Has anyone ever dealt with a carbon monoxide leak in their home? Two days ago while BF and I were 2 hours away from home up a mountain scouting for spring bear, we get a frantic call from his sister (our landlord) saying that the CO meter in our suite is going off. Nothing we could do about it at the time so they dealt with it (had a family friend in the fire department pop by and "check" the house. Nothing was "found" so they opened windows and doors to air it out.) They didn't tell us exactly what the reading was. We get home and meter is reading 0ppm so we shut up doors/windows again and chat about what might be the issue. Gas appliances in the house re 1 gas fireplace downstairs, 1 gas hot water tank and 1 gas furnace both downstairs as well as a gas range stove upstairs. We had the gas fireplace on quite low so they shut that off and we hoped it was that. Next morning (yesterday) BF is at work, I go out for a few hours, come home and landlord/sister has dropped off a new CO meter for us just in case as we wondered if the other one was defective. So I plugged it in and within 5 minutes it was spouting off a reading of 100+ and climbed to 129ppm. ("acceptable" indoor range is 9ppm, 25ppm should be concerning, 50ppm is when the alarm starts to sound, 100ppm is enough to call 9-1-1.) Race upstairs, tell the landlord, talk to her husband and he hums and haws about calling the fire department and I INSIST he call the fire department. He does, and they arrive 5 minutes later. I've at this time opened all windows and doors again. They come through with their reader and basically just confirm that there are on and off high levels everywhere. Inspect lots of stuff, talk with homeowners, basic info is (and please excuse me as my knowledge and info on all of this isn't 100%): Could be venting from furnace? The venting for that is currently out the side of the house instead of the stack that goes out the roof for a few reasons, big one being lots of the work done on house before they owned it wasn't done to code. BF is a plumber and gas fitter and installed the furnace and hot water tank within the last 6 months and has been slowly working at fixing up stuff. The roof to this house will be getting re done soon due to some leaking and the landlords had a friend of the family check it out and I guess the stack where this all is supposed to vent from was leaking into the attic a bit so he put something on top of it partially to stop water getting in which has compromised the venting and is maybe causing the carbon monoxide to be pushed back down into the house? Could be due to a bit of both? BF and I tested the hot water tank's venting yesterday twice and it looks to be venting decently but maybe not 100%? So basically, the fire department said "leave windows and doors open, maybe have gas company out to shut off gas to house and test (which we haven't yet done as BF wants to do some stuff first) and get that venting fixed. They also climbed up on roof and removed the "cover" that was put on the stack. So we had all doors upstairs and downstairs open as well as fans downstairs running to air the place out and reading went back down to 0ppm. BF and I left for evening to have Easter dinner with his folks, get home around 8:00pm and our meter is reading 35ppm and climbing into the 40s. Our doors and windows were still open, landlord upstairs had shut hers apparently and she said she had run the furnace a bit because her house was cold (don't get me started on that...) So we air out house...again, and try and test to see where it's coming from. Can't figure it out. Stay up until 10 or so and meter goes down a bit. Go to bed, wake up at 11:45pm to the alarm going off, 55ppm. Air house out again, even though windows were still open. Get the alarm to stop finally and leave fans running and windows open all night. Wake up this morning at 4am and it's back down to zero. I brought my dog with my to work today as I didn't want to leave her at home to suffocate, no idea yet how readings are as no one is home until 2:30 earliest. BF's plan tonight is we are going to first, air out house, fun furnace for an hour and see if it spikes levels. Then air out and run hot water tank to see if it spikes levels. Then hopefully figure out whats causing it. He's going to pull apart furnace to see if there is a broken part (don't remember the name for the life of me). We are also going to inspect chimney/venting stacks to see if a birds nest or SOMETHING is blocking any of them. But basically right now we are extremely confused, overwhelmed, and at a loss as to WHAT is causing this all of a sudden. Any input, suggestions, advice?! We are talking CO levels that could kill us if we sleep and they get too high. It's very frustrating because it seems like there isn't one professional who we can go to who will say "THIS is your problem, for sure." I'm trying to convince BF and landlord to have Fortis (gas company) out today and have them test as their readers are more accurate than the fire departments, and maybe they can pinpoint where it's coming from exactly but they cost to have out and they want to try testing the furnace and hot water tank ourselves, first. Help?