Monitoring CO2 levels in your home

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Old 04-25-13, 09:50 AM
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Monitoring CO2 levels in your home

There seems to be growing concern that high CO2 levels in your home can be a bad thing.

I recently had the two HVAC units in my home replaced, and as a minor addition, I had the AC people add in an outside air intake to both units. Each goes through an electronic damper, and then feeds into the air intake for each unit. Presently I can open or close the damper with my HAI.

The plan was, since it is often cool here at night, but warm during the day, to suck in this free cooling at night and save some AC costs. For example, last night it got down to 60, but it is supposed to be 90 today. The house never dropped below 77 on the side where I don't have the AC on overnight. If I could drop that 77 to say 70, that would be a big help.

So anyway, I just bought a Honeywell CO2 monitor that will also potentially turn on the ventilation if CO2 levels get too high. It has a relay that can close when CO2 needs to be lowered.

Depending what you read, they say indoor CO2 should be lower than 600 to 800 PPM. Today mine is reading 585 with just me home. I put it outside and read about 440, but I only got it yesterday, so need more research.

As it turns out, the fresh air vents are good, but now I think I need to add an in-line fan in each vent. Presently I need to run my HVAC fan to suck in outside air, but this can be costly, since most of the air it is sucking is not from outside but rather just from the return vents in my house. The in-line fans should work better and be cheaper to run.

So does anyone else monitor their CO2 levels?
 
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Old 04-25-13, 10:19 AM
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I do not. Can be a concern but I figure the doors and windows are opened enough on my house for it to not be an issue.

What's a CO2 monitor cost?
 
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Old 04-25-13, 10:25 AM
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We have a gas furnace & stove and have CO monitors but nothing for CO2.

What are you doing in your home that has you concerned about CO2? Are you fermenting 1'000 bbl of something in your house?
 
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Old 04-25-13, 10:40 AM
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So here is a bit more background so some of this makes a bit more sense. What started this is we had a full utility energy audit before we installed the new HVAC units. That said we were in good shape with insilation, but also that our house was much too "sealed," in fact we have half the air infiltration that was considered normal.

This was always confusing to me because they tell you to seal your windows and door gaskets, but I guess they are now sealed too good. You can't win. Am I supposed to remove my door seals? Crazy?

As a side note, also, my wife is very sensitive to bad air due to some respiratory problems and always has been, and second, although this is rare in AZ, I had my home checked for radon a few years ago, and it was mildly high. I had a vent installed that sucks air out from the crawlspace. Levels now are half what they were. So the tight house was something I though could be addressed with the new HVAC systems I was installing.

When I was pricing HVAC units and talking to installers, I mentioned this finding of the home being sealed too much. None of the four AC companies really knew much about that, but two said they could install an air exchanger for about an extra $3500. I researched it, and found out that most people that have these hate them because they waste lots of energy, and I wasn't sure if there was any way for me to automate the air exchanger, so for the time being, I stuck with the simple damper and air inlet. Initially, saving energy was a bigger goal then ventilation.

I should also say my wife is a teacher with 30 kids and she tends to have many more repository problems at school. Do you ever think the school tested for CO2 or Radon?

The monitor was $250 in eBay. It has a relay that clicks on at 800, 1000 or 1200 PPM of CO2.

Opening windows is an option, but in AZ, I can only do that for a few months a year. Also, the wife has many allergies so easier said then done.

Also, please don't think that high CO2 levels or high radon levels are trivial. Lung cancer deaths in non-smokers is the 6th leading cause of death. And you may want to Google "high CO2 levels." There is much we don't really understand yet.
 
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Old 04-25-13, 10:44 AM
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I don't see CO2 causing respiratory problems, that's not what it does. I would think there's something else (probably particulate in nature) at the school which is causing the problems.

Do you know whether the CO2 levels in your house changed after the radon system was installed? The idea behind them is to create a low pressure zone under your slab which causes air to move from your home downward, which should cause your tight home to 'pull' more air in from the outside.
 
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Old 04-25-13, 10:48 AM
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First, it's easy to confuse carbon dioxide, CO[SUB]2[/SUB], with carbon monoxide, CO.
Carbon monoxide is a product of combustion, among other things, and is extremely toxic.
CO[SUB]2 [/SUB]is basically a harmless gas.

