This homemade PEX heat coil exchanger DIY project is all about heating water within the large pex coils as it is pushed through on a constant rotating cycle.
It can be used in appliances, tools or projects that uses intake water such as hot tubs, showers, dishwashers, washing machines, heating a swimming pool or sauna and stem heat.

The waters can be kept separate between a wall to keep them from mixing. The flow in three different ways: parallel, counter, and cross.
The homemade heat exchanger should be 4′ x 4′ x 6′. First, make a frame that can coil up toan inchof PEX tubing while having an inch of spacing in the loops.
Use another inch of PVC between the coils going both ways and tie them with polypropylene made string because it can handle all of the heat and power that flows in between. The coil should be 32.5 in.x 32.5 in. for the 300 inches of PEX. Place the three coils inside the other from the bottom up, then down, and then back up again.
Next, get vertical tubes to get hot water flowing to the bottom along one side and then getout the cold water from the bottom on the other side with a tube that runs down along the vertical PVC. Use some PVC elbows to maintain an inch of space from under the coils. The pump required should have a 14-foot head, 5-7 gallons per minute, sustain up 160-degrees F, and have a direct current of 12-24 Volts. It’s a case of trial-and-error, but it will be installment in the house.
Click here to read about how to build a Homemade PEX Large Coil Heat Exchanger DIY Project:
http://www.builditsolar.com/Projects/SpaceHeating/PEXHX/PEXCoilHX.htm