The place I used to work had inventory on hand and so they could do your service now. Most people dont fix something that isn't broken. Meaning, if their existing system works, they won't replace it just because. So what this also means is that speed and time of delivery is very important. If your heat or cooling has broken and it's necessary, and you want to replace it, you're going to want to do it asap. So it needs to be on hand for contractors to have ready to go. Furnaces don't break in the summer when they're not being used.

If you have contractor deals, you're going to have to provide some incentive for them to use these things. Because contractors are inclined to charge the most amount of money for the thing that's easiest for them to install.

I am biased because I worked at a shop whose selling point was "we'll do it now when everyone else will book you two weeks out" and when you're talking about things like water, heat, and to an extent sewage, the value of time increases significantly.