Lately I've been noticing a specific smell in the house. It's
something I've smelled before in other houses I've visited or lived in
with gas appliances (heat or otherwise). I'm going to guess that it is
a "burned gas smell". It smells faintly like unburned gas and
something else, like 'heat' i guess, even sometimes a little bit like
kitty litter. I know that's a bit silly, but I can't think of anything
else that smells similar, and on top of that my nose doesn't work so
well anyways. In fact, the Missus says she can't smell what I'm
talkinga bout at all.

We have a 2-story house w/ no basement. There is a gas boiler and a
gas water heater on the first floor under the stairwell, behind some
vented doors. They both vent into the same chimney via a Y-pipe. It
is passive- i.e. no fans, turbines etc to blow the exhaust out- just
heat and gravity. The space that these are in is definately where the
smell is coming from, and AFAICT it's the boiler that's doing it. It's
most intense in that end of the house when the boiler has been running
a bit. When the boiler is not running, I can sniff around it and still
smell it. I fired them both up individually and held a cig lighter
flame near the cold air intakes of the exhaust tubes for both devices.
The water heater definately draws the flame inward (indicating a strong
upcurrent). The boiler's exhaust is kind of hard to tell because of
the way it is shaped. A stick of incense, maybe....

I have a brand new Nighthawk branded CO detector that I got from the
Borg. It is mounted in the stairwell above the same stairs that the
boiler and water heater are underneath. Finding the right place for it
is a bit of a challenge- away from doors (drafts falsely give low
readings), away from the appliances (which may falsely give high
readings), etc. You can look at my house as a cube, and it is mounted
about in the dead center of the whole thing. It always reads 0ppm.
According to the manual, it won't readily display anything under 30ppm,
but it has a sequence that you can use to display the 'high reading'
which it will show down to 19ppm. Still, it always reads 0ppm. I
removed it from the stairwell once and set it on a table in a
relatively close proximity of the boiler and water heater, expecting to
get some (albeit false) reading out of it. Still 0ppm.

I don't really know how 'normal' it is to smell "this smell". Is
the

1) A way to test a CO detector to ensure it isn't a factory "dud"?
2) A way to otherwise test for CO levels in the house and verify
safety?
3) Someone I can call to look at the appliances and ensure they're
functioning properly? Is this a job for the standard "Heating/AC" guys
in the yellow book, or someone else? Do they usually rove around them
with some sort of "sniffer"?

Thanks for any and all suggestions. I understand that "uhh... i smell
this smell" doesn't tell you much.

-phaeton