CO sensor accuracy, placement, risks.
July 25, 2014 8:43 AM   Subscribe

I'm moving for the first time into a house with gas (stove and heat) and I'm completely terrified that my two small children are going to die of CO poisoning. Please help me understand sensors, risks, what to look for and such to help alleviate my paranoia.

So I read this thread and it only increased my fears. I bought this sensor, but how do I know if it works? I've heard that some of them aren't very reliable. How do I assess the numbers? What do I do if the numbers go up? Do I need more than one sensor in different rooms? Does it matter if I put it high or low on the wall? If I seem paranoid, it's because I am. Not so much for myself, but I've got two tiny children who are way more vulnerable than I am. Tell me everything you know about CO sensors, risks, etcetera!
posted by celtalitha to Home & Garden (16 answers total) 2 users marked this as a favorite
I have the exact same sensor. In the living room about eye-high. But that's where the gas fireplace is. I also have a different sensor in the bedroom plugged in to a power outlet, and two different battery powered combination CO and smoke/fire detectors. One in the room with the furnace and one in the main hallway. Basically REDUNDANCY is the key to assurance.

ps. I am not paranoid about CO, but the fire department made recommendations about 1 on each level of the house and 1 outside each sleeping area.
posted by Gungho at 8:53 AM on July 25, 2014

Nearly everybody in the UK has gas for heat, and CO poisoning is still unusual enough that most people don't own a CO detector even though they are cheap as chips. Not that I suggest you shouldn't get one; just mentioning it in case it helps calibrate your stress-o-meter!

What's much more common (and required by law here in rental properties) is an annual boiler service. Whenever I hear about a CO poisoning case it's someone with an old and badly maintained boiler. If there's some registration body for gas fitters where you are, then check the registration of whoever does your service.
posted by emilyw at 9:10 AM on July 25, 2014 [2 favorites]

Handling CO output from your oven/stove is simple: you don't run it all the time and when you do, you can always crack a window a little if you want fresh air. The burners in your cooking appliances are efficient enough that the CO produced is minimal.

So the real question is your furnace (or boiler, since emilyw mentioned it and you didn't say) and/or water heater if it's gas.

A properly equipped furnace technician can inspect the system and run a flue gas output test. That will tell you the mix of gases coming out of the furnace and up the chimney.

The last part is important, since your heating system DOES produce CO, but it always should go out the chimney and never into the house. What will cause CO to get into your home will be a blocked flue or a defective heating system that is leaking combustion gases into the ventilation system.

So for your peace of mind, just schedule a HVAC inspection/cleaning and have the tech give you a written report. That will go a long way to help you (and the kids) sleep better.
posted by JoeZydeco at 9:29 AM on July 25, 2014 [2 favorites]

In terms of finding out whether all your appliances are in good working order, I know that my state has a free/reduced rate home energy audit program. Among the things they did at ours was check that ventilation was working as expected, confirming that there were no gas leaks or significant sources of exhaust inside, and talk with us about smoke and CO detector placement. Perhaps your state has the same? It was really helpful for me to learn more about our home and where our priorities were, and it might put your mind at ease.

For detector placement, the density of CO is very close to that of air, and I wouldn't expect it to either settle or go upwards in a typical home. At our audit they recommended having enough CO detectors in the house to hear them when they went off, and not too close to any spot where they'd get dusty/oil-spattered. We've got a small house so for us it's just the one.
posted by tchemgrrl at 9:53 AM on July 25, 2014

Gas in the US doesn't contain CO. When natural gas burns in open air, that means there's plenty of oxygen, and it combusts completely. CO production is negligible.

That's the case with your stovetop and your oven, and your furnace. You don't need to worry.
posted by Chocolate Pickle at 9:58 AM on July 25, 2014

Response by poster: Chocolate Pickle, considering there have been cases of in-home CO poisoning in my state, I don't think that's correct.

The boiler is in an outside-attached laundry room, so I'm more concerned with potential gas leaks from the stove. So should I put the sensor in the kitchen closest to the oven, or in a bedroom? It's a small house, about 700'.
posted by celtalitha at 10:07 AM on July 25, 2014

Response by poster: On further research it seems the potential for a stove gas leak to reach dangerous levels is pretty ridiculously minimal. My paranoia is slightly reduced...
posted by celtalitha at 10:12 AM on July 25, 2014

A few years ago, we had a craptastically cheap CO detector in a rental house. Our landlord decided to run a woodchipper next to our house, and she aimed the exhaust pipe at our window. I didn't realize she was pumping CO into our damned kitchen, so I was doing kitchen chores. The bargain-bin CO detector went off, eventually firefighters were at our house with gigantic fans, and so forth.

The moral of the story is, I was the only one who got any level of real CO sickness, because the pipe was aimed right at me, and the CO detector was across the kitchen from the window. I threw up a few times. Doctor checked me out, told me to take it easy for a while. My husband, roommate, and cats were fine. So our crappy CO detector (which was far less fancy than yours) went off when CO was present. As it was supposed to. I would suspect that your CO detector has to be better than the one we had. Ever since, though, I keep around good CO detectors.

The firefighters had a good time yelling at my landlord, by the way.
posted by Coatlicue at 10:13 AM on July 25, 2014 [2 favorites]

What Chocolate Pickle was trying to say was that natural gas is made of methane (CH3), and does not contain any carbon monoxide by it's nature. You could develop CO as a by-product of inefficiently burning the methane.

