High CO2 Levels in Bedrooms
Hi there, I recently purchased and installed the new Panasonic Intellibalance 200 FEC in my 2015 built home as a retrofit, using the return air plenum method. I have been running the unit on max to test for the last week and while CO2 levels are low in the house proper (big improvement since I found a hidden damper under overlapping flexible duct insulation that had completely shut off my fresh air intake for the last 7 years), the bedrooms are still a problem at night. I am seeing over 1000ppm at times and this is something we’d like to get as close to baseline as possible. I installed the unit myself and I believe everything was done correctly. The only thing is the existing holes in the air return from where the previous 0% efficient ventilation fan was located were more like 35 inches instead of 40 inches apart which is the recommended distance. I’m doing some tests – closing vents elsewhere in the house to get more air through the bedroom vents, trying opening the bedroom door a bit at night(though I don’t think that will be sustainable for other reasons), and considering other options.
We live in northern Canada (Edmonton, Alberta). If I wanted to get the freshest air possible in our bedrooms, what could we do? I know that a through wall fan is an option, as well as ductless ERV and maybe a dedicated ducted Intellibalance 100 with lines running to and from the bedrooms in the attic even?) Or maybe running a supply line off the Intelli-Balance 200 and connecting it directly to the ducts that run to each of the bedrooms, if I can determine which they are? It does get to -40C/F here occasionally, and -20C pretty commonly in the winter.
By the way, I’m measuring CO2 with the accurate Aranet 4.
Thanks in advance for your help!
Here’s a pic of the Panasonic IntelliBalance 200 for no particular reason :). I went insulated duct all the way around in case it helped with sound and it is completely silent running at full 200cfm.
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Replies
It sounds like your ERV is ducted into the furnace return? Perhaps if you have an ECM air handler fan you could boost the fan speed (there are often dipswitches to adjust). Look into door cutouts to allow more transfer air from the bedrooms. (probably worth taking differential pressure reading first to see if it's worthwhile with the door shut).
You could try disconnecting the exhaust between the AHU and ERV and letting it draw from the mech room temporarily to see if it affects the readings (if you think short cycling between the intake and return is an issue).
Hi Josh, thanks for the message. I had just started reading about the dipswitches when you made this post and that reinforced it. I read my Lennox EL296V manual and found the dipswitches are default set to run the continuous fan at 38% speed. I flipped the dipswitches to generate 100% fan speed as a test. Given all our bedrooms have supply and returns, this is having a great impact. Now our master bedroom does not go above 700ppm CO2 at night with two adults sleeping in it. Fantastic!
I'm interested in opinions/evidence as to CO2 ppm, personally, I'm not too concerned with nighttime peaks of about 1250 ppm CO2 (two humans and 1 large dog), though if it was 2000 ppm and didn't drop to below 1000 ppm during the day, I'd start looking to step up ventilation.
OSHA has an 8 hour limit of 5000 ppm CO2 and many people work in relatively high CO2 environments, within OSHA limits (<5000). A green balance between interior CO2 and tightness, especially in cold climates, may possibly aim for a daily average of 1000 ppm (e.g., with peak max less than 2000 ppm CO2).
Studies are mixed and differences exist depending on task (while awake). One study had 24 people, another 30 people, . . . subjective assessments may be questionable with such small study sizes. Is there some effect in the range 1000 ppm to 2000 ppm, I think the data tend toward "yes", but that effect is likely small. A "significant" difference, statistically, does not necessarily mean a "significant" impact. For example, a drop in task completion from 95% to 92% can be "significant" for two different CO2 levels, however, that does not mean, in ordinary parlance, such a drop is "significant" (or even "substantial").
A review article:
Environment International Volume 121, Part 1, December 2018, Pages 51-56
"Effects of low-level inhalation exposure to carbon dioxide in indoor environments: A short review on human health and psychomotor performance"
https://www.sciencedirect.com/science/article/pii/S0160412018312807
"Thirty male active commercial airline pilots performed three 3-h flight simulations on the flight deck at 700, 1500, 2500 ppm CO2. The concentration of CO2 was modified by introducing ultra-pure CO2 into the simulator, and the ventilation rates remained the same for each test. The in-flight performance at 2500 ppm CO2 was significantly lower than that at 1500 ppm and 700 ppm. The difference in flight performance at 700 ppm and 1500 ppm was not statistically significant; however, the pilots were more likely to successfully perform five of the seven most difficult maneuvers [out of 21 total manuevers] at the lower CO2 concentration (Allen et al., 2018)."
Allen et al.: https://www.nature.com/articles/s41370-018-0055-8
If pilots are doing OK at 1500 ppm CO2, not sure sleeping with a peak at 1500 ppm CO2 is going to make much of a difference - though I may be wrong. NIST has some data on this issue too, mainly for inhaling what others exhale.
Exactly what I was thinking as well.
I like to read in bed which I would not call the most cognitively challenging task. If anything a bit higher CO2 level helps with going to sleep, so in a way it is a good thing. Maybe if you use a bed as a home office, better ventilation is needed.
My definition of good bedroom IAQ is that when I walk back into the bedroom in the morning the air does not smell stale. Not the most scientific definition.
Excessive of ventilation comes with a big energy penalty and cost. You need to pay to condition the fresh air supplied by the ERV plus to run all the fans. A furnace blower on full can easily suck 250W to 500W. 24h/day that quickly adds up.
Maybe somebody will do a detailed study on this, and there's nothing quite like the "sniff" test. If the dog could talk, wonder if there's an IAQ sniffing dog?
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