Multiple units are common for a large house. Not because they want a backup but because there are limits to how many square feet a single home unit can handle. Having a 2nd story or basement can influence the decision too. It’s often cheaper to put in two home units vs upgrading to a large industrial size like what a store might use.
Obviously if you have 2 then one is a backup when you have a problem, but most people aren’t going to have that.
Multiple units are common for a large house. Not because they want a backup but because there are limits to how many square feet a single home unit can handle. Having a 2nd story or basement can influence the decision too. It’s often cheaper to put in two home units vs upgrading to a large industrial size like what a store might use.
Obviously if you have 2 then one is a backup when you have a problem, but most people aren’t going to have that.