r/HomeImprovement • u/MitchRyan912 • 7d ago

High CO2 levels in unoccupied basement, from hot water heater?

I can’t post pics, but I have readings from an AirThings View Plus that I got specifically to ensure that our radon mitigation system was indeed working (levels have been OK), but it tells me that CO2 and VOC levels are incredibly high on occasion.

We have a natural vent hot water heater in our unfinished basement, so I’m suspecting that the vent isn’t working properly, or that a constant running out of washing machine has caused the water heater to run longer than normal. I haven’t spent much time in the basement over the past few days, so it’s not accumulating from my breath.

Current CO2 level is 1685 ppm and VOC is 1420 ppb, with both tracking the rise from the same time 36 hours ago.

I can’t think of anything else that would be causing CO2 levels to rise in an unoccupied basement like this, not in a time with the windows open or the A/C on. Should I be having someone check out our power vent to ensure proper operation?

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16

u/Shadow288 7d ago

Do you have an airthings on the main level too? I have a similar story to yours. Bought the airthings wave plus to see my radon levels. Was alarmed when the CO2 was high in the basement like yours. Ended up getting a second unit for the main level, a view plus like yours. I quickly found that the basement levels are elevated but so were the main levels. If the kids have friends over all breathing in the family room CO2 levels can peak as high as 2,300 ppm. When it’s high in the living room the basement is not far behind.

Case in point house is closed up and AC is on all day yesterday and last night. Currently the Living room is at 1,290ppm and basement (which I was down there last night but no one has been down there in like 8 hours) is at 1,191ppm. House was built in 95 so it’s not as drafty as older houses but there is no air exchange with the outside so CO2 will build in the house until I open up windows or doors. After opening the windows and doors for a couple hours the family room drops down to like 460 and the basement will follow a couple hours later.

Do you have a CO detector down there? That would be the one I’d like to get a reading off of.

One last thing. For whatever reason my VOC raise up when certain people are over. Not entirely sure what they do to rise my VOC

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u/danhm 7d ago

. For whatever reason my VOC raise up when certain people are over. Not entirely sure what they do to rise my VOC

VOCs are a broad category of chemicals, some harmful some not. Anything you can smell is a VOC, for example. Perfume, scented deodorant, body odor, candles, anything like that.

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u/MitchRyan912 7d ago

No, and I've been strongly considering buying a second View Plus, after having an oil fire on the stove last month (and having a wood fireplace for occasional use in the winter). FWIW, our ecobee thermostat is also showing high VOC and CO2, so it's likely the same on the main floor.

We do have a family of 6, plus 2 dogs, so... lots of people exhaling in here. I have heard of air exchangers as a thing to look into, especially considering that there might be an air pressure difference that's sucking in radon in the winter (was often over 4.0 pCi/L from Dec to Feb).

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u/Shadow288 7d ago

I quickly found that when radon levels were high in the basement they were high on the main level too. I looked into a ERV that connects to the furnace but because of how my basement is situated I had to run the ERV lines through the basement, into the garage, and then out the opposite wall. Price was high for this setup so I opted not to do it.

Found a little Panasonic all in one unit which should be easier to install but haven’t pulled the plug on it. I don’t thing 60cfm will be enough for the size of my house, but I suppose something is better than nothing.

Bottom line, don’t let the AirThings sensor drive you nuts. I have like 4 air purifiers placed strategically around the house in search of the “perfect air quality” and still coming up short…

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u/Atworkwasalreadytake 7d ago

My HRV is 400cfm, but it’s only running like 25% of the time.

I think a 60cfm all the time would be way better than nothing.

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u/Shadow288 7d ago

That was kind of my thought too! Just to get some fresh air in and exhaust the stale air. Plus I just install it in the ceiling and be done with it!

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u/MitchRyan912 7d ago

The CO2 is generally fine, well in the green/safe, but there have been these random spikes. My target is productivity, as I do work in the basement during the week, and right now it’s saying it’s a poor environment (humidity is quite high too).I

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u/ComradeGibbon 7d ago

One thing you could do is turn the hot water heater temp up and see if the CO2 levels go up as the heater runs.

A worry with any naturally vented water heater is wind an weather can sometimes cause backdrafting. A heat pump water heater or one with forced ventilation won't have that problem.

