Hey! I am an HVAC+R tech, commercial/residential scope. I can honestly tell you nobody's HVAC will fail during regular hours. Most furnaces fail on the first -18°C night, and A/C always fail on the hotest days of the year (even if it was "fixed" last cooling season). And one certainty I have found in this industry, if the weather is insane (storms, +30° heatwave, -40° cold snap) I'll be outside on a rooftop, fully exposed to the elements, fixing something that should have been addressed months ago. Regular maintenance & repairs can avoid 80% of failures, but industry needs to step up their quality of manufacture for equipment. Residential systems need to be built to spec, code, & SMACNA/ASHRAE standards. Not built to budget, and please dear god we need "builder spec" to get up to speed with modern equipment & standards! Rule of thumb is going the way of the Dodo bird.