Reuse heat going down the drain?
Like most of us in the world, I like to take a warm shower no matter what time of year it is. It seems that the colder it is outside, the warmer I like to have the temperature of my shower. As I stand there letting the water rush over me and contemplate the mysteries of life, warm water goes down the drain, warming up the pipes going to the sewage treatment facility. I could go on and on about using various products, or sharing a shower to save water, but thats not the purpose of this article.
Even if you like to take a quick “cold shower” during the summer, I don’t know of anyone who only turns on the cold side of the faucet. That water straight out of the cold tap can be quite cold during the winter or barely cooler than room temperature in the summer (depending on the underground temperature in your area). If you decide to barely turn on the warm water to take the nip off your cold shower, there is some heat that is still wasted down the drain. I’m not the only one (or at least I hope not) who has stood there in the shower thinking about a way to recover this heat. It seems the way to do this is to have a heat exchanger draw off as much heat as possible from the water going through the drain pipe. This way, we are saving money and energy without any lifestyle changes.
I looked up some products that I could purchase to help with this issue and found some that were quite pricey. There are many different styles of heat exchangers, and they would of course do the job, but I like to do things myself to save a little whenever I can. I found a few videos and websites that explained how heat exchangers work and how to make them. Most used copper to copper piping to transfer the heat. Since I’m not a plumber and don’t have much experience with soldering copper pipes together, I needed a different approach. Luckily, I found this video from Rob the Plumber explaining how to make the same heat exchanger with 85% cheaper parts (half of the parts are PVC). Using the PVC parts on the outside aids in insulating the water from loosing the precious heat that it just recovered.
Obviously, the larger the outside PVC recovery pipe is, the more contact the copper drain pipe has, resulting in more heat recovery. Use this template and scale up as much as you need. You can then connect the incoming cold water and out going heated water in different ways. One option is to route the cold water that normally would go straight to the shower through the heat exchanger first to recover the heat and use it instantly. This will cause you to use less hot water since the cold water isn’t cooling it down as much. Another option is to route the heated water back to the cold water intake on the water heater. The water heater doesn’t have to work as hard since the incoming water isn’t as cold. This helps out in the life of the water heater and gives a faster heating time for all the other things that use hot water. Personally, I would use the first option for the shower and sinks (instant gratification) and use the other option for devices like a dishwasher or washing machine. The nice thing about this device is, in most cases, you can install this in your home! You are not limited to building a new house to take advantage of this.
Image Credit: Heat Exchanger Diagram