I think you're using CO[SUB]2 [/SUB]instead of CO.
 
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Old 04-25-13, 11:05 AM
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Were not talking about Carbon Monoxide here, its CO2 that people exhale. I'm not sure I would call it a "harmless gas." Maybe you'd like to go in a sealed box with just CO2 and we'll see how long you live?

I am not claiming that CO2 causes respiratory problems, and I don't think there is enough research out there on that. High levels DO cause other problems. Just Google "high CO2 levels" for some recent studies. Also the State of Minnesota must have felt its a big enough problem because air exchangers are now REQUIRED for all new construction. Also most commercial buildings DO have some type of air exchangers, and many believe even these requirements are not enough.

I do not know if the CO2 levels changed when we installed the Radon system. I only received the CO2 monitor yesterday. I DO have a SafetySiren ProSeries radon monitor (great device, by the way) and my radon levels are half what they were. I probably averaged a 5 before, now maybe 2. The legal level before taking action is a 4. Certainly not terribly high, but a bit over the limit.

The radon system sucks air under the crawl space out and vents it outside. I don't think that would change my CO2 levels, but having radon is another reason to want to ventilate with fresh air.
 
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Old 04-25-13, 11:20 AM
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I should also add, you can talk about the level of CO2 in your blood, the level of CO2 in your house, and the level of CO2 outside due to global warming. I am referring to CO2 levels in your house, but note that outside levels are also rising due to global warming. Millions of years ago they thought a normal outside level was 300, today its about 400. My sensor outside reads about 440 PPM. that is a baseline.

Inside CO2 is caused by breathing and a sealed house. Just Google "Sick building syndrome" if you need some info in this area. A "good" indoor level is considered below 600 or 800.
 
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Old 04-25-13, 11:40 AM
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What you mention about sick building syndrom and the requirement for air exchangers is related to things other than CO2 such as offgassing of contents, carbon monoxide, mold & mildew. The CO2 levels in buildings are checked as an indication of air exchange for removal of other compounds not so much the CO2.

Anything in high enough concentration can be hazardous. Oxygen & nitrogen are hazardous or toxic in some circumstances and concentrations. So suppose if you are going to fear CO2 you should also be concerned about other gasses in the atmosphere.
 
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Old 04-25-13, 12:11 PM
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You are absolutely correct. CO2 is really just a proxy for much of the other bad things lurking in your air. I think it was the removal of body odor that initially started people thinking they needed to ventilate. In my home, keeping the radon down is important.

Here is a good link for the effects of just the CO2:
Carbon Dioxide Comfort Levels
 
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Old 04-25-13, 05:14 PM
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Instead of the dampers you need an ERV or HRV system to exchange the air with outdoor but to keep the energy (heat & humidity) in your home.
 
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Old 04-26-13, 12:01 AM
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I did consider an air-to-air heat exchanger, and looked at the pros and cons. A con is the price certainly, and they use a fair bit of power. I had four contractors give me bids for a new HVAC system and none of these contractors recommended one of these. One of them claimed that people disliked them because they wasted power. (Their words, not mine.)

In the end I decided to go with an straight air intake, a damper and a fan. (Actually I have two because i have two HVAC units.) For me this is a better solution because I can run them at night and bring cool air in my house and save energy, instead of just costing more energy.

For example, today, it was 86 out so definitely AC season, but it got down to 60 overnight, and without AC my house got down to a low of only 76. So there is some free AC out there I could take advantage of. I realize this won't work year-round (average low in July and August is 83) but if I have to pull in some 83 degree air, and hour or two, that is still cheaper than an air exchanger.

I should add, a Phoenix attic can get to 150 in the summer. Even if I insulate this air exchanger, I have trouble believing it will be able to to efficiently drop incoming air to 80 degrees, no matter how efficient they say they are.
 
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Old 04-26-13, 06:48 AM
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ASHRAE recommends under 1000PPM. I test for this ever time we do air testing just to have a baseline. even at 1500 I don't get worried as long as it is short term.

