The thicker the scale on the heat exchangers the more energy (OIL GAS OR ELECTRICITY) will be used.
Why would anyone in a hard water area NOT install a Little Plumber because not only will it prevent new scale but it also removes the existing scale, improving heating efficiency by so much that I have known people who have had to turn down their thermostats!
I keep being asked by customers if they have to install their LP units on the rising main. NO they can fit the unit anywhere as the conditioning effect travels upstream and downstream.