Short answer
A booster heater raises the building's hot water to the higher final-rinse temperature a high-temp dishwasher needs to sanitize. Some machines have one built in; others need a separate booster installed beside or under the machine. Low-temp chemical dishwashers sanitize with a chemical instead and do not need one.
A typical building water heater is not set hot enough for a sanitizing rinse, and raising the whole building's supply would waste energy and create a scald risk at every tap. The booster heats only the water going to the dishwasher's rinse.
Boosters are usually electric and often need their own circuit, so check the voltage and amperage on the spec sheet before ordering. The size required depends on the machine and on how hot the incoming water is, which the manufacturer's installation manual sets out.
Updated · By Norpex