Hi, folks! I've been lurking on this forum for some time without a membership because my Efficiency Kansas certification ran out years ago and I never pursued other certification. I haven't done a full energy audit myself in years, but I try to stay current with the field, so thank you for letting me lurk.

After doing a bunch of air sealing and insulation in my previous house in Kansas, I was concerned the house might be too tight, so I bought a uHoo air quality monitor (uhooair.com) which monitors temperature, humidity, air pressure, CO, CO2, TVOCs, particulates, NO2, and ozone. It found nothing interesting in that house (aside from raising a red alert when I once brought home a ripe cantaloupe!), so I had it in my in-laws' house for a year or so, but without any control over the situation there, I learned to ignore it.

When we moved to Omaha last year, I put the uHoo in the bedroom of our drafty 100-year-old apartment, and immediately it started freaking out about TVOCs and CO2 spiking each night when my wife and I and our two dogs would come into the bedroom. Whenever we would leave the room in the morning, these two factors would go back to baseline levels (below 400 ppb for TVOC and around 400 ppm for CO2). So we had met the enemy and it was us, but we figured when we moved to a house and had more space, that would resolve.

So we moved to our 95 year old house in June, and initially I put the uHoo in the finished attic because it smelled like dust and varnish to me up there, and I was curious about the particulates and VOCs. But it was unimpressed by the particulates; it continued to detect spikes in TVOC (as high as 1200 ppb) and CO2 (regularly 1000 but as high as 1800 ppm) every evening around the time my wife got home from work (I work from home) and every morning when we wake up, in spite of being sealed upstairs with no ductwork connecting it to downstairs.

I had a local energy auditor come and check the place over; he found plenty of air leakage and suggested that maybe the water heater was venting into the attic (brilliant!), so I had that checked out, but no, it is not. A friend suggested nocturnal animals might be living in the attic, but there's been no evidence to back that up. After a few more weeks of puzzling over the data from upstairs, I moved the uHoo to the living room, where I work during the day. Now it's showing high CO2 and sometimes TVOC all day long, as long as I'm in the house. As soon as all people leave the house, even if the dogs and cat are still here, the CO2 goes back toward baseline. If we go away for a weekend, the CO2 stays low until we return. The presence and absence of people in the house seems to be the one consistent factor in these readings.

Now, the alerts that I get from the monitor say I should open windows or add ventilation, but the energy auditor says the house is too leaky to benefit from ventilation and I should seal existing leaks first. I'm hesitant to seal any leaks when I'm already swimming in CO2. I've experimented with opening windows when it's not too hot out, but while that gets the CO2 under control, it lets in a ton of humidity that the AC won't remove unless I turn the thermostat way down.

I'm curious to know what you think about this situation. What am I missing?

Tags: air, carbon, dioxide, monitoring, quality

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I think you figured it out.

You exhale Co2 all day. The more people the higher it goes. I'm not sure what an unsafe level is? Take it with you in your car with 4 people, go on a short drive with windows up and a/c off. It should skyrocket up. 

Does your device read accurate? Maybe get another strict CO2 monitor to verify readings?

Your water heater puts out carbon monoxide. That is a different gas.

A water heater only puts out carbon monoxide if it's malfunctioning! When it's burning cleanly, it puts off CO2 and water vapor, but tests indicate those gases are going up the flue as they should.

I don't know if the device is accurate about the height of the peaks, but I know it's accurate about the baseline (400 ppm being the global average) and it consistently detects people coming and going from the house.

I would agree with Daniel's comments and question, is the device accurate. Over time sensors need to be tested and/or replaced. Utilize a dedicated gas sensor to compare results.

Not sure which house you were or are in that has the high CO2 levels at night in the attic. Perhaps zone testing needs to be done to evaluate the air leakage link between the house and the attic and other areas.

Consider using plants to help filter out some of the CO2 and introduce O2 in the environment. I believe NASA indicated in their research that Spider plants are effective filters.

Yes plants! great suggestion. 

Plants only take in CO2 when the sun is shining; at night they exhale CO2 just like we do. While adding plants might help me keep a clear head during the daytime, at night when the CO2 peaks are highest they would only add to the problem.

I think you could/should get some nice house plants around the house before you get too excited and start trying to drop coin on measures?

Thanks, I have house plants. Perhaps they are part of the problem, since they exhale CO2 at night and only take it in during the day when my wife is at work.

This is all based upon the assumption the data is correct. I have had a number of CO2 sensors go bad in my test equipment and in building occupancy controls. If it's that important to you, verify the sensor. Just remember though, being able to breathe easy will never come from a gadget. Wink.

Do you sleep with your bedroom door open or closed?  Is there a return air register in the room?  Does the furnace fan run continuously?  There was great article on Green Building Advisor about this phenomenon a few months ago.

Door open. No return register in the room. No, the air handler only runs when the AC is on.

It is natural to have an increase in CO2 at night due to occupancy of any residence. I would recommend, that if you are concerned about these readings you could install an ERV or HRV in line with your existing duct work (this presumes you have forced air in the home). with either choice, you would be exchanging your poor IAQ (indoor air quality) with the fresh air from outside.

I am curious to know what your blower door number was in correlation to the size of your home, as well as what you currently have for mechanical ventilation of your house.

Another option would be to install a continuous run fan to pull air out of the home and force infiltration into the home. This option is functional, but you miss out on regaining the heat/energy you put into the home.

Keep in mind that stack effect on a home changes throughout the day. Wind speed, temperature, air pressure etc.. all play a part in to how your home will breath.

I don't have the blower door number handy, but he said it was about 3x the guideline, which is why I characterized the house as "leaky."

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