On Sat, 17 Feb 2007 01:28:23 -0500, "badgolferman"
wrote:

He shined a light into the the right side heating chamber and I could
see a hole and light through it in the seam at the end of it and plenty
of rust covering up the burner. The other two chambers were good.
Another guy told me a few years ago it was on the edge and wouldn't
last much longer.


If you can see a hole in the heat exchanger large enough for light to
shine through you should be having constant nausea, vomitting and
maybe even a death in the family from carbon monoxide poisoning by
now. If your sense of smell is normal you should be able to smell
burnt gases whenever your furnace fires up (1).

The same assessment of cracked tubes from three contractors and not
having at least one insisiting that you have it fixed immediately is
professional negligence. He likely has a professional obligation to
inform the gas company if you refuse to act on a potentially fatal
problem with your furnace. My argument is based on the fact that if a
civil engineer (a brother in law) is asked to sign off on a structure
that in his professional opinion is incorrectly designed and will
collapse and kill someone he has to refuse that commission and report
that to his professional body.

Skip the lawer part of it. Get that gas company to make that free
inspection. The gas company really does have a stake in your safety
and will never lie to you.

That said the heat exchanger is like a radiator that has spaces (aka
holes) in between the tubes so that the burnt gasses can pass through
them to the stack. Natural gas has a max temp of 2148°C which is why
the fan has to be on first to keep the tubes within operating
temperatures. If the thermocouple interlock senses overheating it
will shut down the burners. At that temperature plain cast iron is
the best material as any alloy or alloy coating will be burnt off.
Constantly heated cast iron looks rough and "rusty"

(1) Excerpts from Wikipedia:
http://en.wikipedia.org/wiki/Natural_gas
In any form, a minute amount of odorant such as t-butyl mercaptan,
with a rotting-cabbage-like smell, is added to the otherwise colorless
and odorless gas, so that leaks can be detected before a fire or
explosion occurs. Sometimes a related compound, thiophane is used,
with a rotten-egg smell. Adding odorant to natural gas began in the
United States after the 1937 New London School explosion. The buildup
of gas in the school went unnoticed, killing three hundred students
and faculty when it ignited. Odorants are considered non-toxic in the
extremely low concentrations occurring in natural gas delivered to the
end user..

http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning
Carbon monoxide poisoning occurs after the inhalation of carbon
monoxide gas. Carbon monoxide (CO) is a product of combustion of
organic matter under conditions of restricted oxygen supply, which
prevents complete oxidation to carbon dioxide. Carbon monoxide is
colorless, odorless, tasteless, and non-irritating, making it
difficult for people to detect.

Carbon monoxide is a significantly toxic gas with poisoning being the
most common type of fatal poisoning in many countries. Symptoms of
mild poisoning include headaches and flu-like effects, larger
exposures can lead to significant toxicity on the central nervous
system and the heart. Following poisoning often long term sequelae
occurs. Carbon monoxide can also have severe effects on the fetus of
pregnant woman.

The mechanisms by which carbon monoxide produces toxic effects are not
yet fully understood but hemoglobin, myoglobin, and mitochondrial
cytochrome oxidase are thought to be compromised. Treatment largely
consists of administering 100% oxygen or hyperbaric oxygen therapy,
although the optimum treatment remains controversial. Domestic carbon
monoxide poisoning can be prevented by the use of household carbon
monoxide detectors.