Baptistry n. : In early times, a separate building, usually polygonal, used for baptismal services. Small churches were often changed into baptisteries when larger churches were built near.

Baptistry n. : A part of a church containing a font and used for baptismal services.

Example:
Inexpensive way to heat water in 100 gallon portable Baptistry?

Taxonomy
baptistery, baptisteries, Lateran Baptistery, baptism, baptistery doors, Baptistry of Parma, church, the church, mosaics, free encyclopedia, catechumens, Constantine, Christian, immersion, rule, tomb, Pisa, baptistries.

Defination from the web:
baptistry (Latin baptisterium, from Greek βαπτίζειν) is the separate centrally-planned structure surrounding the baptismal font. ... and sometimes architectural splendor of the baptistry reflect the importance of baptism to Christians. ...