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High levels of carbon dioxide in house

My house has high levels of CO2 / carbon dioxide, every room is between 1100 ppm to 1200 ppm according to an air quality test I had. There are only 2 grown occupants and it's a 1000 sq. ft. brick house. No pets or plants, gas stove / furnace / water heater.

The basement was the only area that had between 900-1,000 ppm of CO2. I've read ASHRAE likes to see under 1000 ppm of CO2. We do have headaches & drowsiness but aren't sure if it's strictly from CO2. For reference, our CO (carbon monoxide) numbers were all under 2 ppm.

According to an energy audit, the house is 0.32 NACH, so I believe that is pretty airtight. There is no mechanical ventilation aside from a bathroom exhaust fan.

I've read that more occupants = more CO2, and poor ventilation can also lead to more CO2 levels (as compared to the outdoors). How would a building pro decide if the levels are high due to low ventilation, or if perhaps there is some source of CO2 within the house aside from the occupants?

I am questioning if it is purely occupancy & low ventilation because rooms that we aren't in as frequently had higher levels of CO2 than our bedroom. Do people commonly monitor CO2 levels within the home?

Asked by Jeff Watson
Posted Sun, 03/09/2014 - 15:21
Edited Mon, 03/10/2014 - 05:04


34 Answers

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Who did the test, and with what?

Answered by David Meiland
Posted Sun, 03/09/2014 - 16:02

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We used to live with very much higher levels of CO2 in submarines, for weeks on end, and came to no harm. I seem to recall that CO2 is harmless at the levels you have measured.

Put a few house plants on your sunny window-sills, and see if that reduces the levels.


Answered by Anthony Ratliffe
Posted Sun, 03/09/2014 - 16:04

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Your air leakage rate of 0.32 (nat) ACH is roughly equivalent to 5.4 ach50. Many homes are tighter.

Nevertheless, your home should have a mechanical ventilation system -- especially because you are concerned about indoor air quality. For more information, see Designing a Good Ventilation System.

ASHRAE sometimes recommends monitoring or measuring indoor CO2 levels, but the reason for the monitoring is not because the CO2 is particularly dangerous; it's because CO2 levels are a useful indicator of whether or not the building has a functioning ventilation system.

Here is information from an ASHRAE technical document: "CO2 at the concentrations commonly found in buildings is not a direct health risk, but CO2 concentrations can be used as an indicator of occupant odors (odorous bioeffluents) and occupant acceptance of these odors."

Here is some information from the Minnesota Department of Health: "Carbon dioxide is not generally found at hazardous levels in indoor environments. The MNDOLI has set workplace safety standards of 10,000 ppm for an 8-hour period and 30,000 ppm for a 15 minute period. This means the average concentration over an 8-hour period should not exceed 10,000 ppm and the average concentration over a 15 minute period should not exceed 30,000 ppm. It is unusual to find such continuously high levels indoors and extremely rare in non-industrial workplaces."

Answered by Martin Holladay, GBA Advisor
Posted Mon, 03/10/2014 - 05:23

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David, Anthony, and Martin - thank you for your advice. Overall, I would just like to say I am not trying to approach this from a health point of view or that I think the levels are approaching hazardous ranges. The 1200ppm readings I've read can cause drowsiness. However, my primary concern is if these CO2 measurements are a direct result of occupancy & low ventilation and how would one be able to verify that. Are there some building science or simple ecological factors going on that may be also contributing to CO2?

David - these measurements were performed by a Professional Engineer (PE) who was using a "GrayWolf Advanced Sense IAQ" device.

Anthony - I understand. I'm not at the point where I believe there is a serious health hazard as I know I am far away from dangerous levels.

Martin - The one thing that I wish I had was a control sample of the CO2 outside of the house. I don't exactly live on a quiet dead-end street. I'm on a 4 lane busy city street. If the area just has more CO2 in the air, and if I were to invest in something like an HRV, wouldn't I potentially be increasing levels of CO2 & other contaminants?

I guess what I am trying to say is I am interested in what is happening within / around the building from a technical perspective, as opposed to the usual health/money-concerned homeowner. If there's a source of CO2 aside from occupancy that can be reduced, I'd just like to find it. I'm just a curious person & like to learn how things work so that I can be able to describe it.