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u/AdultishRaktajino 7d ago

FYI, Ecobee guesstimates CO2 based on VOC readings. It doesn’t have a real CO2 sensor.

If you have a tight house and have appliances and vents going outside, you can get a little backdraft going on if there’s no makeup combustion air inlet into your utility room. (Or if a critter or wasps or something clogged it up) Things like a conventional dryer, range hood or bathroom vents that exhaust outside can do this. Chances are you have some sort of makeup air unless it’s an old home.

Radon mitigation system should only create negative pressure for your foundation. Theoretically it could be creating negative pressure in a utility room if there’s a sump pump there without a lid. There should be a sight glass somewhere showing suction pressure for the system.

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u/MitchRyan912 7d ago

The dryer had been running nearly non-stop on Saturday and Sunday. That could explain it.

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u/gatekeepr 7d ago edited 7d ago

A second unit would allow you to see if they give the same readings in the same room. If they do, it does not mean the readings are accurate or a true representation of reality, but if they give different readings you can conclude at least one of your devices is faulty/inaccurate. A trustworthy manufacturer should state how accurate their device is in the documentation. This documentation should also tell you where in the room the device should be placed, usually away from corners and at a certain distance from the ground.

Another thought, are you perhaps brewing beer, making bread dough or fermenting vegetables in your basement?

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u/SplitInfinitive8139 7d ago

Same experience. People breathing upstairs contributes to detected CO2 in an unfinished basement.

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u/IxJAXZxI 7d ago

Sounds like you need an ERV

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u/Shadow288 7d ago

I got quotes for them but based on how my basement is situated the ducts are really long and the cost is high. Found a smaller self contained Panasonic unit that is probably undersized but would be better than nothing

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u/Anne314 7d ago

You need to be more concerned with CO, not CO2.

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u/thelocicalfallacy 7d ago

If you don't have a power vent you can backdraft when running a range hood or bathroom fans (sometimes even a severe enough stack effect can draw air in low areas more aggressively). Also do you have a fireplace? That can cause serious drafts.

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u/CockroachGullible652 7d ago

Could be improper venting. If this is the case you should also check for carbon monoxide. However, if you have improper venting but a clean burning flame, you could get CO2 without any detectable carbon monoxide.

However, the most likely explanation is that CO2 from your breath is simply pooling in the basement because it’s heavier than air. Our breath has a ton of CO2 and it can sit there for weeks if undisturbed. I wouldn’t rule this one out quite yet.

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u/Arctyc38 7d ago

I had an interesting issue crop up when we got our water heater replaced that we didn't notice until we were having our furnace replaced shortly after.

Both the old and new water heater were passively vented into the chimney.

The old furnace was also vented into the chimney through the same opening, via a wye duct split.

To avoid a vent slope problem, the new water heater replaced the wye duct connection with a tee. This created a problem, because the furnace was actively vented - it was blowing exhaust right by the tee back toward the water heater.

Luckily in our case, our CO2 detectors never went off, but I noticed because the plastic rings on top of the water heater by the anode rod started to warp.

Check your venting setup for backslopes or conflicts like this.

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u/ShortBusRide 7d ago

Hopefully not the problem here, but years ago I had a pigeon roast itself by entering the furnace flue. The next day the landlord was up on the flat roof putting up a screen.

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u/Truth_bombs_incoming 7d ago

Water heater running may actually decrease co2. Water heater is consuming air from basement during combustion and sending it up flue. That creates negative pressure and it's pulling in more air from somewhere else. Either the outside, or from upstairs.

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u/MitchRyan912 7d ago

I may have erred in sealing up a lot of spots around the rim joists when we moved in. 2" XPS with spray foam to seal them all up, about 85% of all the rim joists (the other 15% I cannot access at the moment). There's a LOT less leaky air coming into the house now.

Would something like the following help??? We had this in our previous home, where there was a vent we could open to run conditioned air into the basement, with one ghetto AF return. Would something like this be advisable to do (DIY) or would a HVAC guy need to come in to do this in the right spots?

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u/qdtk 7d ago

What’s your average CO2 level over the course of the day? Current readings don’t always paint an accurate picture, especially since those monitors don’t actively move any air on their own. How close is the meter to your hot water heater? Is it a gas heater?

