It’s human nature to keep using old equipment as long as it’s functional, but there comes a point when it’s more cost-effective to replace it.
For example, imagine that your furnace is 20 years old. It still heats the home, so no need to replace it, right? Not exactly.
If your furnace happens to fail on the coldest day of the year, then you’re going to have to pay the high price of the first contractor you can get to show up. Get competitive bids before the furnace fails and you’ll save money.
Additionally, each year you keep that old, inefficient furnace running, it’s costing more to operate than the newer generation of furnaces. Even if that old, worn out furnace is still operationational, it may not be safe (be sure to have a carbon monoxide detector on each floor of your home).
And regarding your good old water heater – eventually they all leak. Consider replacing any water heater that’s more than about 12 years old, especially if it’s located in an attic or someplace else where a leak may cause serious damage.