Answered by Jeff Watson
Posted Mon, 03/10/2014 - 08:08

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It would certainly be useful to know the outdoor CO2 level--surprising he didn't check that. Any humidity readings? Knowing indoor RH compared to outside would be another indicator of whether ventilation was the issue, or perhaps something else. Personally I doubt you have an unusual indoor source of CO2. What analysis did your PE offer?

Answered by David Meiland
Posted Mon, 03/10/2014 - 11:51

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David, humidity readings were performed. With an indoor temp of 73-74 degrees Fahrenheit, RH was between 28% and 29%. For reference, outdoor temperature was 20 degrees @ 62% humidity (absolute?) according to Weather Underground historical/hourly data. The only analysis provided was more in the form of "crack a window" vs. identifying the source of CO2. Maybe he didn't want to speculate to protect himself or something.

Answered by Jeff Watson
Posted Mon, 03/10/2014 - 14:19

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Hit up and look into their units. They're not the
cheapest thing to have, but it's a nice bit of reassurance you can
sit on a prominent shelf in your living space and monitor what's
going on.

With the minimum levels set for CFM and time-interval set in my
HRV I'm at maybe 0.1 ACH or less, single occupant, no pets or plants,
I run between 700 - 900 PPM when the house is closed up. But I've
let it run up over 2400 PPM with the ventilation shut down on occasion,
if for nothing else but to see how I could drive it, with no ill
effects. Place smelled a little stuffy, but I probably had similar
conditions for much longer periods before the HVAC retrofit [that's
a guess, as I didn't have the meter back then].

Don't worry about room-to-room. Partial pressure of any gas tends to
disperse fairly evenly until it finds a hard air barrier. It's not
intuitive, but I found that opening windows in seemingly unrelated
areas of the house would start lowering CO2 levels pretty rapidly
where the meter is. I'd consider CO2 levels as a strictly secondary
priority to monitoring interior humidity, which is likely to have
a more profound effect on where you live, but it is nice to be able
to quantify how your own existence is affecting the IAQ.


Answered by Hobbit _
Posted Wed, 03/12/2014 - 00:17

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Thanks _H*. I think I'll invest in a CO2 meter - taking measurements myself to study steady-state as well as cause & effect situations are probably the only thing that will settle my nerves. I'm a numbers nerd so I need to quantify things. There are a couple of areas I was interested in hearing if they would be mentioned in being contributors (e.g., sump pit that serves a basement half-bathroom, high efficiency furnace venting). Guess I'll just have to buy a meter & measure.

Answered by Jeff Watson
Posted Thu, 03/13/2014 - 09:39

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I bought a CO2 meter. Some observations & request for comments:

1) Right before going to sleep it read 1100ppm in our bedroom and when we woke up, it was 1300ppm. This is with no heat running overnight, all windows closed up.

2) With the furnace on, the CO2 levels start to steadily rise. I need to do a test to see if the levels rise with only the air handler on (no gas) to see if this is just diffusion, or if the burning of gas is dumping CO2 back into the equation.

3) The kitchen had the highest levels...about 1200ppm steady-state. Rose to 1900ppm with the oven on & one window open.

4) In my laundry room which has a sink & ejector pit (which serves a basement bathroom), the levels were high as compared to the rest of the basement.

Can I get some ideas as to CO2 contributors? Searching the internet, Google always thinks I meant to say carbon monoxide.

Any comments?

Answered by Jeff Watson
Posted Fri, 03/28/2014 - 09:30

Answered by David Meiland
Posted Fri, 03/28/2014 - 09:55

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I have a CO2 meter in my house.
My experience is that the major CO2 contributors/generators are gas ranges and people. I was surprised to learn how quickly a gas oven will increase indoor CO2 concentrations and how slowly it dissipates. In our house, running the gas oven for an hour, even with the kitchen exhaust fan on, the indoor CO2 would jump from 500 ppm to 2,000 ppm. And it would not get back down below 1,000 until the following afternoon. We moved since then and don't have gas appliances anymore and do have an ERV and now our CO2 usually ranges from 400 ppm to 600 ppm. But the CO2 can still shoot up over 1,000 and even 2,000 ppm if we have a bunch of people in the house and the widows are closed.
I didn’t have the CO2 monitor in the previous house (the one with a gas range) over a Thanksgiving holiday, but since then have wondered whether high CO2 levels from running the gas oven and gas stovetop burners for hours that day with a crowd of people in the house ever contributed to the lethargic after-Thanksgiving-turkey-dinner feeling!