We test for co2 because its an easy to measure substance that lets us no that there could be other pollutants at elevated levels.

trying to keep your home under 800 ppm is crazy.
 
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Old 04-26-13, 07:30 AM
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Hi anog, sounds like you are having fun:0. But getting involved in these issues is good as most people never give it a thought. I kept notes while reading up to here and have 14 questions, but will focus on the start.

You say you had a utility energy audit. Not always, but all too often those are not the best, so did they give you any numbers, like CFM50, ACH50, ACHn, so we can judge how tight your home really is. Unless your home was built to extreme measures to specifically make it tight, it is doubtful it is. The normal threshold (old) is 1 complete change of air every 3 hours. Give me the total volume of your home, with and without the basement. That with the CFM50 number and I can tell you where you stand.

Also, what combustion appliances to you use, like a gas furnace, gas water heater, other?

Bud
 
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Old 04-26-13, 09:59 AM
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Honestly I wasn't thrilled with the home audit. It was one of the utility sponsored ones, and they were recommended by the HVAC company I eventually picked. They gave me some numbers but failed to explain what most indicate. Overall I would say a waste of money, even if the utility paid for most of it.

Anyway,
Recommended Infiltration CFM50 Flow is 5322
Whole House CFM50 Flow, @ 50Pa, is 2160
Duct Leakage, @ 50Pa, 160, 175

There was a second part of the audit that tells me my home's estimated energy use. I think the interesting thing was it said Heating, 33.6%; Cooling 20.33%; ...
Now that might not sound strange, until you realize I live in Phoenix. Heating is higher, I don't think so.

My house is single level, 2950 Sq. ft., 12 ft. ceilings. I have a natural gas water heater in the garage, and two split natural gas units in the attic. No basement.

Another funny part of the energy audit. They gave me maybe 10 of these CFL bulbs, and several pages of the audit went on to tell me how much great savings I will get by using these CFL bulbs. We'll it just so happens my job is related the the LED lighting industry, so almost every bulb in my house is an LED bulb, which can use LESS power than CFLs. They didn't seem to care about that.

Update: You got me thinking on this energy audit, so I went ahead and filed a complaint with the utility. I don't feel it was their fault, but if they are subsidizing these audits, they should get some feedback on the quality of the services offered. Who knows if anything will come of this.
 

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Old 04-26-13, 04:06 PM
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Well, the computer ate my first try, so here goes again. A bit shorter this time.
Your volume is 12 x 2950 = 34,400 ft³
Multiply your CFM50 by 60 to get: 60 x 2160 = 129,600 ft³ per hour. If we divide that by 20 (an estimate of the LBL#) we get an estimate of the natural leakage per hour, which = 6,480
If we divide your total cubic feet by that number we get: 34,400/6,480 = 5.3
That number is an estimate as to how often all of the air in your house is completely replaced on a day to day basis.

If you don't like the air in your house, wait 5 hours and it is all replaced. Of course it isn't a perfect process, but for a reasonably tight home, it illustrates that the air is still being replaced rather often.

Is your house considered tight, not really. I would call it just right for a small family that isn't generating a large amount of indoor pollutants. If you have a party with 30 people over smoking and passing gas, you will need to open a few windows. But day to day living should be just fine.

If we rebuilt your home with 8' ceilings it would probably have a very similar CFM50. Not that much air leaks out of the center of a wall. That would reduce your volume by 33% and equally reduce the time frame for total air replacement to about 3.6 hours. Since 3.5 hours is the old standard for being just right, you're good. It is the rate at which the air comes and goes that is important, not the volume of the home. A larger home just takes a little longer to find the same average concentrations on the inside.

Bud
 
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Old 04-27-13, 11:24 PM
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Bud9051 thanks for the calculations. Really this thread has gone in a bit different direction than I intended. I'm not overly concerned about the ventilation in my home. I did recently replace my HVAC units, and because a home energy audit said my home was sealed too tightly, and because I have a known radon problem, I had a ventilation port added that I could open or close with my home automation system. But really I added it so that I could take advantage of cooler temps at night to cool my house. I think it will save me money.

