Carbon monoxide issues and negative pressure

[sheneron]

Well, for the first time in a few years of lightly using my wood stove, my CO alarm (thankfully) went off last night while we were all sleeping and woke us up. Called 911, FD came out and confirmed CO and vented the whole house. The wood stove is the only combustion appliance I have in my house so it had to be that.

I suspect what happened is: As I went to sleep, the fire was dying and getting weaker. At some point the draft reversed (it seems I have some negative pressure in my house) and this caused the burning wood charcoals that remained in the stove to just pool CO inside the house.

One possible mistake I made was that I had the flue on the most closed setting (I just left it at that setting once I got up to temp originally) rather than the most open setting. Perhaps whenever I decide to let a fire burn out I should put it on the most open setting? But I don't think I have had an issue with this in the past.

I also wonder if using a bathroom fan while take a shower, as the fire went out, perhaps caused the draft to reverse in the stove.

I will have a professional company come take a look at everything and see what they say, but any thoughts on the above?

 

[spuldup]

Glad you had the CO detector! Yes flue open and inducer set to run through the last of the coaling phase. An outside air kit, if avaliable, will be best.

On cold nights (it was 14F here last) the downdraft is harder to overcome. Couple that with some funky wind direction and yes downdraft is possible on a dying/weak fire.

 

[Grinnell]

We heat with wood and i have 2 CO detectors and 5 combos around the cabin. Paranoid but alive.

 

[begreen]

Kudos for haveing a CO detector.

One possible mistake I made was that I had the flue on the most closed setting

Does this mean the air control on the stove or is there a key damper in the stove pipe?
Tell us all you can about the installation. Describe the flue system in detail. How many floor levels in the house and what floor is the stove on?

 

[Prometeo]

if you can also install an OAK,
in case of draft reversal, the monoxide will go almost exclusively outside, through the OAK

 

[sheneron]

Kudos for haveing a CO detector.

Does this mean the air control on the stove or is there a key damper in the stove pipe?
Tell us all you can about the installation. Describe the flue system in detail. How many floor levels in the house and what floor is the stove on?

The air control on the stove. I had it in the most closed position when I went to bed, so it would have been in that position as the fire died.

Below are pictures of the flue, which goes from the first floor (10ft ceiling), to the second floor (unfinished attic), to the chimney on the roof. The whole thing was installed by the original builder of the house. During my first chimney sweep, I was informed that the pipe on the first floor was incorrect material for a wood stove and needed to be replaced. I replaced it myself with DVL double wall stove pipe, which is what is shown in the picture. I used the same configuration/layout that was there originally (e.g., two 45 degree pieces).

 

[begreen]

The install looks straightforward. One thing to check is the cap. If there is a screen on it, that should be examined for buildup that might be weakinging the draft.

The bath fan, a radon fan, a competing appliance like a gas or oil furnace, could all changed the balance. With the next fire, open up the patio door 1/2" and see if that affects the fire. If so, it looks like it would be fairly easy to add an OAK to this setup.

 

[sheneron]

The install looks straightforward. One thing to check is the cap. If there is a screen on it, that should be examined for buildup that might be weakinging the draft.

The bath fan, a radon fan, a competing appliance like a gas or oil furnace, could all changed the balance. With the next fire, open up the patio door 1/2" and see if that affects the fire. If so, it looks like it would be fairly easy to add an OAK to this setup.

The cap should be ok because the sweep inspected the chimney a month or two ago and I have only burned a few times since then.

Open the patio door to see if it makes the fire more intense or what? Also, how exactly does an OAK help with the carbon monoxide situation. Is it just that it keeps a draft going up the chimney or is it that it allows a lower path for the CO to escape in case there is a back draft?

 

[NHWS]

Open the patio door to see if it makes the fire more intense or what? Also, how exactly does an OAK help with the carbon monoxide situation. Is it just that it keeps a draft going up the chimney or is it that it allows a lower path for the CO to escape in case there is a back draft?

Low indoor air pressure could reduce draft, or possibly cause a backdraft. Either an OAK or an open door/window would help support the indoor air pressure. Opening a door/window is a useful diagnostic test.

If opening a door/window helps, think about @begreen's suggestions. Also consider fuel-based hot water heaters (if you have one), dryers, cooking vents, and the air movement around the outside of the house.

If there's a backdraft even with an OAK or open door/window, a slightly open/door window would provide some escape route for the CO but It isn't likely to help much. The escape path is small compared to the room volume.

You don't want combustion products escaping via an OAK. OAKs are not designed to handle the temperature.

 

[Megunticook]

This has happened to me a few times in the past. CO alarm didn't activate but I smelled stove exhaust in the room upon waking.

Some ideas:

If your stove has a griddle top make sure the gasket is sealing well.

If the chimney has a screen at the cap make sure it's clean. I had issues with fly ash occasionally and eventually removed it.

If you have a catalyst make sure it's not obstructed with ash. I check mine periodically.

OAK is a good idea, I installed one from the get go. Removes indoor air pressure from the equation.

I only close my stove's air inlet down fully if I'm close to overfiring. At night I leave it slightly open. This totally depends on your stove and overall setup of course.