Universal water preheater

The design of my universal water preheater is very simple and realistic:

Two hundred feet of orange 5/8" PEX , as the first water to water heat exchanger was installed into the blue 55-gallon plastic barrel. This heat exchanger is connected to the solar collector and filled with fluid (an antifreeze mixture) to make the system worry-free in my cold climate.

I also installed two hundred feet of white 3/4" Sharkbite PEX as the second water to water heat exchanger in the same barrel and connected this coil to my electric water heater. I prefer the Sharkbite PEX, because it's compatible with SharkBite push-fit fittings or barbed fittings and recommended for residential and commercial plumbing applications, including water-supply systems.

The plastic barrel filled with chlorinated water to prevent smell of water (bacterial growth). I added about 16 Oz. of Clorox into my barrel with 55 gallons of water. The 55 gallons of water play role of heat transfer agent.

The 12V DC pump is powered by 15W solar panel with battery This pump force hot fluid to flow through the first heat exchanger. For a smaller coil (heat exchanger) you can use solar circulator. The water in the barrel absorbs heat from this heat exchanger, while cold water, that flows through the second heat exchange, absorbs heat from the warmed water in the barrel.

In my cold climate the temperature in my basement is up to 5ºC (41.0ºF) higher, than temperature of water from my well. The temperature in my basement could rise up to 10ºC (50ºF) during operation of my oil boiler or wood stove. Therefore, normally my water preheater can utilize not only the sun energy thanks to the first water to water heat exchanger, but it can utilize a warm air of my basement too.


- The battery is required, if your circulator needs more start-up power.

- The lower valve ( located between two tees) is closed.

You can use 3/4" X 3/4" FNPT SharkBite push-fit straight connectors with additional 3/4" nipples (see below)

or 3/4" X 3/4" MNPT SharkBite push-fit straight connectors without additional 3/4" nipples:

I did not find 5/8" SharkBite connectors for the orange PEX, therefore I used two 5/8" Barb X 1/2" MIP adapters:

If for some reason you do not need your solar water preheater any more - just simply unscrew two

SharkBite push-fit straight connectors, install two plugs and open the valve located between two tees:

I would recommend to use the Open-Head/Lid drums to easy installation of Sharkbite PEX:

The metal drums are preferable, if you are going to install your water preheater near your wood stove:

In the warm climate you can use a nicely-looking 35-55 gallon Rain Water Collector instead of a simple plastic barrel.

Just install two or three hundred feet of white 3/4" Sharkbite PEX in the Rain Water Collector, filled with chlorinated water and connect this coil to your electric/gas water heater. The dark colors of Rain Water Collectors are preferable.

You can use such approach WITHOUT any additional solar collectors:

Notes and some calculations:

- I think I created very simple and very efficient designs of universal water preheaters, based on the cost-effectiveness ratio.

- normally my electric water heater is covered with a good insulation blanket.

- 8.34 BTU's are required to raise 1 gallon of water 1 degree Fahrenheit.

- 1 kW = 3412.142 BTU/hr.

- In my basement, the 55 gallons of water could be heated in average up to 80°F during operation of my oil boiler or wood stove (without solar collector). That means I can offset roughly about 4 kW of electricity daily: (8.34 BTU's X 55 gallons) x (80°F - 50°F) = 13,761 BTU's.

- When my solar collector in use and plastic barrel is perfectly insulated, the 55 gallons of water could be heated up to 120°F. That means I can offset roughly about 9 Kw of electricity during each sunny day: (8.34 BTU's X 55 gallons) x (120°F - 50°F) = 32,109 BTU's.

But with insulated barrel there is no chance to utilize a warm air of my basement during operation of my oil boiler or wood stove in situation, when my solar collector can not provide any head, because of bad weather condition.

Therefore I decided not to keep insulation on the barrel.

Please note that there are no heat loses in this setup, because all heat unused by my water heater rises to the main floor of my house in the form of hot air. This situation is similar to my main Basement supplemental heating system.

To reduce heat losses I wrapped my electric water heater with Reflectix insulation.