My personal experience, new home (construction completed circa 2017): - MANY design errors, some I spot at project stage, I was told they are not errors, it tu

My personal experience, new home (construction completed circa 2017): - MANY design errors, some I spot at project stage, I was told they are not errors, it turn out I was right; - sizing is an issue because the climate may vary MUCH. Three years ago today in the morning there was -22℃ today +10℃ to be in comfort we need to been able to heat (or cool) in much above/below the average cases, so well... I'm not much against pay for extra margins; - my sanitary hot water heater (Daikin/Rotex M2O EKHHP) break after 5 years, a leak from the sanitary water pipe heat-exchanger, two month for a fix, BUT being provident I've put aside a very small resitive heater classic boiler (50 liters) so I have had exactly ZERO "service interruption", in that case the problem is that something is cheap to back up, something is definitively not... For instance I have one of the first thermodynamic VMC (a double-flux VMC with a heat pump heat exchanger instead of a passive one) and being in a new home I can't stay without a VMC for more then few hours or I have to open the windows no matter the outside temp. Well, I've also choose to have a backup but it's just a passive VMC since spending 4k€ to keep a secondary cold spare it's definitively wasted money. The small resistive water heater was just 150€ in total plumbing materials included, mounted by myself so a reasonable backup. Similarly the main heating (water-water heat pump) have no electrical backup, I've chosen AND I REGRET a small wood stove for modern homes (Jøtul Scan-66) and I keep a bit of wood (used in the spring to cook pizzas outside, so it remain moderately "fresh" since it's renewed any two/three years). I regret because for not much more I've should better chose a wood based boiler and a LARGE insulated reservoir to make hot water in few hours for an entire day and the small p.v. LFP batteries suffice for a pump. Long story short: most technicians do NEVER think about when something goes wrong and most do not even have at their own home the "new" systems they design so they do not really know them beside theory.