One of the things that uses up the most energy in a home is hot water. And all of that heat is wasted as it drains away into the sewage system. The EcoDrain device pictured above allows you to partially warm up incoming cold water with the heat from the outgoing hot. It’s a heat-exchange system, and isn’t exactly a new invention, although unlike most other solutions can be installed horizontally. This allows it to be placed “under the bathroom floor immediately adjacent to the drain, thus catching the waste water at its hottest.” It won’t be enough to get the incoming cold up to a good steamy temp, but it’ll help you use less hot water mixed in, thus saving you money. It requires no electricity, and has no moving parts; once installed you can just forget its there. “It’s priced at US$439.95, and is claimed to offer a return on investment ranging from 17 to 43 percent per year – based on the energy costs in various American cities.” Or in other words, you’ll be able to shower for about 33% longer while using the same amount of power you would have without the EcoDrain.