The Cottagers saw off Norwich 3-0 in their third-round replay in London.
"For sure it's the clean sheet," Hangeland told BT Sport. "We've conceded far too many goals and one of our main targets was to keep that clean sheet today so we've very pleased.
"We need to find the right balance between attack and defence. Lately we've been conceding too many goals so hopefully this is step in the right direction."