Answered by Nelson Labbe
Posted Fri, 03/28/2014 - 15:02

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Great info, Nelson.

Answered by David Meiland
Posted Sat, 03/29/2014 - 20:40

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Thanks for the links David & thanks for sharing your experiences, Nelson. I can only dream of the day an HRV is within reach in my old house. For now I'll just have to stick with leaving a window open before I leave for work in the morning....that's the only way my CO2 concentration reaches 500ppm. Seeing how high the levels rise when using the oven probably explains why I always feel sleepy when the oven is on, and why 75% of the time, I fall asleep after eating if it's something we cooked at home. Definitely keeping a window open if the stove is ever on.

Ventilation rates seem to only account for people and/or number of bedrooms. I guess the only way to really test if I have contributors aside from people & lack of ventilation is to vacate the house & expect that the CO2 level will eventually reach equilibrium. If my house's ventilation is rated at 0.32 NACH, after 3.125 hours, I should expect equivalent CO2 readings inside & outside the house.

David, your links mentioned CO2 in soil, sewer gas, and decomposition as other sources. I might be going crazy but all of those I wouldn't cross off my list: I have a damp basement, not sure I have a properly vented sewage ejector, and there is a dead tree in my yard. All three of those things could add up & possibly introduce CO2 within the building if it gets in through the concrete foundation.

For example, while sitting here typing this I am the only one home with all windows closed. I had been sitting here for 20 minutes and CO2 was at ~1000ppm. I cut the furnace on and the CO2 is now rising faster. After 10 minutes it's at 1300ppm. If I am the only contributor to CO2 I would have assumed the room I'm in would have the highest level and once the furnace is on, that the level would drop as the air is distributed throughout the house. But it seems like the opposite happens.

Answered by Jeff Watson
Posted Sat, 03/29/2014 - 23:01

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what type and age is your furnace and water heater? Direct or atmospheric vents?

Answered by Bob Irving
Posted Sun, 03/30/2014 - 12:36

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Bob, furnace was installed in October 2013 and is a nat gas 92% model with intake & exhaust pvc pipes. Water heater is the typical 40gal atmospheric vent.

One hypothesis is that once the air handler is on, leaky ductwork pulls in CO2 from the basement and the CO2 concentration equalizes between basement & main floor. To test this, I left all the windows open in my basement yesterday to let it naturally ventilate. When I cut the furnace on after some hours, the CO2 on the main floor did not rise as fast as I had previously observed. So I'm wondering if this is just a simple case of leaky ductwork that pulls in basement air. After all CO2 is denser than O2 so maybe it just pools in the basement.

I've never heard anyone recommend ventilating their basement (let's just assume it's unfinished/unoccupied), but I presume this is only a concern since I don't have balanced ventilation. I guess when people say exhaust-only ventilation doesn't always give you good air is true - I've noticed that running my bathroom fan increases CO2 concentration just like running the air handler does. Eventually I do reach a point where the meter stops rising as fast.

I did perform a separate test where I aired out the house til it was down to 700ppm, closed all the windows, set furnace to OFF, came back 3 hours later and the meter was sitting at 720ppm...negligible. Once we got home is when it started to rise.

So I guess this really is just about ventilation; just that I didn't think about my basement & leaky ductwork & how they might impact ventilation strategies (such as exhaust-only) on the main floor.

In another eye-opening test, I had pretty much all of my windows open, and my meter refused to decline in its reading. I thought the meter was broke, so I then placed it right next to a window to which it started to fall sharply (as expected). Put it back in the middle of the room and it shot right back up to over the 1100ppm reading it had before. Even turned on the bathroom fan & it went nowhere. Not sure how to explain that one.

