Awair Air Quality Monitor vs. ERV
Hello GBA friends,
I’ve just had an ERV installed on the second floor of my 2BR, 1 1/2 story, 1934 Boston-area house.
Prior to this installation, there was only one exhaust vent in the house and that is for the “fan in a can” that provides exhaust for my gas furnace. So there was no exhaust for the bathroom prior to the ERV installation.
Now the ERV is installed and I was hoping that it would not only provide needed humidity control from the second floor bathroom, but would also provide some healthy ventilation to the two bedrooms.
However, my Awair Element air quality monitor is showing that the ERV isn’t helping much with CO2 and VOCs.
Am I operating the ERV properly?
Is it wrong for me to expect the ERV to improve air quality?
Was the installation done wrong?
Is the Awair Element providing bad advice on what good CO2 levels are?
The make and model of the ERV is Renewaire EV90.
Back in October 2021, before the ERV was installed, the Awair Element was showing CO2 levels at night at around 1200 ppm. Now, with the ERV installed and operating at the 10% run option, the CO2 levels at night are 1000 ppm. But the Awair recommends CO2 levels below 600 ppm.
The exhaust duct is located in the bathroom above the door. There are two fresh air ducts, located above the doors in the bedrooms, just 9 feet away from the exhaust duct. We also have ASHP cassettes that are pointed at the doors in the bedrooms.
I wasn’t really looking for a super expensive way to exhaust the bathroom. Really, I was hoping to improve air quality!
Thanks in advance for your help!
Best wishes, Kris in Arlington, MA
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Is this a balanced system? Was it commissioned or just turned on? Does it have a boost mode?
The system is balanced and it does not have a boost mode.
I’m not sure what the difference is between commissioned or turned on. I asked the installed this and did not get a response.
What do you think?
Best wishes, Kris
10% run on a 90CFM unit is not a lot.
You want around 20CFM in each bedroom, so that would be around 50% run or 100% at low flow. Generally running the unit at lower flow rate and longer duty cycle improves efficiency of the ERV.
The EV90 is only really a 90CFM unit when running 100% of the time and at 0.2" of pressure. At 0.4" (seemingly a typical level), the airflow is 68CFM total. It's also a single-speed unit with no high/low speed modes (and thus ability to influence airflow and/or noise).
Did your installer measure the actual pressure drop and look up the airflow for the unit as installed? There's a table in the manual you use to see what it's actually putting out.
Either way - since it's likely not running at the full 90CFM, your unit likely needs to run 100% of the time to deliver the ventilation that your space needs.
Aren't ERV's supposed to be on all the time anyway? It's flow rate that you adjust, not duty cycle.