Do you throw the heat from you dishwasher, clothes washer and shower down the drain? Dishwashers use very hot water that you pay to heat. You likely wash your white clothes in hot or warm water and throw that heat down the drain. Your water heater uses energy that you pay for to heat it up that water.
At my house the “cold” water that is piped into the house is about 50 degrees F (10C). Give or take a few degrees. I do not like taking a shower in 50-degree water. I pay good money to have it at a warm temperature.
As I soap, rinse and repeat that warm water is running down the drain carrying away the heat I paid for.
Mean while, down in the basement the water heater is taking in 50-degree water and burning natural gas to heat it from 50 up to 130. It takes a lot of energy to heat water up by 80 degrees.
Drain Water Heat Recovery to the rescue
There is a way to get some of the heat out of the drain water and put it to work for you. If your house has a straight section of drainpipe, you can install a Drain Water Heat Recovery unit. Recycling some of the wasted heat is good for your checkbook and good for the environment.
If you have a basement, you likely have a big, plastic or cast iron, pipe that goes straight down to the floor. If you hold your hand on it when someone is taking a shower, you can feel the warmth. By wrapping copper tubing around that main drain line, it can be used to collect some of the waste heat.
By running cold water through the copper tube heat collector, before it goes into the water heater, you can recycle some of the heat. When your heat recovery unit increases the temperature of the water, going to the heater, by a few degrees saves you money. Heat recovery reduces the number of degrees that the heater has to raise the water temperature. That results in an energy savings that will show up as money saved on your utility bill.
I recommend buying one of these
There are, factory made, drain water heat recovery (DHR) units that you can buy. These units are pre-assembled on a section of drainpipe so you will need a contractor to cut out part of your drain line and replace it with the new section that has the DHR unit on it.
The following two links are examples of what is available from Canada.
I have not seen either of these in person, but as an engineer who has worked with heat exchangers, I like the four tubes run in parallel design of Power-Pipe. It is well designed for heat transfer and it makes good sense from a water flow perspective. You have to have good pressure and flow going to a tankless water heater for it to switch on and off correctly.
It does not matter what type of water heater you use. They all benefit from heat recovery.
This is not a quick pay back project because copper and labor are both expensive. You can expect a payback in 3 to 7 years depending on how much heat you waste down the drain. If you use electric power to heat your water, the payback will be a little faster. The savings on a retro fit could be 25 to 35% of your current cost for hot water.
It would be a good idea to hide all that copper under an inch or more of fiberglass insulation. That will hold the rescued heat in where you want it.
Drain Water Heat Recovery units should be standard on all new construction homes. Once installed, they are a low or no maintenance energy saver.
Do a Google search on drain water heat recovery and you be swamped with information. The Google results that I got showed that our friends in Canada are ahead of us in using home drain water heat recovery. Sometimes we Americans are a little slow in putting good ideas to work.
Click here for a free money saving report titled HOW SAVE MONEY ON YOUR NEXT HEATING BILL
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