How often do you need to replace a hot water heater? While ten is the age at which heater replacement is generally recommended, the actual need to replace a heater could arise before or after this timeline. The list isn't too long, but it's still important. First things first: never pour liquid fats, oils, or grease down the drain. As they cool, they become more solid and cling to the insides of pipes, building up into clog-inducing paste. Avoid the temptation of dumping chemical clog removers down your pipes when dealing with slow or blocked drains.