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Recently, I've been measuring the CO₂ concentration during multiple nights and the levels in the bedroom where I sleep are very high and unhealthy (over 1600 ppm).

CO₂ levels during a couple of days, peaking over 1600 ppm
I use an AirVisual monitor, which is high precision and catches the trends. I opened the window last night, and that's why the CO₂ is lower. But on all the other days, it's over 1400-1600 ppm.

I get a high concentration only when I'm sleeping, so I assume that the CO₂ comes from me. Since the windows are shut and the door closed, the CO₂ gets trapped.

The problem is that during the summer, the temperatures outdoor are over 95 F (35 C) with high humidity, and I have the airconditioning running inside. If I open the window, the heat comes in very fast and then the AC has to do extra work, which means waste of money and resources. And it's the same situation during the night.

How do I get rid of CO₂ inside the house without opening the windows when the weather is hot?

EDIT: After reading all the great suggestions, I have tried a new measurement with the device far away from my bed, so it will not be affected by my breath. I also checked for timers and couldn't find any. Last night I closed the window and the door at around 11 PM and the concentration started to slowly increase. During the night, the CO2 levels increased significantly (see graph below). In the morning, I opened the window and it slowly started decreasing. I have no doubt that there is a lot of CO2 in the room. So my question stands. How to get rid of CO2 or any other gases/vapors for that matter, in a hot, humid climate. Is HRV the only solution?

enter image description here

Physther
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    What kind of device are you using to determine the carbon dioxide (CO2) concentration of 1600 ppm? Are you sure this is accurate? Does the measured level change with time of day? – Jim Stewart Aug 20 '18 at 20:33
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    Measure the CO2 outside the bedroom. If much lower, use a fan to cycle the bedroom air. If similar levels of CO2, then you might have a leaky appliance. Until you figure this out, open a window on both sides of your home. Your health is more important than air conditioning. – John Hanley Aug 21 '18 at 12:32
  • A CO2 peak at 5 AM? Do you have any appliances on a timer doing something around that time? – Mast Aug 21 '18 at 13:23
  • What is your sleep schedule? Graph suggests that you go to bed at 20 and wake up at 4. Or maybe the clock is slightly offset or in wrong timezone? – Agent_L Aug 21 '18 at 14:22
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    @JohnHanley, that's a good idea to measure it outside. Will do that for testing, but I can already guess that it is lower outside because when I open the window, the concentration of CO2 decreases considerably. The Fick's laws are also on my side. I also have a fan running, so it forces the CO2 to go out. – Physther Aug 21 '18 at 14:43
  • @Mast, I'm not aware of any appliance on timer, but will certainly check it today. What appliance that could generate CO do you have in mind? The oven/stove is electric. – Physther Aug 21 '18 at 14:43
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    @Agent_L, at 20 ( 8PM) I enter the room to watch something before sleeping. Waking up at 7 and opening the door. – Physther Aug 21 '18 at 14:44
  • @Physther So the reason of raise is explained, but the drop two hours before you wake up is quite puzzling. – Agent_L Aug 21 '18 at 14:50
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    Where is this sensor physically located relative to you while you're sleeping? If it's on a table next to the bed and you're facing it, you might be skewing the numbers by breathing directly onto it. The drop-off before you wake up could then be explained by you rolling over and facing away from the sensor. Move the sensor around the room and see if the numbers change. – bta Aug 21 '18 at 21:56
  • @bta, that's a very good point and I don't know why I didn't think of it before. It is placed actually next to my bed, close to my head. Will move it away to see there will be a difference. Thanks – Physther Aug 21 '18 at 22:22
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    The first step should be to validate that the readings you're seeing are accurate. Have you had the meter calibrated? What made you think to test the levels? Where is the meter located (i.e., if it is right in front of your face, the levels will be artificially high). If the levels are actually that high, you should have symptoms, like drowsiness and rapid breathing. If this is while you're asleep, drowsiness is kind of covered, but do you ever wake up and notice that you're breathing much faster than you normally do? If you aren't experiencing any symptoms, question the readings. – fixer1234 Aug 21 '18 at 22:39
  • Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/82044/discussion-on-question-by-physther-how-to-get-rid-of-co-in-a-house-with-a-c-in). – BMitch Aug 22 '18 at 00:19
  • Lithium hydroxide canisters, like the space station: https://www.sae.org/publications/technical-papers/content/2008-01-1969/ – Wayfaring Stranger Aug 22 '18 at 03:03
  • Can you provide a source on CO2 concentration and health concerns? –  Aug 22 '18 at 08:04
  • Folks, please refrain from posting answers in the comments. –  Aug 22 '18 at 08:04
  • Challenge to the risks of the "high CO2 ppm" This says that 10,000ppm is safe for an 8 hour period, but it does state that ideally the ppm is below 1000. https://www.health.state.mn.us/communities/environment/air/toxins/co2.html#:~:text=This%20could%20occur%20when%20exposed,dangerous%20to%20life%20and%20health. – UnhandledExcepSean Oct 12 '22 at 03:22

