16 ms·

I don't understand why they talk about it as a rectangle, and not in terms of the total length of pipe? For example, if I arranged everything that used hot wate

by jefftk 3y ago

I don't understand why they talk about it as a rectangle, and not in terms of the total length of pipe? For example, if I arranged everything that used hot water along a single wall of my house, I could have a rectangle of zero area and the maximum score (0%). But there's still a big difference between a version where it is spread out over 5 ft versus 100 ft.

throw0101b 3y ago
> I don't understand why they talk about it as a rectangle, and not in terms of the total length of pipe? Because the total length of pipe is not useful: you could have a one set of pipes going to the kitchen, another to bathroom #1, and another to bathroom #2. * See second diagram: https://www.finehomebuilding.com/project-guides/plumbing/three-designs-for-pex-plumbing-systems https://www.finehomebuilding.com/project-guides/plumbing/thr... * https://www.youtube.com/watch?v=FLhddKA1lfQ https://www.youtube.com/watch?v=FLhddKA1lfQ If the first thing you is take a shower or brush your teeth, you have to run the water to bathroom #1, which heats the water in the pipe. Then you go to the kitchen to make breakfast and then you're starting over all over again because the hot water pipe is filled with cold water, and you have to waste energy filling it. The person that uses bathroom #2 (room mate, child) also has a completely cold hot water supply pipe, so even if the first person wakes up earlier and primes the other two hot water pipes, that doesn't help with the third. That is one design ('home runs' from the heater, through a (PEX) manifold, to each faucet), another is a giant race track (or "speedway"): so the first person that wakes may have a longer wait for hot water, but the entire system is now primed, and hopefully the next person(s) will use it before the hot water cools. * https://www.youtube.com/watch?v=13h0L_GlOlI https://www.youtube.com/watch?v=13h0L_GlOlI But the total length of pipe in either the home-run or the racetrack setup does not help indicate things like priming and piping. But the rectangular metric would take care of both setups, as the length and architecture wouldn't really matter given the short runs. Gary Klein, the person who came up with the metric, has been looking at hot water systems for a few decades, so he's see a few designs in this day, and this metric is a way to easily take into account various ways pipes are run and connected. The metric also quite easy to measure on blueprints as you don't have to try guessing how pipes will be run (up or down walls, through attics or basement, etc): just draw a square in AutoCAD, SketchUp, etc, around all the faucets. No plumbing expertise by the architects required.
- jefftk 3y ago
  Would you at least agree that the rectangular metric is misleading for cases where all the water usage is along a single wall, and so the rectangle has an area of zero? If you want a simple metric the perimeter of the rectangle seems much better than the area to me.
  - throw0101b 3y ago
    How easy is it to get the perimeter of a rectangle versus its area in architectural software? Because 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 them think of layout without getting into the plumbing details (home-run, race/speedway). It also allows for multiple hot water heaters (e.g., in commercial builds), where there are units that serve localized needs. User training for this metric ends up being easy: draw a box, smaller is better.
jmole 3y ago
Yeah this is puzzling to me as well. The only things that matter here, it seems, are length and insulation. If you have a full recirculating system with good insulation, all the water in the pipes will be hot all the time, which is the best way to avoid wasting water while waiting for the hot water to get hot.

by jefftk 3y ago

throw0101b 3y ago

> I don't understand why they talk about it as a rectangle, and not in terms of the total length of pipe? Because the total length of pipe is not useful: you could have a one set of pipes going to the kitchen, another to bathroom #1, and another to bathroom #2. * See second diagram: https://www.finehomebuilding.com/project-guides/plumbing/three-designs-for-pex-plumbing-systems https://www.finehomebuilding.com/project-guides/plumbing/thr... * https://www.youtube.com/watch?v=FLhddKA1lfQ https://www.youtube.com/watch?v=FLhddKA1lfQ If the first thing you is take a shower or brush your teeth, you have to run the water to bathroom #1, which heats the water in the pipe. Then you go to the kitchen to make breakfast and then you're starting over all over again because the hot water pipe is filled with cold water, and you have to waste energy filling it. The person that uses bathroom #2 (room mate, child) also has a completely cold hot water supply pipe, so even if the first person wakes up earlier and primes the other two hot water pipes, that doesn't help with the third. That is one design ('home runs' from the heater, through a (PEX) manifold, to each faucet), another is a giant race track (or "speedway"): so the first person that wakes may have a longer wait for hot water, but the entire system is now primed, and hopefully the next person(s) will use it before the hot water cools. * https://www.youtube.com/watch?v=13h0L_GlOlI https://www.youtube.com/watch?v=13h0L_GlOlI But the total length of pipe in either the home-run or the racetrack setup does not help indicate things like priming and piping. But the rectangular metric would take care of both setups, as the length and architecture wouldn't really matter given the short runs. Gary Klein, the person who came up with the metric, has been looking at hot water systems for a few decades, so he's see a few designs in this day, and this metric is a way to easily take into account various ways pipes are run and connected. The metric also quite easy to measure on blueprints as you don't have to try guessing how pipes will be run (up or down walls, through attics or basement, etc): just draw a square in AutoCAD, SketchUp, etc, around all the faucets. No plumbing expertise by the architects required.

jefftk 3y ago
Would you at least agree that the rectangular metric is misleading for cases where all the water usage is along a single wall, and so the rectangle has an area of zero? If you want a simple metric the perimeter of the rectangle seems much better than the area to me.
- throw0101b 3y ago
  How easy is it to get the perimeter of a rectangle versus its area in architectural software? Because 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 them think of layout without getting into the plumbing details (home-run, race/speedway). It also allows for multiple hot water heaters (e.g., in commercial builds), where there are units that serve localized needs. User training for this metric ends up being easy: draw a box, smaller is better.

jmole 3y ago

Yeah this is puzzling to me as well. The only things that matter here, it seems, are length and insulation. If you have a full recirculating system with good insulation, all the water in the pipes will be hot all the time, which is the best way to avoid wasting water while waiting for the hot water to get hot.