A lot of people think of heaters in terms of “bigger is better.” This is true, in the sense that larger heaters do have a greater heat output. It is not true, however, that a larger heater is always a better option. After all, if you follow that logic you end up with a commercial heater larger than your basement. In all seriousness, though, a heater absolutely must be properly sized to fit the home in which it is being installed. Let’s take a look at what can happen if you pick the wrong sized heater, either too large or too small.
A heater that is too large tends to provoke one major problem, by putting out more heat than the rest of the system is used to. That major problem is short-cycling. Short-cycling is what happens when your heater rapidly turns itself on and off throughout the day. This is caused by the heater’s limit switch, which is designed to monitor the internal temperature of the heater. When the heater’s internal temperature gets above the safety limit, the limit switch shuts the system down to prevent it from overheating. After the heater cools off, it starts up again and provokes the same reaction. This locks the system into a never-ending cycle of on and off that wastes energy and damages the system. Now, the oversized heater isn’t actually overheating, but its heat output is high enough to provoke the limit switch anyway.
A heater that is not large enough for the home it’s supposed to be heating will still have a much shorter lifespan, though not from short-cycling. Instead, an undersized heater will simply run indefinitely in an attempt to heat a space that it does not have the output to adequately service. The stress of constantly being on will wear down the heater much faster than one which is properly sized, eventually causing the system to die an early death and require replacement.