6 Answers6

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You want an high-efficiency heat exchanger.

https://en.wikipedia.org/wiki/Heat_recovery_ventilation

Basically, you pipe in fresh air, but have it cooled before, while you heat out the air that is going out. It's typically installed on central hvac systems.

It needs maintenance to be efficient and it is quite often overlooked by contractors as it's hard to notice when it's not working.

Jeffrey
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That's a really high CO₂ level. You need to figure out what is causing it and fix that, it's not normal.

Gas fired appliances with leaky vents are the most likely suspects — hot water heater, dryer? (Probably not your furnace, since its summer!)

In the meantime I would seriously open some windows and suck it up, that's dangerously high if accurate.

SQB
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jkf
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    This answer is especially correct if you consider the new graph: unless the OP goes to bed at 8PM and gets up at 5AM, a faulty gas cooker seems more likely. – Sanchises Aug 21 '18 at 12:29
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    It is high, indeed. No gas-fired appliances. Electric water heater + dryer , but I use the dryer twice a week and the electric water heater should not produce any CO2 since it's electric (or should it?). I am pretty sure now that I am the source since during the day, when the room is not occupied, the CO2 level is low. Like you suggested, I have decided to keep the window open, even if the AC will work extra. – Physther Aug 21 '18 at 14:50
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    According to this, even the unoccupied level is high: https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms. It's hard to understand why you have such a high unoccupied level. What other source of CO2 could there be? – JimmyJames Aug 21 '18 at 16:51
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    I vote for a highly inaccurate CO2 meter. Get that verified first – Carl Witthoft Aug 21 '18 at 17:25
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    @CarlWitthoft, I don't think the calibration is a problem. I'm pretty sure the values are in that range. The device can also measure PM2.5, which I checked on an air purifier. It shows very good values. I know there are two different sensors but I trust it's a good instrument and it's new (close to calibration time). Besides, I feel very tired at night and I wake up with headaches when the window is closed. With open window, I feel fresh. Either way, the question is how to get rid of CO2 with or without this device. – Physther Aug 21 '18 at 19:35
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    @jkf, 1600 ppm is "you want to fix it"-high, but it's not dangerous: you could probably go your whole life breathing that with nothing worse than the occasional headache. As a point of comparison, OSHA and NIOSH state that long-term exposure should be kept below 10,000 ppm, while ACGIA recommends keeping exposure below 5000 ppm. The "immediately dangerous" exposure level is somewhere around 30,000-40,000 ppm. – Mark Aug 21 '18 at 23:35
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    "That's a really high CO₂ level." [citation needed] – Mazura Aug 22 '18 at 00:06
  • I have a bedroom CO2 meter and I get very similar numbers as the OP. Last night, it peaked at 1500 ppm, daytime levels of ~500 ppm. I don't think there's a measurement issue. And yes, running forced air ventilation (natural duct leakage), bathroom fans, or sleeping with the door open make a major difference. – user71659 Aug 22 '18 at 05:38
  • @Physther (and user71659) are you living in super-insulated buildings? 99.99% of all structures in the USA are not superinsulated, so there's a full air exchange right thru exterior walls , ceilings, etc. something like every 30 minutes. That's why I'm skeptical that just closing window & door will lead to spikes in CO2 levels. – Carl Witthoft Aug 22 '18 at 12:27
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What type of air condition are you using? Some only cool the air inside, while others use fresh air from outside. In a cafe or club there are norms about how much fresh air the air condition must put inside during a given period of time.