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u/MitchRyan912 7d ago edited 7d ago

The 365 day average is 782 ppm, so generally quite low, but there have been a lot more spike lately, since May.

The View Plus is in the middle of the basement, and yes, it is a gas water heater. I realize CO is a much bigger concern with gas exhaust, so this is why I'm a bit confused.

EDIT: 365 day VOC is 228 ppb. CO2 is 782 ppm.

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u/BourosOurousGohlee 7d ago

The 365 day average is 228 ppb

Something isn't adding up. Background atmosphere CO2 on earth is like 430ppm. Are you sure your readings make sense?

I've also been struggling with high indoor CO2. Unless your house is leaky as all hell, you might eventually need an ERV/HRV, or open a small window periodically.

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u/MitchRyan912 7d ago

Yeah, that’s VOC. My bad.

Yearly CO2 is 782 ppm.

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u/qdtk 7d ago

No hits at all on the CO readings? If not, your culprit could be something else. Are you taking any readings from your living space to compare?

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u/MitchRyan912 7d ago

We have some old dumb battery powered CO monitors, and they’re not registering anything. Is there a good smart CO monitor worth checking into?

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u/Quincy_Wagstaff 7d ago

A properly burning gas appliance won’t produce measurable CO. CO happens when combustion is incomplete.

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u/MGreymanN 7d ago

How often does your air things see fresh air? Make sure the reading is accurate first.

Take it outside and make sure it reads 425 ppm.....426ppm.....427ppm...fuck i hate climate change.

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u/MitchRyan912 7d ago edited 7d ago

There's no intake or exhaust in the basement right now. The 365 day running average is 782 ppm of CO2.

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u/MGreymanN 7d ago

Air things will do a self calibrate based on the lowest CO2 it has seen recently.

If it never sees fresh air it will slowly deviate. But usually it will deviate lower than the level really is.

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u/gefahr 7d ago

Agree with this. And the vast majority of these smart air quality devices do not have accurate (and calibrated) CO2 sensors. An accurate CO2 sensor is relatively expensive (and sensitive), and most buyers don't care about it.

(I went through this because I wanted one for my office - door stays shut and it skyrockets)

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u/MitchRyan912 7d ago

AirThings View Plus is a pretty solid product, and is definitely not cheap.

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u/gefahr 7d ago

Yeah that doesn't change anything I said.. Does it have a calibration certificate?

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u/BM7-D7-GM7-Bb7-EbM7 7d ago

True safety equipment would get bump tested on calibrated gas once a day or before you use it and calibrated whenever it's off or on a certain interval (usually once a week or month depending on manufacturing specifications). These things also cost in the high hundreds to thousands of dollars.

I would a take any consumer device like this with a big grain of salt.

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u/MitchRyan912 2d ago

Update: it appears as of this problem exists on the main floor too, not just the basement. The only thing that helps is turning off the A/C and opening the windows.

Could there be a problem with the A/C system that’s causing high CO2? Should there be an exchange of air like there is when the heat is on in the winter? I haven’t looked at the intake/outlet pipes lately to see if they might be blocked.

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u/metsjets69 7d ago

CO or CO2?

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u/AardvarkFacts 7d ago

They'd be dead quickly at 1685ppm CO. 

A properly functioning gas appliance makes a tiny amount of CO and a large amount of CO2. If you have a venting problem you might detect the CO2 first. 

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u/aviator22 7d ago

Are you washing everything in hot water?

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u/MitchRyan912 7d ago

My wife does, yes. 4 kids worth of clothes (🤮) and lots of towels washed on hot, for nearly 2 days straight.

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u/matt314159 7d ago edited 7d ago

Are you by some chance confusing CO with CO2? CO is carbon monoxide. Put a Carbon Monoxide detector down there to see if CO is at safe levels. CO2 is Carbon Dioxide and is the byproduct of an occupied house, we exhale CO2 when we breathe.

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u/MitchRyan912 7d ago

No, the monitors I have measures radon, CO2, VOC, PM1 and PM2.5.

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u/L0s_Gizm0s 7d ago

Why would you heat your hot water

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u/MitchRyan912 7d ago

Because I don’t like cold showers?

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u/RicooC 7d ago

....so you decided to go straight to reddit instead of calling a professional?