To really conclude if I have an additional CO2 contributor, I need to air out the basement, close all the windows in the basement, and start the meter; leave and come back after some time to see the rise, fall, or absence of change.

In my case, I guess the only guaranteed way of reducing CO2 in my house is by cracking a couple of windows (on the main floor AND the basement)!

Answered by Jeff Watson
Posted Mon, 03/31/2014 - 09:54

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Jeff... have your tested CO2 and shutting off water heater? Also... somewhere you might have posted but do you have a gas stove/oven and do you have pilot lights anywhere burning?

Answered by aj builder, Upstate NY Zone 6a
Posted Mon, 03/31/2014 - 12:17

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Good point....water heater was not shut off during any of my tests. It does have a pilot so I guess that's one contributor that I didn't think about.

I do have a gas stove but the burners don't have standing pilots; electronic ignition.

Answered by Jeff Watson
Posted Mon, 03/31/2014 - 21:51

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After that last post, I did some closer monitoring in the utility room in the basement and I think I've found possible mold.

My CO2 meter pointed out an area in the utility room right under my bathroom where the tub would be. A couple of the wooden floor joists have some black powdery-looking hairy stuff on them. The main supply & return ducts for my furnace are less than 2 feet away from this area.

So it kind of adds up with what I was experiencing; basement was not necessarily poorly ventilated, I just think I have pollution (if it's mold that gives off CO2). With the (unsealed) ductwork in close proximity, probably explains why I would see a jump in CO2 levels on the main floor which then evened out.

As one of David's links above mentioned decaying vegetation as a source of CO2, wondering if the high CO2 is from the wood rotting, or if mold gives off CO2. I have seen articles that only seem to indicate there's a correlation between CO2 and mold, but not necessarily if mold is the causation of CO2.

For now, I am just going to leave the window to the utility room open if we are home & figure out if I really do have mold. If it's true, that $150 CO2 meter surely served its purpose!

Answered by Jeff Watson
Posted Tue, 04/01/2014 - 08:19

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Your posts raise many questions. I'm not convinced that the CO2 levels you are recording are high enough to be worrisome.

That said, if you are worried about the indoor air quality in your basement utility room, it makes sense to seal your duct seams with mastic.

Answered by Martin Holladay, GBA Advisor
Posted Tue, 04/01/2014 - 08:42

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Just a small update. Went on a 3-day vacation. Left all windows closed. R60 in the attic. Unfortunately I forgot to turn off the 40gal gas water heater.

Is it odd that when I turned my CO2 meter on when returning, that the CO2 levels were higher than 3000ppm (the max my meter can read)? Since the house is not 100% air tight, I would assume that eventually the levels should decrease by natural ventilation. And now that I have R60 in the attic & better attic floor air sealing, I am struggling to keep the levels down by having to run my 80cfm bathroom fan almost non-stop (with a window cracked). Levels don't seem to move at all running the fan with all windows closed.

Answered by Jeff Watson
Posted Sun, 08/24/2014 - 21:09

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Your home sounds like a candidate for sick home syndrome. Before anyone jumps to conclusions, based on your last post you may consider having the exhaust flue(s) and mechanicals examined by a professional. May I also suggest now that you have super insulated your home that you hire a blower door tester to examine your home. The fee is low enough to afford. Many utility companies offer it free or at a discount to their customers.

For the other posters above... Never under estimate the effects on human CO2 exposure. Not all bodies behave the same as others. Here's a guide which you all may find useful;

Answered by Richard Beyer
Posted Mon, 08/25/2014 - 00:31

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I agree sick home, people only exhale small amounts of CO2. Easy to do in tight homes that bring in so many toxins from manufactured products. These reports, people acting like doctors interpreting internet write-ups, do not put your life in their credibility. Through out history they have been proven wrong, I don't even waste my time reading them and spend more time taking the toxins out of my building products myself, especially for tight homes, that only makes common sense. Ventilating outdoor toxins into the home may make it worse. You, we in the USA, design our homes with the wrong materials.

