ah, you want this, which also exists: https://www.finehomebuilding.com/2013/03/07/hot-water-circulation-loops https://www.finehomebuilding.com/2013/03/07/hot-wa

ah, you want this, which also exists: https://www.finehomebuilding.com/2013/03/07/hot-water-circulation-loops https://www.finehomebuilding.com/2013/03/07/hot-water-circul... the way I do it is just turn the shower on about 30 seconds before I get in, which works the same with half the piping and less energy loss due to circulating hot water (but some water loss)