So your question about a gas leak is something entirely different than CO poisoning. Natural gas leaks are a hazard too, and there are methane sensors you can hang in your house to detect this as well. But you also carry a free gas detector with you too - your nose. A very pungent odorant is added to natural gas to warn you there is a leak and even a very small amount will be noticable. You can even run the stove for a second without lighting it and try it yourself and get familiar with the scent. It won't hurt you!
posted by JoeZydeco at 10:17 AM on July 25, 2014 [2 favorites]

Also, with regard to stove gas leaks, natural gas in the US is mixed with a noxious smelling compound (some states use mercaptan, for example) so you know when there's a leak. It smells so bad that I detected a leak outside on our street in very windy weather. Turns out there was a teeny tiny itty bitty gap in one of the lines under the street.
posted by cooker girl at 10:20 AM on July 25, 2014

it seems the potential for a stove gas leak to reach dangerous levels is pretty ridiculously minimal

That's semi-true.

If you are not right there to smell it, a gas leak can build up to levels that can be ignited by a spark, although you will not die of breathing the stuff. This can be dangerous.

Depending on your stove, a gas leak can happen if a burner is blown out or if someone knocks a knob and then leaves the room. Some newer stoves have safety features to prevent this.

You need to teach everyone in the house that if they smell gas, they should
- NOT turn on any lights even if it is pitch dark
- not light matches or use cigarette lighters
- turn off the offending burner
- open windows and/or external doors
- then leave the room until it is vented.

If they can't locate the source of the gas leak easily then leave the house and call the emergency number of the gas supplier (if it's piped to the house).
posted by emilyw at 10:34 AM on July 25, 2014

CO sensor height doesn't really matter...I placed mine at about 4ft high on the bedroom b/c that was a convenient location just below the light switch. Anywhere between 2-6ft makes sense, but it'll work well enough on the ceiling too.

CO gas is almost the same weight as normal air, close enough to not matter, so all the drafts and air currents and heating in the house will mix it up pretty well. BUT if the boiler/etc is in the basement, then the basement will have a higher concentration than the next floor up, and so on.

My not-paranoid-but-still-cautious advice is to to put a CO detector just outside the room with the boiler, then if the bedrooms are on the same floor I'd put one in each of them too, and I'd put one on the main floor if the boiler is in the basement.
posted by jpeacock at 12:09 PM on July 25, 2014

The reason why gas leaks can cause carbon monoxide poisoning some places is because the gas is coal gas. It's made by baking coal in a sealed oven and capturing the gasses that are released.

Coal gas contains a lot of carbon monoxide; it's unavoidable. A gas leak of coal gas can kill you stone dead.

Gas was a major innovation in city utilities in the latter half of the 19th century, used for lighting, heating, and cooking, and that was always coal gas, in Europe and the US. But the development of more modern drilling technologies caused nearly everyone to switch to natural gas.

Natural gas is a mix of methane (primarily), and also ethane, propane, and butane. None of them are particularly poisonous, though all of them are explosive if the concentrations are too great. In terms of directly killing you (ignoring the explosion hazard) the only threat is if the concentration becomes so great as to reduce the oxygen available to you. Nitrogen in sufficient quantities can do the same thing. (I should point out that hydrocarbons are anesthetics, but the concentration required for that is extremely high.)

But long before natural gas reached those kinds of concentrations, it almost certainly would explode. (Not much of a consolation, I know.) The explosion risk is the only important one when it comes to natural gas, but it is real. And that's why the gas company adds trace amounts of an odorant to natural gas. The substance they use is one that we are acutely sensitive to and can smell in extremely small quantities, but which rarely occurs in pure form naturally, and we can smell natural gas with that odorant long before the gas concentration reaches an explosion hazard.

Any properly-designed stove or furnace which burns natural gas will not produce carbon monoxide. CO is produced if there isn't sufficient oxygen, and properly designed stoves and furnaces have their burners out in the air, with plentiful air flow. Any flame that is producing carbon monoxide will also produce soot. If you aren't finding soot on the bottom of your pans, you don't need to worry.
posted by Chocolate Pickle at 1:10 PM on July 25, 2014 [2 favorites]

Another point: Stoves, ovens, and furnaces are designed to mix air with the gas before it burns. Proof that it's working properly is that the flame is blue; that means there's enough oxygen for complete combustion.

If it isn't working correctly, then the flame will be bright yellow, like a candle. Even in that case, however, it probably isn't producing any carbon monoxide.
posted by Chocolate Pickle at 4:46 PM on July 25, 2014

- turn off the offending burner

On my stove, going from 'on' to 'off' goes right through 'light'. I've experimented with it and found that if I flip the handle fast, the sparks don't fire. Usually.

The electrical plug for the stove is accessible - unplugging that would prevent the sparks from happening, but the act of unplugging it might spark.

I'm not sure what I'd do if I came home one day and found the stove on but not lit and the house smelling of gas.
posted by Hatashran at 5:13 PM on July 25, 2014

To answer Hatashran, you go outside and turn off the gas main, then you and your neighbors all evacuate to the next block while you call the fire department.

If you can't locate the gas main or know how to shut it off, then skip straight to evacuation and calling the fire department.

Let the professionals handle it.
posted by jpeacock at 2:27 PM on July 28, 2014 [1 favorite]

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