Typically, there are two types of water circuit in a domestic residence, as follows:

Indirect or Closed Hot Water circuit

A sealed system, often referred to as the “central heating” and onto which any towel warmer can be installed regardless of the material from which it is manufactured. Closed or sealed systems should contain a BS7593 corrosion inhibitor required to maintain both the system and the towel warmer as failure to do so could result in corrosion or even failure.

Direct or Open Hot Water circuit

An open system is fed directly from the main water supply which is then heated most typically by a boiler and then distributed throughout the house to the taps, bath, shower etc. and to the appliances (e.g., washing machine) onto which only towel warmers manufactured totally from brass or stainless steel can be installed. Any model made from or consisting of ferrous metal (steel) components cannot be installed on a Direct/Open circuit.

CAUTION: when a brass unit is installed in conjunction with some water softeners there can be a risk of dezincification.This may occur because aggressive chemicals within the softened water can attack the zinc content ofthe brass causing the composition of the tubing to breakdown and eventually leak.