Bonus topic near and dear to my heart: Ducting design is a biggie, but a neglected issue, and the biggest sin I see in residential HVAC, is ignoring a design's peak heating or cooling energy demands and installing oversized heat pumps.
The bigger is better mentality in that area results in (sometimes dramatically) shorter run cycles with an unnecessarily large compressor. It's not good for your electric bill or the equipment, and you get a monster motor dimming your lights every 10 minutes.
If I had a dollar for every time an HVAC contractor offered me a quote including an upgrade option for a heat pump three times larger than is needed...
The bigger is better mentality in that area results in (sometimes dramatically) shorter run cycles with an unnecessarily large compressor. It's not good for your electric bill or the equipment, and you get a monster motor dimming your lights every 10 minutes.
If I had a dollar for every time an HVAC contractor offered me a quote including an upgrade option for a heat pump three times larger than is needed...