We live in 2 story home constructed in 1996. It has a gas furnace and a
gas water heater. The water heater was replaced in September 2004, and was
professionally installed and ANSI Z21.10.1a compliant. These are the only
gas-fueled items in the home. They are located next to each other in the
basement. When we had the home inspected prior to closing in 1996, all
installs and vents were up to code.

We have a Nighthawk digital readout CO detector in the basement, about 14
feet from the appliances. On August 4, I noticed the digital readout said
10 (ppm) and showed a stored high of 21. On August 1, the reading was 0
when I did the monthly test. It has been very hot here and we have been
running A/C constantly for about 3 weeks with all house windows closed. We
opened all windows, ran the blower fan without A/C, and readings returned
to 0 within an hour. Closed up the house, turned A/C on, reading was back
to 11 by the next morning. We bought a second Nighthawk and have duplicate
readings. We have never seen this in the past, the Nighthawk has always
read 0 and a stored high of 0. We actually test it and our smoke detectors
monthly.

Called our HVAC contractor, and he came out yesterday. The furnace does not
have a full-time pilot, he said it uses a glow igniter (?) and the furnace
checked out fine, and we change the filter monthly. He felt leaky ducts
around the HVAC unit were causing enough turbulence to prevent the water
heater fumes from venting properly. There *was* a lot of air blowing around
the ducts around the HVAC unit. He sealed all around the furnace, and a lit
match flame appeared to draw well to the water heater vent when he was
finished. This vent is also warm to the touch where it goes through the
ceiling; he said that indicated that there probably wasn't blockage in the
vent. So, we closed up the house, restarted the A/C, and at bedtime, the
readings were still 0. This morning, upon awakening, the reading was up to
16. Opened windows, ran blower fan, readings went to 0 in 45 minutes.

We have an appointment for next week for a plumber to bring a CO detection
device to pinpoint the source. In the meantime, we have the windows open
and 0 readings.

Does anyone have any ideas or gas water heater knowledge of what might
cause this sudden onset of detectable CO in the house?

Thank you!

On 6 Aug 2005 15:51:09 GMT, someone wrote:

... So, we closed up the house, restarted the A/C, and at bedtime, the
readings were still 0. This morning, upon awakening, the reading was up to
16. Opened windows, ran blower fan, readings went to 0 in 45 minutes.

Hmm, "closed up the house" and ran the A/C - - - my bet is that there
is insufficient make-up air available to run the gas burners (they
need fresh air for combustion that then goes up the flue pipe) when
the house is closed up and the A/C is on. You may be back drafting
with a suction from the A/C.

Traditional solution: open a basement window. Though nowadays peeps
want someting more sophisticated. But you could try it for a couple
of days to see if it helps?.



Reply to NG only - this e.mail address goes to a kill file.

(v) wrote:

On 6 Aug 2005 15:51:09 GMT, someone wrote:

... So, we closed up the house, restarted the A/C, and at bedtime, the
readings were still 0. This morning, upon awakening, the reading was
up to 16. Opened windows, ran blower fan, readings went to 0 in 45
minutes.

Hmm, "closed up the house" and ran the A/C - - - my bet is that there
is insufficient make-up air available to run the gas burners (they
need fresh air for combustion that then goes up the flue pipe) when
the house is closed up and the A/C is on. You may be back drafting
with a suction from the A/C.

Traditional solution: open a basement window. Though nowadays peeps
want someting more sophisticated. But you could try it for a couple
of days to see if it helps?.

Thanks for your reply. I appreciate your knowledge and your willingness to
help that I've seen for years on this NG. And in this case, a simple
solution would suit me best!

The basement window is glass blocks with a small insert that can be opened
for ventilation, located on the wall farthest away from the HVAC. We did
open this. We had shut off the A/C and blower fan, opened all upstairs
windows, AND the little basement window, and still got recordable levels of
CO in the basement after a few hours. We aired it out again by running the
blower fan, and later, because it got too hot, closed the windows and
turned on the A/C. CO level stayed at 0 this time. This was the day after
my original post. The plumber was here this morning with a CO detecting
instrument, and could find no evidence of a CO leak anywhere, and no idea
what had happened. They left an air monitor recorder, and will pick it up
in two days. So, for now, the situation is as it should be, and even with
all the windows closed, there is no measureable CO being produced now, nor
has there been for two days now. We're still baffled by this situation,
and don't understand why it would spontaneously appear and disappear...

On 9 Aug 2005 16:58:47 GMT, Amateur wrote:

(v) wrote:

On 6 Aug 2005 15:51:09 GMT, someone wrote:

... So, we closed up the house, restarted the A/C, and at bedtime, the
readings were still 0. This morning, upon awakening, the reading was
up to 16. Opened windows, ran blower fan, readings went to 0 in 45
minutes.

Hmm, "closed up the house" and ran the A/C - - - my bet is that there
is insufficient make-up air available to run the gas burners (they
need fresh air for combustion that then goes up the flue pipe) when
the house is closed up and the A/C is on. You may be back drafting
with a suction from the A/C.

Traditional solution: open a basement window. Though nowadays peeps
want someting more sophisticated. But you could try it for a couple
of days to see if it helps?.

Thanks for your reply. I appreciate your knowledge and your willingness to
help that I've seen for years on this NG. And in this case, a simple
solution would suit me best!

The basement window is glass blocks with a small insert that can be opened
for ventilation, located on the wall farthest away from the HVAC. We did
open this. We had shut off the A/C and blower fan, opened all upstairs
windows, AND the little basement window, and still got recordable levels of
CO in the basement after a few hours. We aired it out again by running the
blower fan, and later, because it got too hot, closed the windows and
turned on the A/C. CO level stayed at 0 this time. This was the day after
my original post. The plumber was here this morning with a CO detecting
instrument, and could find no evidence of a CO leak anywhere, and no idea
what had happened. They left an air monitor recorder, and will pick it up
in two days. So, for now, the situation is as it should be, and even with
all the windows closed, there is no measureable CO being produced now, nor
has there been for two days now. We're still baffled by this situation,
and don't understand why it would spontaneously appear and disappear...


Polution coming in from the outside perhaps? Maybe when you opened up
the house was a time when commuting was over, or some sort of thermal
inversion cleared up letting the overall polution level drop.

Chris Hill wrote:

On 9 Aug 2005 16:58:47 GMT, Amateur wrote:
We're still baffled by this situation, and
don't understand why it would spontaneously appear and disappear...


Polution coming in from the outside perhaps? Maybe when you opened up
the house was a time when commuting was over, or some sort of thermal
inversion cleared up letting the overall polution level drop.


We just don't know. We're in a small housing subdivision surrounded by
farmland; closest highway is about 6 miles away. For a few days, the level
of CO would rise when there was no air movement in the basement. 48 hours
of air monitoring revealed nothing out of the ordinary; the situation
disappeared as mysteriously as it started. We've been in this house for
nearly 9 years, and have never seen this before. HVAC and plumbing
professionals could not provide probable causes.