I'm amazed at how little district heating is used in northern climates like Canada and the northern US. In dense areas, district heating using waste heat from power plants should really be required by urban planners, or at least it would make a huge carbon footprint difference if we invest in it.
On an individual household scale, I've always wondered why nobody has come up with basic drain heat exchangers to capture most of the heat coming out of shower and washing machine wastewater before it leaves the building. (Edit: I guess they do exist - https://www.homedepot.com/p/Power-Pipe-4-in-x-48-in-Drain-Wa... - but I've never seen one in the wild)
On an individual household scale, I've always wondered why nobody has come up with basic drain heat exchangers to capture most of the heat coming out of shower and washing machine wastewater before it leaves the building. (Edit: I guess they do exist - https://www.homedepot.com/p/Power-Pipe-4-in-x-48-in-Drain-Wa... - but I've never seen one in the wild)