[MBlume]

The author refers to no metrics at all other than their invented one (the hot water rectangle) and then makes no attempt to motivate it by connecting it with something someone living in the home might care about. Does a smaller hot water rectangle mean less energy consumed? Faster hot water at the tap? Hotter water at the tap in steady state? Would other interventions (insulation on the pipes, say) improve these metrics at lower cost? We don't know.

[throw0101b]

> Would other interventions (insulation on the pipes, say) improve these metrics at lower cost? We don't know.

There is a "Related Articles" section that goes into facets of the topic. This is published in Green Building Advisor, and the audience would have some knowledge about various aspects of building science and efficiency. The publication is not strictly aimed at home owners.

A lot of times by the time the designs get to a general contractor or plumber they're already fairly baked. The placement of various rooms (kitchen, bath, powder, laundry, etc) is one of the first orders of business, and it's an easy way to have designers/architects think of layout without getting into the plumbing details (home-run, race/speedway).

User training for this metric ends up being easy: draw a box, smaller is better. No need to get into things like plumbing architecture, materials, labour, etc.

[regularfry]

If you know the rectangle then you know something about the minimum possible length of pipe. If heat loss is proportional to total pipe length, it gives you an order of magnitude for the total.

[friend_and_foe]

OK, but what toes that have to do with dividing the area traced by the pipe with the floor area of the place?

[regularfry]

That gives you a ratio that you can compare between properties.