NuTone C909 Tri-Volt Transformer for Door Chime 8-volt, 20VA or 16-volt, 20VA transformer for use with multiple door chimes in one home; order in standard package of six to help assist with your planning and still retain that economical edge Quick install transformers, built to last so you should have fewer call backs One 8 or 16-volt, 20VA transformer needed for a single chime; multiple transformers needed for two chimes cULus Listed for safety, ensuring you have a quality, reliable transformer that will pass inspection