Indoor is always higher ppm (how much depends on many parameters) without proper ventilation. „Proper“ should include a „Heat exchanger“ thus you don’t need to reheat fresh air.
Still, it will add some 80ppm over the amount you have today. There's a huge amount of disagreement over how much CO2 is harmful, but it tends to happen over numbers way above 800ppm.
If your room has 2 times the open air concentration, and you are concerned if it's 2.0 times or 2.2 times, you should already be dealing with the problem.
According to https://www.co2meter.com/blogs/news/carbon-dioxide-indoor-le..., at 1000 ppm people start getting drowsy. Let's assume that a decent indoor environment has 300 ppm more CO2 This means that our threshold for when people start getting drowsy even in decent indoor environments is when atmospheric CO2 reaches 700 ppm. For reference, it is currently around 420 ppm, and pre-industrial levels were 280 ppm.
The 300 ppm offset compared to the outside air is naturally just an arbitrary number, everything up to 1000 ppm (meaning everything up to 580 ppm more than atmospheric levels) is considered "acceptable". That means any increase in CO2 concentration will take an indoor environment which used to be considered "acceptable" and make it cross the threshold into "unacceptable". An indoor environment which would've been at 900 ppm around the industrial revolution (280 ppm) would've crossed the threshold when we surpassed 380 ppm (which was in 1965 according to https://www.statista.com/statistics/1091926/atmospheric-conc...).
let's compare the past 20 years. In 2004, the concentration was ~377 ppm. That's 47 ppm lower than what was in 2024. An indoor environment which was "borderline but acceptable" at 955 ppm CO2 in 2004 would've crossed the arbitrary 1000 ppm threshold by now, and therefore would benefit from a CO2 scrubber. The next 20 years will likely have a higher increase than the past 20 years, so there will be a larger range of currently acceptable indoor environments which will cross the 1000 ppm threshold by 2045.
TL;DR: It's complicated, 20 years is arbitrary, but as CO2 concentrations increase, indoor quality gets worse so indoor environments which were already bad will become worse. 45 years is a more realistic estimate for when your typical good indoor environment will become unacceptable, but it's a gradient.
https://gml.noaa.gov/ccgg/trends/
Extending the current exponential for 20 years, we get into the 500ppm region.
I don't think that's enough to need scrubbers.
Indoor is always higher ppm (how much depends on many parameters) without proper ventilation. „Proper“ should include a „Heat exchanger“ thus you don’t need to reheat fresh air.
Still, it will add some 80ppm over the amount you have today. There's a huge amount of disagreement over how much CO2 is harmful, but it tends to happen over numbers way above 800ppm.
If your room has 2 times the open air concentration, and you are concerned if it's 2.0 times or 2.2 times, you should already be dealing with the problem.
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According to https://www.co2meter.com/blogs/news/carbon-dioxide-indoor-le..., at 1000 ppm people start getting drowsy. Let's assume that a decent indoor environment has 300 ppm more CO2 This means that our threshold for when people start getting drowsy even in decent indoor environments is when atmospheric CO2 reaches 700 ppm. For reference, it is currently around 420 ppm, and pre-industrial levels were 280 ppm.
From https://www.climate.gov/news-features/understanding-climate/..., the pessimistic projections suggest that we may reach our 700 ppm threshold by roughly 2070; 45 years from now. (The graphs are hard to read precisely)
The 300 ppm offset compared to the outside air is naturally just an arbitrary number, everything up to 1000 ppm (meaning everything up to 580 ppm more than atmospheric levels) is considered "acceptable". That means any increase in CO2 concentration will take an indoor environment which used to be considered "acceptable" and make it cross the threshold into "unacceptable". An indoor environment which would've been at 900 ppm around the industrial revolution (280 ppm) would've crossed the threshold when we surpassed 380 ppm (which was in 1965 according to https://www.statista.com/statistics/1091926/atmospheric-conc...).
let's compare the past 20 years. In 2004, the concentration was ~377 ppm. That's 47 ppm lower than what was in 2024. An indoor environment which was "borderline but acceptable" at 955 ppm CO2 in 2004 would've crossed the arbitrary 1000 ppm threshold by now, and therefore would benefit from a CO2 scrubber. The next 20 years will likely have a higher increase than the past 20 years, so there will be a larger range of currently acceptable indoor environments which will cross the 1000 ppm threshold by 2045.
TL;DR: It's complicated, 20 years is arbitrary, but as CO2 concentrations increase, indoor quality gets worse so indoor environments which were already bad will become worse. 45 years is a more realistic estimate for when your typical good indoor environment will become unacceptable, but it's a gradient.
https://en.wikipedia.org/wiki/Carbon_dioxide_in_the_atmosphe...
Just extrapolate.
I was also a bit skeptical, but chatgpt gave a pretty good answer I think: https://chatgpt.com/share/69553e26-ea28-8011-bc17-8658fbea4e...
Buildings with higher people/sqft could already take advantage of indoor co2 scrubbers today.