Calcium Oxide or Lime used to bind hempcrete, limecrete, lime wash, lime mortars, natural lime paints, etc.. in many homes in Europe and around the globe are known to be CO2 negative. The slagged lime wants to revert back to limestone (rock) and needs CO2 to do it.

Look at the link below, the "High Calcium Lime" by Greymont when hydrated with water should take down your CO2 levels naturally with no ventilation or moisture control (which the lime does also when combined with a silica(sand, hemp,etc) It be interesting to see how much in a closed room test. You simple get some at a feed and seed or big box store. You do not want to dolomitic with magnesium oxide or "S" mortar mix. 'N' mortar is also high calcium lime if it is available. It is only around $10/50 lb bag. Build a cast out of 2 x 4's of a decent size. Of course if your whole house was constructed of HCL you probably would not be posting your Co2 issue out here, but it would be interesting to see what block size takes down what ppm, test. There are other manufactures of high calcium lime besides Greystone you can easily find locally. Afterwards, lime based washes or paints that are very cheap, or casting a partition wall of limecrete may help reduce your problem, again test a room. If you decide to try this please report back.


The oldest uses off lime exploit its ability to react with carbon dioxide to regenerate calcium carbonate.When lime is mixed with water and sand, the result is mortar, which is used in construction to secure bricks, blocks,and stones together. Mortar is initially a stiff paste that is laid between the bricks. It gradually hardens, cementing the bricks together. At room temperature, the reaction of lime with carbon dioxide is very slow. It is speeded by mixing lime with water. When lime is mixed with water, it forms calcium hydroxide, called slaked lime.

Answered by Terry Lee
Posted Mon, 08/25/2014 - 09:00
Edited Mon, 08/25/2014 - 09:21.

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The next time you hire someone to do a comprehensive cause and corrective analysis of both indoor and out, hire an industrial hygienist not a PE.

Answered by Terry Lee
Posted Mon, 08/25/2014 - 09:29
Edited Mon, 08/25/2014 - 10:09.

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Richard Beyer/Terry Lee - to date, I've had 4 inspections - initial home inspection (visual), energy auditor(measured), environmental engineer(measured), and a subsequent home inspection(visual). The equipment is fine in terms of exhaust. I only started taking note of CO2 after the environmental engineer came out & indicated elevated levels.

Today we left the windows open while we went to work. Levels were at 600ppm upon returning. Closed the windows, cut the A/C on, and we were at 900ppm after half an hour. If I do have a sick home, how do you locate where the CO2 is coming from?

Terry Lee - I'm not too sure what you're saying - are you saying my brick house was possibly built with lime mortar & that can explain why I have a lot of CO2?

Answered by Jeff Watson
Posted Mon, 08/25/2014 - 22:26

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Lime mortars use atmospheric CO2 to cure, but the rate at which it takes it on after the mortar has been curing for even a few months is irrelevant in terms of bringing down your interior CO2 levels.

If you mix up fresh batches of lime mortar in your house and maintain low ventilation rates it'll probably be measurable, which is why he's recommending applying a lime-crete parge or something. Even if that worked in the short term (and I'm not going to waste the time to even estimate it, but would be happy to let Terry Lee show the math) it's a band-aid. Lime mortar eventually cures, and stops taking on more CO2 after many decades, but. most of the up-take occurs in the first few months. It's a logarithmic decay- the fact that it might take 100 years to fully cure is irrelevant, since the majority of the CO2 uptake happens in the first few days/weeks. I'm sure it'll work great for the first week though.

Dealing with the sources are a better approach, but as band aids go it would be better to keep a bunch of house plants, which also take CO2 out of the atmosphere. Unlike lime mortar it will continue to do so for as long as you keep the plants going, and the rate can be adjusted by the amount of live foliage you have.

