Carbon monoxide

So let me pop open this can of worms...

We just got our new insert. 1st night, great fire - left hvac fan on all night to distribute nice heat through house. 2nd night - wonderful fire again, choked it down for slow burn, went to bed but didn’t leave fan on. 3am - carbon monoxide alarm in basement near stove wakes us up. Outside we go, 911, fire department shows up and is excited that it’s really CO and not just another low battery. The house is aired out - and thinking it could have been the stove we clean out the smoldering ashes and go to bed. No smoke smell, but never had an alarm before the stove.

Our only CO monitors were our nest protect smoke alarms and through all this I found out they only alarm after 1 hour of 70ppm. I figured out how to download historical data and not only did we have elevated levels (40s) the night before, we’ve had them on nights with fire in the conventional fireplace before the stove was installed.

So last night I investigated with a new low range CO tester. Got a nice fire going - drafting well. Turned on all the exhaust fans in the house, furnace, and water heater. Everything drafted fine - no leaky vents and 0 CO at any of the possible sources.

Then I choked the fire down to low, same as the other nights, and waited. My patience was rewarded around 2 am when my CO detector shot up to 70, coming straight out of the stove air intake. It was backdrafting with smoldering coals still inside.

My biggest problem is probably an outside masonry chimney. Full liner, but not insulated. I’ll be looking to insulate it soon but for now I’m going to burn the fire out at the end of the evening rather than set it up for an overnight slow burn and crack a window.

Anyone else had hot backdrafts and/or CO issues? Any other thoughts on how to manage this?

Thanks HomeinPA, I was leaving The air intake all the way closed. Had good secondaries when I went to bed, but maybe it’s just too much.

Thanks for the concern bholler, I certainly don’t want to breathe any more CO. I do have 4 CO detectors in the house, including a new low level one that alerts at 30 near the stove. I know the issue is a backdraft at the very end of the burn, so looking for ways to address that. I’m just not sure if the best options are outside air, flue insulation, or maybe just not choking it down so far.

weatherguy said:

What floor is the stove? Basement or first floor?

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The stove is in the basement

Ctwoodtick said:

There is an issue with your setup. Once my wood is engaged, I set air control to lowest setting and do not have my co detectors going off. Stove should always be pulling air in, not the other way around. Good they you posted your question on here. While you gave a humorous way of posting, please don’t allow yourself to be lax about this issue. CO has no smell and can kill you. Have set up looked at before using again. Simply using a different setting is not your fix. Very bad advice from the person who said that above.

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Believe me, after a late night in the yard letting the fire department air the house out, I am taking it very seriously. The set up was looked at immediately after the incident and all connections were good. Curious though, if you have negative pressure in your house, won't the stove eventually backdraft just like a regular fireplace chimney does the day after a fire? There is no backflow preventer to keep it from doing so, and eventually the system would cool to the point that negative pressure in the house would pull air back down. The problem seems to be that this is happening while it is still smoldering.

Does anyone here use a low level CO detector? I was upset to find out through all of this that a conventional CO detector in the US won't alarm until levels stay at 70. OSHA requires exposure to stay below 30, and WHO recommends below 9 for residential. You wouldn't ever know if you had a low level issue with a standard detector.

jetsam said:

Is the pipe taller than the ridgeline of the roof? How far apart are they?

The insulation is a good idea and will help draft, but it still shouldn't be reversing as it cools off.

Is an outside air kit possible with your insert?

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The pipe is taller than the roof ridgeline, about 4 feet above.

I think negative pressure is my biggest issue so outside air is probably going to be the best solution. I did burn a fire with a window in the basement cracked last night and got 0 on my low level meter by the stove all night. This insert doesn't allow for a direct OAK connection, but I can set up an outdoor air vent near the stove. I also do not have a combustion air supply for my furnace, so all ventilation in the house depends on air leakage.

Rearscreen said:

Any chance your furnace is kicking at that time in thus changing basement air pressure?

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Yes - I do think that is a factor, and it is about 20 feet away in a connected room in the basement and depends on inside air for combustion. I also have a radon mitigation system that sucks air from under the slab. I'm not sure if this is contributing to the negative pressure in the house, but certainly doesn't help. All things point more and more to needing more makeup air.

jatoxico said:

This a common problem with basement installs. Look up Stack Effect, furnaces and other sources of negative pressure like fans etc only worsen the problem. You may be able to improve the situation by air sealing especially in the attic, so ex. a leaky set of attic stairs would be an issue.

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The attic steps are sealed with a foam insulating cover. But, I took a look up there anyway and it turns out there is a large hole right beside where the furnace flue comes through the ceiling, Looks like it was sealed but got broken at some point. I can feel a nice warm breeze blowing all my precious heated air right into the attic. Seems like this could be a significant contributor to my issue (and my gas bill). Going to get this sealed up today. Thanks for the tip!!

vwmike said:

What kind of insert? Is there a clean out you can use as outside air supply behind the insert?

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It’s a fireplace x (Lopi) flush wood plus. I don’t believe there is any way to hook it up directly to outside air.

The hole is fixed!

The previous owner's attempts at sealing the area around the gas furnace flue included a mish mosh of particleboard, drywall (most of which was broken), insulation, and even a piece of cardboard nailed in place . Now it is sealed with aluminum flashing and some high temperature sealant. I don't know if this fixes everything, but I will say the downstairs chimney has always had a very strong backdraft that I had to fight to start a fire, before and after the insert went in, and right now there is nothing.

Had a wonderful fire yesterday evening and peak CO level for the whole night was 0. The firebox is cooled off now and still no reverse draft so it looks like this thing is doing what it should. I can't remember ever having a fire downstairs before where it wasn't cold and stinky down there the next day. So nice to walk down to a warm room.

Thanks for everyone's concern and advice, and jatoxico thank you so much for the tip that saved the day!

I am very thankful for my CO alarms and hope I never have to hear them again.