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?




Not that I am aware of. It would require putting an electrically
operated damper in place, closing it, then venting a quantity of vapor
and attempt to detect back pressure. If only atmospheric pressure in 5
seconds after release, then open damper and allow furnace to run. Need
a largish supply of compressed air or an air compressor and a bottle to
store the gas.

This system would add at least $500 to the cost of the furnace.