Answered by Dana Dorsett
Posted Tue, 08/26/2014 - 13:19

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Dana, not at all most of the Lime Association and European reports show that it takes years for lime to fully cure, and as it hydrates it prolongs it again. It is hydraulic in the sense that it is always curing and self-healing hence why it makes such a great mortar, when in the presence of humidity. Sounds good anyway, and so does you theory as usual, but I personally do not buy any of it. I never seen any data anywhere. Just pondering today the whole hempcrete concept and finding a cheaper alternative. It is not the lime that pulls the CO2 out of the atmoshere, it is the calcium oxide that was turned into a hydrate upon heating and hydrating, or slating. Lime can mean alot of things, dolomitic lime has magnesium oxide (MGO) which is more of a cement and calcium oxide. The mineral source, purity from mining and kiln manufacturing has alot to do with it. Add all that to a house and who knows what the outcome. I'm not sure where you are getting your set and cure times, but, I doubt you have tested your times in a lab moreless home, forget math you won't get there with it alone. As I advised, and good advise it is, the best so far with regards to calcium oxide cure time and ability to remove CO2, get a high calcium "N" morar, make some blocks put it in a room and test it over time. If it works add more, test, if work you now know what to do. $10 bag, cheap!

Answered by Terry Lee
Posted Tue, 08/26/2014 - 15:27

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Terry Lee: So, if I'm reading this right you are proposing an untested solution, hoping to get data back from the homeowner with the problem?

I've acknowledged that it takes years (decades) for lime mortar to fully cure, but it's the rate that matters when dealing with an acute CO2 source. (I don't suppose you've measured the actual curing times either, eh?)

It takes a lot of house plants to make an appreciable ding in the concentration levels, but they remove some amount of VOCs too. It's clearly better to figure out the source and deal with it rather than going at it with any band-aid approach.

Of course, taking the adage "The solution to pollution is dilution." to heart, heat recovery ventilation would be pretty reliable solution even if the source is never discovered.

Answered by Dana Dorsett
Posted Tue, 08/26/2014 - 15:52

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Terry Lee - I'm not too sure what you're saying - are you saying my brick house was possibly built with lime mortar & that can explain why I have a lot of CO2?

No, I'm saying run a test with Calcium Oxide also known as "Quicklime" In mortar it comes as a "TYPE N", Agriculture products as "High Calcium Lime"...both with over 86% "calcium oxide" look at the label, you get at Lowes or Home Depot, or a feed and seed. You do not want "Calcium Carbonate" it is not lime. Cast into test blocks shown in my attachment, the two whites ones are lime. Monitor the CO2 PPM levels over time report back. Try a closed room at first. It cost $10 for a 50 lb bag, add a little water but not too much so it dries fast and remains castable...use a 2x2' box made out 2x6's with a plywood or OSB floor. I casted mine vertically in forms, you can do that too. You remove the forms after 1-2 hours or when it gets hard. Plants add oxygen to the air, this will remove CO2. You can do all kinds of things with them to add to the home.

What IAQ meter are you using, where did you get it and what did it cost? Perhaps I'll run the same test.

Ideally, according to many sources had you build your walls and roof like my pics we would not be talking right now. Too late for that, you can try an expensive ventilation system but this is cheaper, and I do not think you will find anyone to guarantee a CO2 drop from it or plants or any so called band-aid, they are band-aids at this point. Rennovations is the word I like to use :)......I'm doing one now testing lime additions so if you want lets compare notes.

Answered by Terry Lee
Posted Tue, 08/26/2014 - 15:57
Edited Tue, 08/26/2014 - 16:05.

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Jeff Watson, When was the last time your meter was calibrated? Did you drop it or place it next to a large source of heat? Did you blow on the receiver? How was it packaged when you received it? The same questions could be asked of the engineer who alerted you to the problem.
I can place a meter in an open room and receive measurements of 550ppm, sit 3 people down and have a conversation for 2 hours and watch the meter spike at 750ppm and higher depending on the ventilation in the room.(aka.. ACH)
Depending on where you live the outdoor CO2 will measure 350ppm to 450ppm. It's when the meter goes past 1000ppm when you need to take action and add more ventilation. A small home will also read higher than a large home. Those are only examples. If you have spray foam insulation this will contribute to elevated CO2. Just my opinion.

