apartment therapy changing the world, one room at a time

Something seems funny about the set-up in the diagram. For cost savings it should be pre-mixing the water going into the hot water tank, not at the shower location. The water coming out of the water heater to your shower is already heated to 140degrees. The mixing valve at the shower introduces cold water (50degrees) to cool the temperature of the water down, so you don't scald yourself. Unless you never want ice-cold water coming out of your taps.... The diagram needs to be re-drawn to accurately depict a cost savings.

I was thinking the same thing when looking at the diagram, but then I realized, if it really does work you can turn down your hot water heater... thus saving energy/money.

New Belgium Brewery uses a similar concept on their boilers to reduce their energy costs. I would love RN or AT to test this item.

SoSue - Actually the diagram is demonstrating just one of 3 ways to configure the setup - the preheated water can either be sent to the water heater, shower mixer, or both. The most efficient way would be to send it directly to the shower head so heat loss is minimized.

In terms of the cold water issues - that is really a non issue. The whole point is that the heat exchanger uses hot water going down the drain to preheat the cold water. If you only want to use cold water, then you just turn on the cold water, and then only cold water is running down the drain and through the heat exchanger.

Likewise, if you want hot water, then hot water runs down the drain through the heat exchanger, back to the shower mixer and then less hot water is needed from the water heater...

Joshish - it would be awesome to test this item, maybe if we had a reader who was building new, or remodeling their bathroom who wanted to try it out... I can say that we use the alternate copper coil method on all of my office's new construction and remodel projects and it works. It's and incredibly low-tech, no-brainer option to save energy.

Seems like this would work incredibly well if paired with an on-demand hot water system. You'd see a big boost in efficiency as your shower went on, which is good for multi-family units when everyone wants to take a shower at the same time in the morning.

In a hot water tank unit, some of the efficiency would come from turning down the water heater, or being able to have a smaller one.

I agree with the author, though, I think the retrofitting here would be incredibly expensive, but for a gut reno or new construction, it seems like a very simple and clever way to decrease your costs a lot over the long-term while increasing your comfort.

Rachelw, thanks for the explanation, it took me awhile to grasp the concept. This makes more sense now.