otherwise you'll get furnace blower cycles separate from ERV cycles and it won't be as effective.
    - ericd 4y ago
      Seconding the large impact of an ERV, the air inside feels much fresher when it's on vs when it's unplugged. I've taken to just running the HVAC fan at all times, regardless of whether heating/cooling is happening. This tends to even out the temperature throughout the house, as well as CO2 concentration, it keeps the air filtering through the HVAC HEPA filter, and the ERV can run continuously, so rooms rarely get above 600 ppm CO2. Unsure about the energy use impact, but the air quality difference is palpable.
    - Danieru 4y ago
      > We retrofit spray foamed the house (don't, dumb idea, definitely not the attic if you're reading this) Can you elaborate? We are considering moving into an older house and renovating. Adding insulation being part of the idea. Our current home has full foam insulation with erv so I am curious what difference you experienced.
      - porker 4y ago
        There's two issues with spray foam insulation: First the off-gassing. It emits a lot of harmful compounds as it cures and I understand the emissions to go on for a long time. So if you mind about air quality it wouldn't be my choice. Second is the potential for damp to build up in the building fabric. The foam is airtight so make sure the ventilation is right on both sides of it. A bonus third is the pain of removing it when you need to do building repairs. With board or batts you can lift them out; with spray foam you have to cut then scrape off.
- EricE 4y ago
  If your co2 is lowering its far more likely you have really leaky ductwork.
simondotau 4y ago
Which is, by the way, insane. Aside from freshness reasons, I live in a mild climate and it's not an infrequent occurrence for outside air to be closer to my target temperature than inside air.

Most residential implementations don't pull in fresh air.

by jms703 4y ago

Most residential implementations don't pull in fresh air.

But in a larger apartment or house it could mean that if you occupy one room, like the bedroom, you get air with less CO2 from other rooms. If you have no ventilation on and no airflow, it must be worse.

jchw 4y ago

Doesn't seem to matter: running just the fans alone is enough to lower CO2 readings in my house. I suspect the main reason is just diffusion of concentrations of CO2.

dathinab 4y ago
potentially, the air volume of a room hugely affects how often you have to air the room (but can also making the airing take longer depending on window size, arrangement, wind, etc.) one of the reasons some people swear on living in houses build around 1900 where I live, the larger ceiling height adds air volume (there are other reasons like large windows, wooden floors, etc.).
- panarky 4y ago
  >> That isn't going to do a thing about CO2 Seems like we're forgetting that the objective is not to reduce CO2, it's to reduce the pathogens in the air. Since it's difficult to measure pathogens directly, we use CO2 concentrations as a proxy, since high CO2 means poor ventilation which means potentially high pathogens.
rektide 4y ago
It does matter for sure. At least in a modern/energy-efficient "tight" (as in, airtight) build. You can be right that turning on circulation makes the number go down. But that doesnt matter. Over time the concentration can go up and up and up, even with h"v"ac running. Few residential HVAC systems actually ventilate. The focus on energy-efficiency has been a bit blind to the need to get rid of od co2 & take in oxygen. You can get fancy energy-recovery ventilation (ERV) devices that actually do air-exchange with thermal coupling, to cool or heat the incoming air. But this sort of system is alas exceptionally rare.
- pgporada 4y ago
  I installed a broan nutone ERV this past summer and it's made a tremendous difference with the CO2 levels in my house. We retrofit spray foamed the house (don't, dumb idea, definitely not the attic if you're reading this) and CO2 would build up in the nursery over night well past 1400ppm according to an AirThings Wave+. Now at night it averages like 800ppm in there. With an ERV, the best thing that I found to do is wire it to my furnace such that when the furnace kicks on, it will trigger the ERV to start. Otherwise you'll get furnace blower cycles separate from ERV cycles and it won't be as effective.
  - ericd 4y ago
    Seconding the large impact of an ERV, the air inside feels much fresher when it's on vs when it's unplugged. I've taken to just running the HVAC fan at all times, regardless of whether heating/cooling is happening. This tends to even out the temperature throughout the house, as well as CO2 concentration, it keeps the air filtering through the HVAC HEPA filter, and the ERV can run continuously, so rooms rarely get above 600 ppm CO2. Unsure about the energy use impact, but the air quality difference is palpable.
  - Danieru 4y ago
    > We retrofit spray foamed the house (don't, dumb idea, definitely not the attic if you're reading this) Can you elaborate? We are considering moving into an older house and renovating. Adding insulation being part of the idea. Our current home has full foam insulation with erv so I am curious what difference you experienced.
    - porker 4y ago
      There's two issues with spray foam insulation: First the off-gassing. It emits a lot of harmful compounds as it cures and I understand the emissions to go on for a long time. So if you mind about air quality it wouldn't be my choice. Second is the potential for damp to build up in the building fabric. The foam is airtight so make sure the ventilation is right on both sides of it. A bonus third is the pain of removing it when you need to do building repairs. With board or batts you can lift them out; with spray foam you have to cut then scrape off.
EricE 4y ago
If your co2 is lowering its far more likely you have really leaky ductwork.

simondotau 4y ago

Which is, by the way, insane. Aside from freshness reasons, I live in a mild climate and it's not an infrequent occurrence for outside air to be closer to my target temperature than inside air.