"Robert Gammon" wrote in message
m...
Martik wrote:
"Robert Gammon" wrote in message
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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.



I have a condensing furnace with both intake and exhaust horizontally
vented thru PVC and a draft inducer fan. Would this furnace have a safety
shutoff.


Nope, it RELIES on the fact the the exhaust vent AND the supply vent are
UNOBSTRUCTED. Both vents MUST be inspected on a REGULAR basis to ensure
that gas is free flowing thru BOTH of them.

I put my hand over the intake vent (outside) and the furnace shutdown within
2 secs.