Answered by Richard Beyer
Posted Wed, 08/27/2014 - 22:45

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Hi Jeff, stepping back for a moment, I just want to point out that your natural ventilation isn't running all the time, it is temperature and wind dependent. If inside and outside temperatures are equal and the wind isn't blowing, there is basically no air exchange. The blower door test is a simulation of wind driven air leakage and the actual air exchange number derived from it is based upon gas diffusion tests that combine both stack effect and wind over some time period. Thus, presuming that the house exchanges at 0.32 NACH: "If my house's ventilation is rated at 0.32 NACH, after 3.125 hours, I should expect equivalent CO2 readings inside & outside the house." Is not valid. In fact it is between difficult and impossible to know what your air exchange is at any given time.


Answered by Bud Poll
Posted Wed, 08/27/2014 - 23:49

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Thanks for all the answers. I'm learning quite a bit, which is fun & interesting.

[Terry Lee]
Ok, I understand you're giving me a possible solution of removing CO2 from the building. Would this be a permanent solution or something that I'd have to do periodically? Will the building eventually reach a point where I no longer have to create these casts (assuming the building materials are the primary culprits behind my high CO2)? My guess is that I'd have to do this...forever?

The meter I am using: "AutoPilot CO2 Monitor". +/- 5% accurate under 2000ppm, max reading of 3000ppm, 2 minute response time. Cost me around $120. I know it's not one of those fancy expensive meters, but for the purpose I use it for, it does fine.

[Richard Beyer]
I haven't calibrated the above meter since getting it a couple of months ago. I know it's a cheap meter but I don't have any reason to believe it is malfunctioning based on its ability to provide consistent readings. It's not surprising to see the meter sitting at 2000ppm after waking from a lot of sleep & still feeling sleepy. The PE had some super fancy meter that I believe used lasers or something internally to do the readings which were pretty much instantaneous. Keeping levels under 1000ppm is extremely difficult with only 2 people home in the mornings, evenings, and overnight unless we leave all windows open around the clock. Levels don't drop as much overnight even with windows open. This is a small house. Our bedroom is 12'x9', 8' ceilings. 1000sqft total, brick house. Bath is 5'x7', bath fan is 80cfm and vents out the roof.

[Bud Poll]
That makes sense & it's originally what I would have thought (that NACH is just some guesstimate). However, if it's just a guess, it makes me wonder what is the true standard that we can all compare to to assess how air-tight our homes are? I thought NACH was because the blower door just tells leakage with forced pressure, so it's artificial in a sense because you won't find an average home with a fan in the door putting the home under 50 Pascals 24/7. I feel like getting a new blower door test done is what is needed, but at the same time, what is this really telling me aside from the fact that I might have less "air holes"? It doesn't feel like it's telling me how poor my ventilation might be without mechanical means.

However, ventilation is separate from the goal of my thread. My main concern is this: in a 1000sqft brick home with drywall & 2 inhabitants overnight, a couple hours in the morning, and a few hours in the evening, what would be the amount of CO2 released by these inhabitants through respiration if the home was in-fact at a NACH of 0.32 after an hour if the starting volume of CO2 was 1000ppm and there are no gases being produced through the burning of fuel as well as no plants being present in the home with all windows closed?

Answered by Jeff Watson
Posted Sat, 08/30/2014 - 12:54

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1 m^3/h = 0.7063 ft^3/hr

CO2 emission = 0.08 m^3/h = 0.057 ft^3/hr = 3.42 cfm

room = 12 x 9 x 8 ft = 864 ft^3

1000ppm of CO2 in a 864 ft^3 room = 1000ppm/1000000 * 864 ft^3 = 0.864 ft^3 CO2

0.864 ft^3 / 0.057 ft^3/hr = 15 hours


My stab at answering the question of how long does it take for a human to increase the concentration of CO2 by 1000ppm in a 12 x 9 x 8 ft room is 15 hours (assuming current concetration of CO2 is 0 and ventilation rate is 0).

Given that the CO2 emission of a person = 0.08 m^3/h

1 m^3/h = 0.7063 ft^3/hr, so CO2 emission = 0.057 ft^3/hr

If the room is = 12 x 9 x 8 ft = 864 ft^3, and assuming its current CO2 concentration is 0 (highly unlikely), it means that 864 ft^3 room would contain:

1000ppm = 10^-6 * 864 ft^3 = 0.864 ft^3 of CO2 if a CO2 meter read 1000ppm of CO2.

