Earlier quoted context omitted.
Any rackmount server will be a nuisance. I ran rack servers at home for years but recently replaced my servers with ATX form factor machines, which are super quiet, ventilate much better and still stack nicely. There are plenty of ATX Xeon motherboards that support ECC ram.
a 4U rackmount server is identical form-factor to a 19" tall tower.
I’ve had good luck using horizontal Silverstone ATX cases with fans on three sides. That said, I’m sure there are 4U units that offer huge but low rpm fans that would satisfy the bedroom server-lab niche market.