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Old 02-28-16, 07:58 PM   #1
oil pan 4
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Default sewer water heat exchanger

The average temperature of household waste water is typically between 80F and 90F.
All you have to do to figure out how many BTUs you are flushing down the toilet is to get a water bill figure out how many pounds of water you used, subtract ground water temperature from average waste water temperature. Then multiply the temperature differential by pounds of water.
I bet it comes out to be a pretty big number.
What if we could put some of that heat back into the household?
If some one were to live off grid this could massively reduce their water heating requirements and save a lot of propane.

Here is my idea:
Get a good long length of 4 inch, 0.080'' wall 304 stainless steel food grade pipe, because most home poo pipes are 4''. Then take a length of 2.5" or 3" and split it down the middle and weld it on to the bottom of the 4 inch pipe, then weld water line hook ups to the ends of this bulge. So as the warm waste water flows out cool fresh water comes in the waste gives up its heat to fresh water.
I have about 100psi of water pressure so I want 80 wall pipe, if you had well water at a much lower pressure then standard 1/16'' pipe would be fine.
Did I mention that I may try to build this?

To build this you need lots of 4 and 2.5 or 3 inch pipe.
I have been told this 4 inch 80 wall pipe runs upwards of $20 per foot retail prices and 2 or 3 feet isn't going to be enough, this is a heat exchanger so it has to be long, as long as possible.
Lucky for me I can get a lot of pipe and cheap as dirt from the scrap yard. I already have about 40 feet of food grade stainless 2.5 inch pipe I have some 0.080'' wall 4 inch pipe but its slated for another project, I should be able to get a lot more.

I don't have to use 0.080 wall pipe but I kind of want to.

Other hazards to look out for:
When you weld stainless in the presence of oxygen you can create hexavalent chromium if you don't know what you are doing. If you don't know already what hex chrome is then you should not be trying this.
The welds have to be air tight.

Last edited by oil pan 4; 02-28-16 at 09:40 PM..
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heat exchanger, heat recovery, preheater, waste heat, water heater

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