The Company we visited yesterday told us that many installers will insist on a liner when it isn't required. A smoke test should be done anyway, to check for good smoke 'pull', before an order is placed. Our house being 1960s should not require a liner as the chimney is probably clay lined.
Under Building Regs. a carbon monoxide monitor/alarm is a Legal Requirement, as is an Air brick if the heater is over a certain wattage.