|The image below shows the top of a gas fired
water heater, the part to the right is the vent
for the water heater, it has openings to allow
air to be drawn into the vent pipe allowing
there to be a positive draft. if the vent is
clogged, by any number of things, like snow a
nest or other. the fumes from the burnt gas will
spill back into the house. some gas companies
require spill switches to be connected to the
draft hood, to shut the water heater off, if the
fumes start to come out of the vent hood, i
don't know why all gas companies don't require
this safety device, it saves lives. Anyway this
water heater does not have one so the water
heater is pouring fumes that contain carbon
monoxide into the home. How do I know this? see
the pipe to the left, covered with black foam
insulation? notice how the insulation is melted?
that's how I noticed. I make a point of checking
all gas fixtures for a positive vent whenever I
service anything in a persons home.
Snow buildup on the roof covered the top of the vent pipe preventing it from venting outside, so it vented inside, no one was harmed but the potential was there. Have spill switches installed on your gas water heater, even if tour gas company does not require them.