If a person exhausts CO2 at 0.057 ft^3/hr, it would then take:
0.864 ft^3 / 0.057 ft^3/hr = 15 hours

to get the room to 1000ppm of CO2. With two people, 7.5 hours.

However, if the baseline CO2 concentration is the level outside (let's say 400ppm), that means humans would only raise the concentration by 600ppm. So in that 864 ft^3 room at 1000ppm of CO2 (0.864 ft^3), the person only contributed to 60% of that, or 0.518 ft^3 of CO2.

0.518 ft^3 of CO2 / CO2 emission rate of 0.057 ft^3/hr = 9 hours. Two people, 4.5 hours.

So this says CO2 rises from 400ppm to 1000ppm in 4.5 hours without ventilation if two people were present. Now if you bring ventilation into the mix, to get the room back down to 400ppm of CO2, 518 ft^3 of room air would need to be exchanged. An 80cfm bath fan equals 4800 ft^3/hr. If this fan can exhcange 4800 ft^3 in an hour, 518 ft^3 would be exhausted in only 0.108 hours or 6 minutes.

Any of this make sense? Where are my errors because I don't feel that I experience the above rates in actuality.

Answered by Jeff Watson
Posted Sat, 08/30/2014 - 16:48

Helpful? 0

Jeff Jeff Jeff

IMO... you may not have a real problem... have you ever checked CO2 in the last ten places you lived in your whole life? I think you are OK, and your meter is getting you concerned for not.

for fresh air, crack a window, install a Zehndar ERV/HRV or Panasonic HRV... live outside, move into a green house

and put the meter up for sale on Ebay.

Answered by aj builder, Upstate NY Zone 6a
Posted Sat, 08/30/2014 - 20:15

Helpful? 0

I think people take blower door test, ventilation rates, CO2, and miscorrelate them. The subject matter here is chemistry , mixing CO2 gas with air dynamics is not to be taken lightly as simple CFM formulas. Blower door test, NACH, ACH, CFM…..ASHREA 2.2, BCS-1, make no correlation to CO2 found inside the home and outside since that would be very difficult. The chemistry and air dynamics is too complicated to use math alone as Jeff did that is your error, that is why the bathroom fan makes no sense.

At end of a build, or renovating a situation like this where the homeowner is concerned or dd not consider Co2 negative materials, there should be an actual IAQ test and study as part of the decision making process to restore the building to acceptable limits, especially in small air tight construction. Adding recirculating air and expensive HRV-ERVs are not a fix all, as shown in Jeff’s case where it appears circulating outside air is not taking the levels down much chemicallly. One could spend a lot of money in a HRV to get little effect, when exhaust only and NACH is all that is needed. Those limits should be as low as possible, and will vary from person-to-person.

Lime will indefinitely absorb C02 (no maintenance req'd), you can find the test results and data on the National Lime Associations website and publications not out here, or at any of the top USA lime manufactures third party testing on their site(Graystone, Carmeuse, etc), or around the globe like Europe which does not produce as pure of a lime as we do according to the NLA.

What correlation can be made as far as lime quantity to levels absorbed, again complex chemistry and dynamics, who knows. The best effort is stop wasting time with math and as I said, run some test. Cast a simple block note the drops, the time it took or less to crunch the numbers that make no sense as I also said you did it be done. If it works, and there is massive amounts of empirical testing to say it does, there all kinds of ways to cast-sculpt-paint lime into a home, search the internet, it depends on what ways you can find in your situation. Lime is a great product we lost sight of long ago, has a history that dates back BC.

I need to do some research on meters before I buy, I want an industrial one not agriculture. If you do the test please report the results. You can also get some large abs pipe cut the sidewall length wise, hose clamp it, pour the lime, remove the clamps and release a cylinder casting for test. Might be easier than using wood formwork.

Casted hemp with lime walls and roofs, limecrete, lime paints, etc sure is looking more and more appealing, especially in tight construction.

Answered by Terry Lee
Posted Sun, 08/31/2014 - 07:36
Edited Sun, 08/31/2014 - 08:18.

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