Hi, I have a ~1969 Williamson furnace that came with the
house we bought 3 years ago. Now my wife asked me to check
the humidifier filter, because it says that you ought to
change it and clean the whole thing at the end of every
season. When I opened it today, it looked like it had never
been changed for the last 30 years, all corroded and crumbly
inside. So, now the question is, what to do?

(1) leave it alone, it will kinda work until the furnace
needs to be replaced anyway

(2) scrape some original parts off the web and clean it out
as good as possible

(3) replace the entire humidifier

(4) replace the entire furnace

I don't really want to do (1) because this thing is probably
full of legionellae or other airborne germs and stuff, which
is why I am considering (3). But will I get a humidifier that
even fits this whole setup?

The humidifier is a simple box at the side of the main inflow
airduct with a second duct forked from the main outflow. This
outflow-connected duct blows air through the humidifier filter
back into the inflow leg. The filter is constantly dripped
with water.

So, will I find the same kind of system to just drop in or
will it take major rework of the ducts and pipes?

If major work is needed, wouldn't it be better to change the
entire furnace+A/C system? (Yes the A/C element is part of
the system.) How much of the existing A/C stuff could be built
into a new system? I know that the A/C part had been redone
more recently so I want to avoid redoing it.

thanks for your advice,
-Gunther