"Lp1331 1p1331" wrote...
FWIW, the switch is not there to prevent anyone from sticking their
hands into the blower or getting shocked. It is there to insure that the
blower door is put on properly so that the blower does not cause a
negative pressure in the furnace room or closet and cause deadly fumes
to be sucked into the system. That is the most common cause of CO
poisoning with central heat, at least around here. Preventing injuries
from the blower itself or live electrical connnections is a fringe
beneft of the switch. If it was the main concern, they would have them
on air handlers and electric furnaces also, which they do not-- at least
on any I ever saw. Larry

Makes sense. Quite interesting. Not such a silly thing after all I guess.
Can you explain how this thing works a little more with the "negative
pressure" business? I guess what you're saying is that the air should be
drawn from the cold-air intake and not from the furnace room surrounding
area and this thing is built to ensure that? That seems a bit surprising
since it's not like vapor-lock sealed or anything of course, and I had
always assumed a certain amount of air would be sucked in from the
surroundings but you're saying no that absolutely should not happen. So
very interesting... But isn't it still a problem if there's CO in the
surrounding air of the furnace anyway? I mean, that's part of the house
too... How does CO escape from the natural gas and blower system anyway?