Mikesm
New Member
Hi everyone. I have a strange problem that strange problem that I'm seeking help with.
We built a new house in the SF Bay Area with a full basement and moved in back in 2019. It's a very tight house and very energy efficient. We have 2 parents and 4 kids, and even through with have 2 ERV's, sometimes it still feels stuffy. I got some of the consumer air quality sensors that measure CO2, and found levels in the house can often hit 1500 ppm or more if the windows are all closed. Based on the HVAC system and ERV flows, this should not be happening with just 6 people living in the house.
So I took one of the consumer sensors around to each room looking to see if there was some kind of CO2 emitter adding to the people's normal CO2 exhaling. The basement mechanical room had much higher levels, and especially high levels right above the sewer ejector pump. The contractor doesn't think there is a leak in the pipes to the ejector, because we can't smell any foul odor at all, and if a pipe were cracked, that it would smell to high heaven. Nothing obvious is visible.
To get a better feel for CO2 levels, I wanted to put a sensor in the mechanical room, but the normal CO2 sensors you can buy have to calibrate periodically by being exposed to outside air (about 400 ppm), and will not be accurate if that doesn't happen. Also, they don't report levels past a certain point. Since I am an engineer, I rigged a microcontroller with a Telaire T6615 CO2 sensor, and placed it right on top of the metal plate that covers the hole where the ejector pump is located, near the cutouts for the pipes going to the pump. This sensor has an internal gas reservoir for calibration, so doesn't need to be exposed to fresh air, and can read very high concentrations of CO2, and reports every minute to a computer that logs the CO2 value the sensor is seeing.
Here is a graph of the last few days:
As you can see, there are VERY high CO2 levels involved. The USDA says numbers around 40,000 PPM are immediately harmful to life. It doesn't appear to be a lot of CO2 being released because higher up in the room itself don't go above 8000 ppm, and in the basement much over 2000. It appears to be diffusing through the house from the mech room area. This can happen faster when the make up air is triggered, because the make up air inlet is in that room. There seems to be a pattern where the CO2 level starts going up before noon, and peaks around 6 or 7 PM and then drops off most days.
Now, it doesn't appear to be correlated to ejector pump use - even before summer break, the house did not have more than one or 2 people at home during the hours when the CO2 release was highest. And the last 2 days of that graph, noone has been home because we're on vacation.,
There is an HTP phoenix hot water heater in the room, but if the exhaust vent was leaking, the CO alarms would be going off, and I did shut the hot water heater off before we left on vacation, and I have shut it off during the day before without any effect on CO2 emissions. There are also 3 air handlers for Mitsubishi heat pumps there, and they too have been shut off for the last 2 days, and I can't figure out how they could be causing this problem either.
So this brings us back to the ejector pump. Some folks have speculated that it could be a lot of organic material decomposing under the foundation with the CO2 trapped under the house, and merely seeping up around the hole where the ejector pump installed in. But if that were the case, I would expect that CO2 emission to be continuous, and not in this pattern we see from the sensor.
No one seems to understand what is causing this. Does anyone here have any ideas as to how an ejector pump might be releasing CO2 into the house? Any other explanations I should be looking at?
Thx
Mike
There is an HTP Phoenix hot water heater there
We built a new house in the SF Bay Area with a full basement and moved in back in 2019. It's a very tight house and very energy efficient. We have 2 parents and 4 kids, and even through with have 2 ERV's, sometimes it still feels stuffy. I got some of the consumer air quality sensors that measure CO2, and found levels in the house can often hit 1500 ppm or more if the windows are all closed. Based on the HVAC system and ERV flows, this should not be happening with just 6 people living in the house.
So I took one of the consumer sensors around to each room looking to see if there was some kind of CO2 emitter adding to the people's normal CO2 exhaling. The basement mechanical room had much higher levels, and especially high levels right above the sewer ejector pump. The contractor doesn't think there is a leak in the pipes to the ejector, because we can't smell any foul odor at all, and if a pipe were cracked, that it would smell to high heaven. Nothing obvious is visible.
To get a better feel for CO2 levels, I wanted to put a sensor in the mechanical room, but the normal CO2 sensors you can buy have to calibrate periodically by being exposed to outside air (about 400 ppm), and will not be accurate if that doesn't happen. Also, they don't report levels past a certain point. Since I am an engineer, I rigged a microcontroller with a Telaire T6615 CO2 sensor, and placed it right on top of the metal plate that covers the hole where the ejector pump is located, near the cutouts for the pipes going to the pump. This sensor has an internal gas reservoir for calibration, so doesn't need to be exposed to fresh air, and can read very high concentrations of CO2, and reports every minute to a computer that logs the CO2 value the sensor is seeing.
Here is a graph of the last few days:
As you can see, there are VERY high CO2 levels involved. The USDA says numbers around 40,000 PPM are immediately harmful to life. It doesn't appear to be a lot of CO2 being released because higher up in the room itself don't go above 8000 ppm, and in the basement much over 2000. It appears to be diffusing through the house from the mech room area. This can happen faster when the make up air is triggered, because the make up air inlet is in that room. There seems to be a pattern where the CO2 level starts going up before noon, and peaks around 6 or 7 PM and then drops off most days.
Now, it doesn't appear to be correlated to ejector pump use - even before summer break, the house did not have more than one or 2 people at home during the hours when the CO2 release was highest. And the last 2 days of that graph, noone has been home because we're on vacation.,
There is an HTP phoenix hot water heater in the room, but if the exhaust vent was leaking, the CO alarms would be going off, and I did shut the hot water heater off before we left on vacation, and I have shut it off during the day before without any effect on CO2 emissions. There are also 3 air handlers for Mitsubishi heat pumps there, and they too have been shut off for the last 2 days, and I can't figure out how they could be causing this problem either.
So this brings us back to the ejector pump. Some folks have speculated that it could be a lot of organic material decomposing under the foundation with the CO2 trapped under the house, and merely seeping up around the hole where the ejector pump installed in. But if that were the case, I would expect that CO2 emission to be continuous, and not in this pattern we see from the sensor.
No one seems to understand what is causing this. Does anyone here have any ideas as to how an ejector pump might be releasing CO2 into the house? Any other explanations I should be looking at?
Thx
Mike
There is an HTP Phoenix hot water heater there
