CO in house, a mystery....

[Wip]

my neighbor had her CO detector go off yesterday. We called fire dept. CO was over 200 all through the house. The fire dept spent a couple of hours airing the house out. She has a gas furnace and water heater, that's all. Aired out house. tore furnace (Janitrol standing pilot) apart to inspect all innards. Even pulled heat exchanger. It was perfect. inspected flue (short run with the water tank exhaust joining in). Got some rust but everything was clear. I did notice the water heater flue stuck into the main a couple of inches. I trimmed it down to be about 1/2 inch inserted. re-assembled and things run just fine, good draw on flue, flames nice and blue, no rolll out on either appliance. put 3 digital CO monitors in house and ran thew furnace and water heater overnight (no one in house). Monitors show "0" CO even when checked for "peak CO".

Do you suppose the partial blockage from the water heater vent was the culprit? I can't come up with anything else.....

[RegUS_PatOff]

What location (city) ?

Snow, bird, nest, blocking exhaust vent, ect..

Vent straight up through the roof ?

One / two family house/ apartment/ condo ?

Any neighbor/apartment/condo sharing Flue ?

Is there any Damper (mechanical or electrical) on any exhaust flue ?

Was she using her gas(?) Oven that day ?

Does she have any other gas appliances ? fireplace, etc ...

Any attached car garage or nearby driveway ?

 

 

 

 

 

[Wip]

Located in ohio. single family ranch house with attached garage. flue is clear, inspected it top to bottom. no other gas appliaces. No dampers.

I don't believe she was running her car in the garage but will have to check on that later today.

[denrayr]

what about the combustible air intake? is it clear and unrestricted?

[Wip]

no seperate intake. it is a stardard, "old school " furnace: standing pilot, 3 burner, nothing fancy at all. It's in a finished basement of a 45 yearold house.

[Cactus Bob]

gas dryer ? stove ? wall oven ?   was it real windy out that day ? 

[Wip]

just a furnace and water heater sharing the same vent (6 inch) .  No wind to speak of. Its windy today and all is well though.

[denrayr]

Wip wrote:

no seperate intake. it is a stardard, "old school " furnace: standing pilot, 3 burner, nothing fancy at all. It's in a finished basement of a 45 yearold house.

the mechanical room should have a flue or vent for fresh air to enter to replace the exhaust air that goes out the vent.

[RegUS_PatOff]

maybe not in a separate room, or if it is, may just have a "louvered vent" in the entrance Door

[RegUS_PatOff]

[user=5325]Wip[/user] wrote:

... I don't believe she was running her car in the garage but will have to check on that later today...

She may not remember (forgot, and left it running).

Check to see if keys are in the ignition.

Ignition ON.

Now out of gas.

Now dead battery.

 

 

[Wip]

I did check on the car, no, it had not been running. the furnace is in an open area with nothing blocking the air flow to it. No doors to close it off from the rest of the house.

So, to summarize: high CO reading 200+

Only gas appliances are furnace and water heater

good heat exchanger, burners, controls (standard furnace) no flame roll out

water heater is fine too.

No unusual weather.

flue is short and  clear, checked from both ends.

As I said the only thing I found was the point of entry of the water heater to the flue. the water heater's pipe extended maybe 1.5 inches into the flue pipe. I trimmed it off to be about .5 inch. It's been 10 years since anything was done to either (hot water tank is that old).

[denrayr]

there has to be a makeup air somewhere, otherwise the house will be under negative pressure and the exhaust wont go up the flue. If the makeup air gets partially blocked it can happen intermittently.

[RegUS_PatOff]

[user=5325]Wip[/user] wrote:

... 45 yearold house.

1964 .. house has all kinds of "makeup air" intakes ...  

unless the basement door is well sealed from the rest of the house ...

[denrayr]

[user=3641]RegUS_PatOff[/user] wrote:

[user=5325]Wip[/user] wrote:

... 45 yearold house.

1964 .. house has all kinds of "makeup air" intakes ...  

unless the basement door is well sealed from the rest of the house ...

i missed the age of the house, have the windows and doors been updated? I guess im stuck on the makeup air because he ruled out all other causes and they really make a big deal about it around here. the gas company will red tag a dryer if the laundry room doesnt have a vent to the rest of the house allowing makeup air in the laundry room.

[neurodoc]

It is possible that the bit of water heater flue extending into the furnace flue was enough to cause a backdraft. Since you've excluded a cracked heat exhanger, flue leaks, and a running automobile in the attached garage, the only explanation for the high CO level is a backdraft. This can be caused only by an inside

[neurodoc]

Sorry, my reply got cut off. I was saying that the only way for CO to build up inside a house is for outside air pressure to exceed inside air pressure, resulting in backdraft. You've ruled out a cracked exchanger or flue leaks or a running automobile in the attached garage. The water heater flue projecting into the furnace flue could certainly cause backdraft. All combustion flues have "draft diverters" that normally allow inside air to aid in flue discharge. With a pressure reversal they can allow combustion gasses to enter the inside of the house. The best way to assess for this condition of pressure reversal is with a manometer.

Nick

[Bobice]

Not to be a pain, but did anyone perform a "Combustion Efficiency Test" ?

[Dadmech]

Just a note... Most household CO meters are cumulative and don't show an "instant" reading. were readings taken by fire department CO meters?

Bob

Pittsburgh, PA