Newbie here, have been reading through threads for the past couple of days. I have noticed a common response to questions like "what brand A/C (and/or heater) is better/best?" I see many responses say that 'the install' is as important as the equipment. Could someone please explain what significant aspects of the installation are so critical? I know little about HVAC, so if technical, I ask that you please 'dumb it down' a bit.

Not that it probably makes much difference, but I have a 1995 Rheem outdoor unit and a Weather King oil burner of the same year. House was built in 1995 - I am the original owner. Guessing these were builder grade but don't know for sure. I have had 0 problems with either unit in the 17 years they have been running. Burner gets yearly service, A/C has not been touched since install. I'd like to get a replacement system installed before the outdoor unit takes a dump and I am forced to make a quick, uneducated decision about what to replace the HVAC system with. Only issue I have with both the outdoor unit and the burner are noise......... but the outdoor is located right near a corner of the house (which may amplify noise inside house?) and the oil burner has a Side-Shot (no chimney)...... so there may not be a simple fix to either. thx.