In an article in the Energy Vanguard Blog, I wrote about the plumbing work I did to begin the retrofit of my hot water distribution system (and the lessons I learned!). I’m bypassing the original too-long, too-big copper pipes with shorter, smaller runs of PEX tubing. My goal is to get faster hot water and reduce the amount of water wasted while I wait. Since then, I have finished the three runs I’m changing. And I have some results to share with you.
The existing hot water distribution system
My house was built in 1961 and has a poorly designed hot water distribution system. The schematic below shows the water heater, the trunk line, and the branches to the three fixtures I’ve improved. (The water heater is actually in the basement below, not the foyer. The red dots are the hot water fixtures.) The primary bathroom isn’t really that far from the water heater, as you can see. But the hot water pipes don’t take the most direct route to the lavatory and shower.
The hot water rectangle for my house isn’t as bad as it could be. The water heater is near the middle of the house, and the bathrooms (basement and main floor) are stacked and close to the water heater. The kitchen is pretty far away, and the laundry room is farther. The hot water rectangle is 50%, which is bad for a two-story house.
The hot water rectangle is just one part of the problem. That indicates the fixtures and water heater are spread out so the pipes are longer than they could be. The other issue is that the pipes are too big. The trunk line is 3/4″ copper all the way to the kitchen. The branches are 1/2″ copper. That’s a lot of water in the pipes that gets in the way of the hot water traveling to the fixture.
I’m not changing out the whole plumbing system (not yet anyway), but I’m fixing three of the most used fixtures: the shower and lavatory in the primary bathroom and the kitchen faucet. I built and installed a manifold that lets me run three PEX tubing lines to those fixtures. And now I’ve got my two bathroom fixtures fixed.
The schematic below shows the new runs for those two fixtures. Both now are served by shorter, smaller pipes with a lot less water in them. I could have made the lavatory run even shorter if I had rotated the manifold 180°, but that didn’t occur to me until I made the sketch here.
If you look carefully at those two schematics above, you can see that the lengths of the shower and kitchen hot water pipes are far shorter after the retrofit. I couldn’t get as much length reduction from the lavatory, but the reduction in pipe size still improved performance dramatically.
I tested all three of those fixtures for time to hot water and the amount of water wasted while waiting. I did the testing when there had been no hot water call for at least 8 hours, usually first thing in the morning. Here’s a summary of the before and after numbers:
I cut both the length and diameter of these three runs, and that resulted in much better performance. The earlier article showed the lavatory and shower results, but the kitchen sink numbers are new. The volume calculations for all three are also new. I completed that kitchen run about a month after the other two, at the end of August.
One thing to note here is that the volumes shown above aren’t the whole volume between the water heater and the fixture for each run. They’re the approximate volumes affected by the retrofit. There’s still a few feet of 3/4-in. copper pipe at the water heater and the manifold and also a few feet of 1/2-in. copper pipe connecting the new PEX line to the fixture.
To give you a little more perspective, the table below shows the percent reduction in the volume of water in the pipes and the time I wait for the hot water to arrive.
As you might suspect, I’m quite pleased with how this has turned out. That’s not instant hot water, but it’s a huge improvement. With this improvement, I actually use the hot water in the lavatory sometimes. It also means that I won’t have to turn on the lavatory and bathtub hot water faucets at the same time as the shower to speed the hot water along. Yay!
I still have room to improve upon those numbers. The majority of the volume of water is in the vertical pipe from the water heater to the manifold and in the manifold itself (photo just above). I’ve got those pipes mostly insulated now (see lead image), but there are still some gaps. If I go nuts on insulating and air-sealing around those pipes, I’m hoping the water in there will stay hot.
There you have it. Getting faster hot water is a matter of reducing the length and diameter of the hot water pipes. I used two 1/4-in. PEX lines here, but you need to be careful in sizing your pipe if you do this. Going all the way down to 1/4 in. works for runs less than about 25 ft. long and only if you have enough pressure. See my article on my friend David Wasserman’s hot water retrofit for more details.
And yes, another way to get hot water would be to use a recirculation system. If you go that route, choose the demand type system, not the continuous. Even on a timer, the continuous recirculation system uses far more energy than the demand system.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has written a book on building science. You can follow him on Twitter at @EnergyVanguard.
Get building science and energy efficiency advice, plus special offers, in your inbox.