I have 2 wholehouse humidifiers attached to the furnaces. The excess
water is drained out through a 1/2" tube. The tube outside the house is
about 2 feet long. No problems for 4 years.
Yesterday I noticed water in the basement. Upon investigation, found
about 1/4" water around water heater and furnace. My first thought was
that the water heater broke (6 years old). Then I saw water dripping
from under the drain pump attached to the furnace. Went outside and
found that the tube coming out of the house was filled with ice
crystals.
What probably happened is that the drain water backed up over several
days and overflowed out of the pump. For now I unplugged the pump,
turned off the humidifiers and cleaned up. (the carpet outside the util
room is wet, so need to do more drying :-()

Anyway, why did the drain water in the tube freeze now? 1st time in 4
years.
Also, how to avoid this? Someone suggested I keep the drain tube coming
out of the house very short (maybe 6 in). But in freezing cold the
dripping water could still freeze and lead to water backup. Any ideas?
Thanks.
Mark Sabatini