So is my air exchange good or bad, is the energy auditor I hired who is a ENERGY STAR Partner, Building Performance Institute (BPI) certified, and a Home Energy Rating System (HERS) rater full of it? I have no idea and I don't really care, because I have a CO2 sensor that can give me a pretty good idea of when I need to ventilate.

From what I see in my house, my CO2 runs in the upper 500's to 600's. That tells me that 800 is a perfect level to have the ventilation start. Since there is only two of us, CO2 seems to be pretty low. If we had a family of 6 or 8, I bet it would be much higher. So I learned that good ventilation for a home with two people, is probably completely different for a home with 8 people.

I've since spoken to several people (on another board) that do use CO2 sensors to control their ventilation. Like me, probably none of them HAVE to have ventilation, but its pretty neat to monitor. That's what I'm really looking for feedback on, the use of CO2 sensors to control ventilation.
 
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Old 04-28-13, 05:38 AM
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As to using Co2 as the trigger, my question would be, what are you trying to remove? Indoor air pollution has many components, fragrances, pollens, off gassing from materials, and others (not my best field), as well as Co2.

When you are away, in theory there should be no Co2 being added, but off gassing will have continued. In most cases, homes are simply equipped with a timer.

The other major source of Co2 is combustion and I'm assuming all of your combustion appliances are outside your conditioned space and vented well away. Candles, or non-vented gas appliances will be a source as well. When you operate your gas stove you should be running your exhaust fan as well. A non-vented gas fireplace is also not recommended.

Otherwise, you have the monitor and it does provide an opportunity to play, I do often, so I see nothing really wrong.

Bud
 
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Old 04-28-13, 10:46 PM
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In addition to the fun aspect, I'm hoping to detect that stuffy feeling if you have too many people in a closed up house. Id love to know about those other substances like fragrances, pollens, off gassing from materials, etc. but there isn't any good ways to detect those.

One other bad substance I have is radon. I bet a whole lot of people have this and don't know it. It is pretty rare in this neck of the woods, but all I know is I do have it. The EPA "acceptable" level is 4.0 pCi/L, my house had a level around 5 average, but with a radon mitigation system my level is down to around 2, better but not best. From what I've seen, further ventilation can lower this.

Unfortunately a stretch of near 100 degree days has kept me out of the attic, but i an planning to add a duct fan to each air intake. Currently with a damper only its less than ideal, because fresh air is only sucked in when the blower is going, and then it shares air with the returns. I should have the fans added if it cools a bit.

Two other things to think about. 1) If radon comes up from the ground, what other bad things might be coming up from the ground also? Do we really know? 2) Ventilating sounds great but it can cause a new problem; with fresh air comes lots of allergy stuff. I do have a better Filtrete air filter, but still this is a situation I'm monitoring.

To be continued....
 
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Old 04-29-13, 06:02 AM
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Yes, you could spend your whole life looking for things that might be hazardous to your health. Don't just restrict your efforts to things from the ground. Even a neutrino occasionally interact with a atom. That's gotta hurt if it's in your head. Then there is the odd cosmic ray that makes it through the atmosphere. Even worse if you fly. Oh, and meteorites, mosquitoes carrying Dengue and we each have a little bit of the above ground nuclear tests in us. The list could go on and on.
 
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Old 04-29-13, 12:36 PM
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I certainly don't disagree. But at the same time, unless there is a financial incentive for others to care about it, nobody does, and certainly the builder doesn't. They want to do things as cheaply as possible and move on.

Look at Radon. It is a known health risk, but if you look back many years, nobody even knew it existed, and we know this isn't a problem that just started. Even still, do most people even test for it? Of course not because there is no financial incentive for anyone (with the possible exception of your health insurance company) to care the least about your health. A few states do require testing when you sell a house, but only to prevent you from suing the former owner of the house for liability.

So the sad fact of our society is, you really have to look out for yourself because nobody else is going to unless there are public outcry and laws put in place. You find that for "fast" things like home fire regulation, but not things that slowly kill you over 30 or 40 years. So will there be some over reactions, absolutely. But that is your choice. The alternative is living with something like radon that is proven to increase cancer risk 100's of times over at some levels, and there is no question that millions of people are doing just that today.
 
 

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