Martik wrote:

"Robert Gammon" wrote in message
m...
Todd H. wrote:
"Martik" writes:


Are you referring to the chimney for the furnace? Why would anyone put
something in there. Sounds like a good way to murder someone! Luckily we
have 2 CO detectors.

Birds have a nasty habbit of not informing homeowners of their nesting
plans. If only the birds would follow the permit process, by god,
lives would be saved.


Given that the top of the stack is a protected entrance, it will be
DIFFICULT, but not impossible for small birds to get in there. The gap
to my fireplace is a bit larger than my furnace flue, and small birds do
find their way to the fireplace from time to time. In 28 years, never
such an incident in either gas water heater or gas furnace.

A maintenance worker sticking a rag down the flue and forgetting to take
it out seems to be a more likely scenario. such an action is more
likely to occur at the bottom of the stack, at the furnace, rather than on
top of the roof.

Is there a sensor to detect lack of free flow thru the chimney that would
shut off the gas?

There are draft sensors that could detect blockage, but they are not
generally used. The much more common CO detector would detect such
conditions if properly installed and maintained.

Unfortunately some people install CO detectors right next to the furnace
and then eventually unplug them after too many false alarms due to
momentary back drafts from wind gusts. They need to be installed a
sufficient distance away so those non-threat conditions do not give
false alarms.

Pete C.