High CO2 levels with Ventilating Dehumidifier
Hey Everyone,
We recently completed a second-story addition to our home, which included a replacement of mechanicals for the existing living space. Throughout the living space, we have been challenged to keep our CO2 levels under control.
The home is 2,640 sqft and is located in Central Florida. 4 occupants, no pets, no smokers, and no combustion appliances or candle burning.
We have two Ultra-Aire 70H dehumidifiers with fresh air intakes, one for the upstairs system, and the second for the downstairs. Both have a DEH3000 control and are normally set to a 30-30 open/closed vent cycle. Recently, I have been changing it so the “vent” is set to open all the time.
We had a duct design, and recently just had the system balanced to ensure we were getting the intended CFM throughout the home. At least our higher levels are consistent from area to area if that’s a positive at all.
Today I broke down and opened up some windows, forced the bath fans on, and am hoping to drop it a bit, but I know it will creep back up.
My wife is saying that I sealed the house too well. Which, while a good thing, is now possibly proving to create other challenges.
I have changed both filters on the dehumidifiers and ensured there isn’t anything restricting the intakes.
Any ideas on what we should check? Or am I overreacting to the CO2 levels?
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Replies
Here is a month-long view of the CO2 levels to show this isn't an issue that sprang up recently, we have been a bit challenged all along. You can tell the periods when we were away during Thanksgiving as it dropped.
What is your blower door ACH50? Also, why ventilated dehumidifier (supply only) without an exhaust plan? It doesn't seem balanced right now unless you are also running exhaust fans at some frequency.
No solutions here. FWIW I'm seeing the same issues with a ventilating dehumidifier approach (return to return, HVAC system runs all of the time). I'm not 100% certain about the calibration of my CO2 meter, so I'm sorting that out before addressing things further.
If I understand correctly, the Ultra-Aire provides fresh air with the ~6" tube with a motorized damper. But is there a separate fan moving the outside air in? Or is the design that the outside air will "slip-stream" in (ie the fan will pull less from the return when supplying outside air)? Have you been able to confirm that fresh air is coming in? How are your Ultra-Aire's ducted? (Independent? Supply, Return etc?)
https://www.santa-fe-products.com/wp-content/uploads/2023/06/6_23_Ultra98-120-Manual.pdf
Do people with balanced ERV achieve consistent CO2 ratings below 1000 ppm?
Seems your dehumid is trying to bring in air, but without equal exhaust, it can't really do that, especially in a tight house.
If you can, consider setting up a Hubitat or other smart home system that will turn on your exhaust fans when your dehumidifier brings in fresh air.
In the meantime, just turn on an exhaust at all times the dehumidifier fresh air intake runs and see if that helps.
Did you take CO2 readings before installing the dehumidifiers?
Did you have a blower door test done? A lot of times people come here and say they have "tight" houses, but when we see the blower door numbers they're really only average or worse.
Thank you for all of the help! Our ACH50 is 1.93 post construction. Prior it was 3.64.
I have set the exhaust fans to run at intervals every hour for 30 min. This has helped tremendously.
Our CO2 readings are now consistently below 700, and we feel generally "better" in the house, even if it is all psychosomatic.
I'm thinking we may need to evaluate an exhaust plan. Or at minimum, just tie a exhaust fan in with the damper for the dehumidifier fresh air intake and have it trigger when the damper opens.