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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

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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
    Commented Aug 20, 2018 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
    Commented Aug 21, 2018 at 12:32
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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
    Commented Aug 21, 2018 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
    Commented Aug 21, 2018 at 14:44
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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
    Commented Aug 21, 2018 at 21:56

9 Answers 9

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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.

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    It would also be useful to transfer the humidity from the incoming air to the outgoing air; can that be done as well?
    – Daniel Griscom
    Commented Aug 20, 2018 at 19:31
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    @DanielGriscom there are variants which do, yes.
    – Harper - Reinstate Monica
    Commented Aug 20, 2018 at 20:02
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    Having a small make up air source can really make the air in your home better +
    – Ed Beal
    Commented Aug 20, 2018 at 20:35
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    Everyone always ignores the V. With today's hermetically sealed houses, you need a fresh air intake even if you don't get an HRV.
    – Mazura
    Commented Aug 21, 2018 at 0:30
  • @DanielGriscom Rotary recuperators reclaim both heat and humidity. Also called "thermal wheel".
    – Agent_L
    Commented Aug 21, 2018 at 14:25
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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.

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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
    Commented Aug 21, 2018 at 12:29
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    I vote for a highly inaccurate CO2 meter. Get that verified first
    – Carl Witthoft
    Commented Aug 21, 2018 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
    Commented Aug 21, 2018 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
    Commented Aug 21, 2018 at 23:35
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    "That's a really high CO₂ level." [citation needed]
    – Mazura
    Commented Aug 22, 2018 at 0:06
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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.
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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
    Commented Aug 21, 2018 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.

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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.

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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
    Commented Jul 28, 2021 at 0:30
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Snake plants might help - they intake Carbon Dioxide during the night and need very little light and water. Read the below research papers:

https://www.ias.ac.in/article/fulltext/sadh/048/0049

https://ntrs.nasa.gov/api/citations/19930073077/downloads/19930073077.pdf

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  • I don't believe that 1) Two plants would have that much effect. And 2) that they actually absorb more CO2 at night than they produce.
    – Rohit Gupta
    Commented Sep 17, 2023 at 13:50
  • Read the research papers.
    – amsquareb
    Commented Sep 22, 2023 at 20:49
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Yeah. CO2 is nuts. I just bought a Carbon Hepa Air Purifier and the minute I turn it off triple fan, the highest setting; an Air Monitor alarm goes off in the bedroom, even though I'm not in there. Basically; the smaller the apartment, the harder you work/breathe/have big lungs and the better sealed it is; the worse it ramps. Well; placed in the centre of the apartment, in the middle of the floor on full 24/7 (it only uses 25 Watts or so); the alarm is off and it's down to about 450ppm. Gonna stick it on a RCD 'cos it's working fairly hard (for when I go out). All's I did was turn it down to No. 2 fan when I went out and I came back to alarms screaming. So; I've solved the problem. I've got more energy, feel more positive and my memory is coming back that I didn't even know I'd lost? I feel a bit trippy and spaced-out but I'm sure I'll get used to it. I wouldn't want to clean too far below 400 because we are designed to absorb/dissolve a certain amount of CO2. I'm not planning on "doing a Michael Jackson" with his pure Oxygen sleep chamber anytime soon. God knows what damage years of sleeping in excessive CO2 has done to me poor, wee brain; but I believe it's healing GREAT! Think CO2 makes us irritable, even spiteful? Damn strangest thing it resolving. The last week has been like watching a movie of irritability passing from me that doesn't amount to anything at all. I wasn't irritable before but it is defo. perfecting my nerves. Hope this helps.

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  • Air purifiers of whatever kind DON'T reduce C02 in the air. C02, Nitrogen molecules and Oxygen molecules are all too small for an air filter.
    – Miguel Lomelí
    Commented Dec 10 at 7:13
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Contrary to popular belief, I think there is too much hysteria over CO2 levels. In some countries, people sleep with bedsheets and duvets over their heads. I can assure you that they do not die, do not go mad and their brain does not suffer.

Sure there is a limit where CO2 is dangerous, but I do no think that level is as low as prescribed by the UN.

Having said that, I have a Mitsubishi HRV system called Lossnay. It feeds my 3 heat pump systems with air. This is because I have a almost sealed house to improve heating efficiency.

I would suggest that you look for something similar.

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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.

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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
    Commented Aug 21, 2018 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 about that on SE biology ...
    – Peter - Reinstate Monica
    Commented Aug 21, 2018 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
    Commented Aug 21, 2018 at 18:17
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    @Arluin if USA-based, that's a recipe for a visit from the DEA.
    – GalacticCowboy
    Commented Aug 21, 2018 at 19:16
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    @GalacticCowboy: Good. They need a talking-to.
    – Joshua
    Commented Aug 21, 2018 at 19:28

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