aldol condensation can be accomplished:
1) Thermally (heat)
2) Acid catalyst
3) Base catalyst
Source:
http://www.organic-chemistry.org/namedreactions/aldol-condensation.shtm
"In some cases, the adducts obtained from the Aldol Addition can easily be converted (in situ) to α,β-unsaturated carbonyl compounds, either thermally or under acidic or basic catalysis."
So I guess heat is not always required. My McMurry textbook discusses condensation using the acid/base catalyst, but does not mention heat; however, Kaplan says heat is required, but does not mention a catalyst.
Hope that helps