I would suggest the following:

  1. measure the CO₂ concentration outside to compare it with your inside CO₂ concentrations.
  2. Measure CO₂ concentration on a Sunday while you stay at home. Does it increase the same amount?
  3. Try to calculate how much O₂ you turn to CO₂ while you sleep and make an estimate of how large the CO₂ concentration should be after one night. If it is much higher than it could be just by your breathing, search for other things that may increase CO₂ in your room.
SQB
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user90188
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    The 3rd point makes a lot of sense and will surely support the idea of me being the source. Will make the calculations soon. Thank you for the suggestion! – Physther Aug 21 '18 at 15:12
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Plants respire throughout the day, producing both O² and CO². They produce much more oxygen than CO² though. It is a good idea to have plants to help with air, but they don't produce enough to make a huge difference. People intake approximately 750L of oxygen per day. We exhale approximately 0.02 cubic meters of CO² per hour. A plant, on average, produces approximately 22L of oxygen per day. It would take a lot of plants to change your room's exchange. That doesn't mean it is a bad idea though. Everything helps. Specific plants exchange better than others, and some help to remove harmful pollutants from the air. Do not fall victim to the myth that plants exchange CO² only at night and that they come even close to an even exchange. They exchange far more oxygen and do help.

Cameron
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I have asthma and an 80% collapsed windpipe. With CO2 levels even within a good range (less than 600 ppm) I become short of breath. I had an erv system(energy recovery ventilation)system installed. Can’t use that during fire season! It hasn’t helped at all and the installers haven’t been helpful in figuring out why an open window does a better job. When I use it Particulate matter increases and opening windows does a better job of lowering CO2. The best idea I’ve found is to reverse a powerful fan out of the window to pull CO2 from the room. In minutes I can reduce the level but I can only rely on this method in the spring and fall unfortunately.

Bev
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  • Just a hint from my chemistry days: CO2 is heavier than oxygen and will settle towards the floor so exhaust low. Google says: "If left undisturbed, CO2 does sink lower to the ground than oxygen, although they both form separate exponential profiles (it's not like the bottom half of a volume is 100% CO2 while the top half is 100% oxygen - they both have distributions that tail off exponentially with height - it's just that the CO2 /oxygen ." I hope that helps. – Gil Jul 28 '21 at 00:30
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You can also try this: Get some plants in places where there's high co2 concentration. If there's no sun, then use plants which are good in that situation.

joga
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    This is terrible advice. Plants do *not* absorb CO2 during the night (they actually add to the problem). Without light there is no way they could do photosynthesis, but being living organisms they need energy to survive. This energy can only come from oxygen in that case. – Damon Aug 21 '18 at 13:09
  • @Damon good point -- plants breathe at night emitting CO2, i.e. they "burn" carbon they have collected from the CO2 when there was light. The net balance for a growing plant is still that it absorbs CO2, but it does that during the day. I once wrote an [answer](https://biology.stackexchange.com/a/53391/6139) about that on SE biology ... – Peter - Reinstate Monica Aug 21 '18 at 16:27
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    You could make a grow-room in a closet so the plants are on cycle where they get lamp light at night and they are in the dark during the day. – Arluin Aug 21 '18 at 18:17
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    @Arluin if USA-based, that's a recipe for a visit from the DEA. – GalacticCowboy Aug 21 '18 at 19:16
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    @GalacticCowboy: Good. They need a talking-to. – Joshua Aug 21 '18 at 19:28
  • @PeterA.Schneider What if one used a succulent, which uses CAM. They breathe at night in order to minimize water loss, so it appears they consume CO2 during the night. – Cort Ammon Aug 21 '18 at 23:48
  • @GalacticCowboy - True. I'm concerned that growing enough plants to manage the CO2 level might look like a commercial growing operation. – Arluin Aug 22 '18 at 17:42