So many times I’ve read that wood burners don’t need to worry about CO because you would smell the smoke if the flue was clogged or if you had a reversal, and that would tip you off to the danger.  I have always thought that the most dangerous time is after the fire cools and all you have left is a bed of smokeless charcoal.  I got proof of this earlier in the week.

The other day, I went down to tend the stove first thing in the AM.  I knew ahead of time that I had a huge bed of coals because I could feel the heat as I opened the basement door.  I looked at the stovetop thermo and it was at 325º.  I opened the damper and peaked into the stove and there was about 6” of hot coals sitting on top of a couple days worth of ashes. The air intake was buried.  I used a poker to clear a channel next to the intake, but I wasn’t happy, so I decided I would deal with the hot coals and get some of the ashes out.

I grabbed the rake, knelt down in front of the stove and opened the doors.  It was a real hassle shuffling the coals from side to side, but in about five minutes I had half a bucket of ashes out of the stove and covered in a bucket.  Then I reached over to grab a couple of small splits and threw them on the coal bed.  They almost self-ignited when they hit, and when they did, a big cloud of smoke came pouring out of the top loading door.  I had forgotten to close the griddle top!

You can fill my stove with the griddle top open without losing the draft of the chimney, but having both the front doors and the top door open completely bypasses the flue, and the hot gases will just rise into the room itself. I quickly closed the top and then shut the front doors to let the stove fire up to temp.

My CO detector is in the bathroom directly at the top of the stairs.  Theory has been that any CO would rise with the hot air and enter the bathroom doorway.  The first thing I always do every morning is to check the detector before my morning pee for a possible trace level (mine won’t sound the alarm until 70 PPM has been in the air for a while, but it will detect and record levels as low as 10 PPM). It’s always said “0” at this point, but when I pressed the button this time, I got a reading of 20 PPM.

So the thing works, and I’ve got it in the right spot, so that’s good news.  The major eye opener here is that, until I added fresh wood, I never noticed or smelled anything coming from the stove.  If by some chance I got distracted and walked away with both the top and the front doors open, I would have surely gotten a lot higher reading than 20 PPM.  And if I had gone back to bed, and if I didn’t have a quality CO detector in the correct spot, I might not be writing this now.

So disregard anything anyone tells you or that you read about on the Internet.  Dangerous levels of CO gas are always forming at the end of a burn, and you won’t smell the fumes because the smoke is long gone.  Be safe.  Get a CO detector (or two) if you haven’t already done so.

I thought that with the new epa stoves that the firebox would only draw air from the room.  The coals are definitely consuming air.  With the convective process pulling all the gases up and out the chimney?  Some gases could escape out the door while you are raking the coals.  Or am I wrong?

A stove will vent to the best chimney around.  If that happens to be your house because it drafts better than your actual chimney, the stove will run that way.  This usually isn’t an issue when the stove is going, but reloading or first starting up this can be a problem.

Matt

Battenkiller - 09 February 2010 01:34 AM

So many times I’ve read that wood burners don’t need to worry about CO because you would smell the smoke if the flue was clogged or if you had a reversal, and that would tip you off to the danger.  I have always thought that the most dangerous time is after the fire cools and all you have left is a bed of smokeless charcoal.  I got proof of this earlier in the week.

The other day, I went down to tend the stove first thing in the AM.  I knew ahead of time that I had a huge bed of coals because I could feel the heat as I opened the basement door.  I looked at the stovetop thermo and it was at 325º.  I opened the damper and peaked into the stove and there was about 6” of hot coals sitting on top of a couple days worth of ashes. The air intake was buried.  I used a poker to clear a channel next to the intake, but I wasn’t happy, so I decided I would deal with the hot coals and get some of the ashes out.

I grabbed the rake, knelt down in front of the stove and opened the doors.  It was a real hassle shuffling the coals from side to side, but in about five minutes I had half a bucket of ashes out of the stove and covered in a bucket.  Then I reached over to grab a couple of small splits and threw them on the coal bed.  They almost self-ignited when they hit, and when they did, a big cloud of smoke came pouring out of the top loading door.  I had forgotten to close the griddle top!

You can fill my stove with the griddle top open without losing the draft of the chimney, but having both the front doors and the top door open completely bypasses the flue, and the hot gases will just rise into the room itself. I quickly closed the top and then shut the front doors to let the stove fire up to temp.

My CO detector is in the bathroom directly at the top of the stairs.  Theory has been that any CO would rise with the hot air and enter the bathroom doorway.  The first thing I always do every morning is to check the detector before my morning pee for a possible trace level (mine won’t sound the alarm until 70 PPM has been in the air for a while, but it will detect and record levels as low as 10 PPM). It’s always said “0” at this point, but when I pressed the button this time, I got a reading of 20 PPM.

So the thing works, and I’ve got it in the right spot, so that’s good news.  The major eye opener here is that, until I added fresh wood, I never noticed or smelled anything coming from the stove.  If by some chance I got distracted and walked away with both the top and the front doors open, I would have surely gotten a lot higher reading than 20 PPM.  And if I had gone back to bed, and if I didn’t have a quality CO detector in the correct spot, I might not be writing this now.

So disregard anything anyone tells you or that you read about on the Internet.  Dangerous levels of CO gas are always forming at the end of a burn, and you won’t smell the fumes because the smoke is long gone.  Be safe.  Get a CO detector (or two) if you haven’t already done so.

20 ppm CO is nowhere near dangerous.  In fact, that is a level that you shouldn’t even notice.  The Immediately Dangerous to Life and Health Level for CO is 1200 ppm, that means that @ 1200 ppm you are in danger of dropping on the spot.  OSHA sets their exposure level @ 50 ppm (another agency says 35 and is a more safe level).  The thing to remember is that that level is for an 8 hour time weighted average.  That means that a short term exposure (5-20 mins) @ 35-200 ppm are not a large cause for concern.  It can cause headaches etc. but will not cause lasting effects.

It is also helpful to understand COs effect on the body.  Co is NOT Plutonium, or Asbestos.  That is to say that CO presents us with an acute hazard.  The effects of limited exposure to CO are short term and WILL go away given time and sufficient oxygen.  It does not cause cancer.  COs hazards present from the fact that it is a chemical asphyxiant.  That means that when inhaled, the hemoglobin in your blood is more likely to pick up the CO than it is to pick up the O2 in the air.  Too much CO will cause your hemoglobin to be saturated with CO and no room to carry O2 to the places it needs to.  This is why removing the victim to fresh air is sufficient in most cases to eliminate the effects of CO.

I can almost guarantee that you are exposed to a higher level of CO in your car in the morning than when working on your stove.

All that being said, CO is colorless and odorless.  You will never know what got you without a detector.  If you burn LP or Natural gas in your home you should have one.  The same for a woodstove.