Question

I'm considering building a solar water heater using a 55-gallon drum and 1/2" black plastic tube. Advice?

Asked by Laurie Fox
Alpine, TX

The drum would be filled with water that would be heated by the sun. The black tube would be rolled around the inside of the barrel and contain the supply water. What length of 1/2" black tube would be needed to raise the supply temp. from approx. 52 degrees to the water barrel temp. of approx. 100 degrees? The water pressure is approx. 70 lbs.

Answer

Hello Laurie,

Not to sound pessimistic, but this will not work, for the following reasons.

  1. A 55-gallon drum does not have enough surface area to heat the water and maintain a constant temperature.
  2. The water volume in one chamber (55 gallon barrel) is too great to rapidly heat up when it is lowered by introducing 52-degree water.
  3. The pipe installed carrying the 52-degree water will decrease the water temperature in the barrel.

Use the 55 gallon drum as storage

What you should look into is using the 55-gallon drum as storage.

  • If possible, circulate the water in the 5-gallon drum through black pipe, perhaps laid out on the roof of the house. This will rapidly heat and transfer the heated water to the 55 gallon drum.
  • Next, run your coil of pipe in the drum that contains the water you wish to heat.
  • Now to meet plumbing code and protect you from illness, you will be required to use a double-walled pipe so that the non-potable water in the barrel does not enter or mix with the potable water on the domestic supply side being heated.

The key to properly designing a system is your ability to control the flow of water to increase the heat transfer. You’ll want to install thermostats on the incoming water in the 55-gallon drum and on both the incoming and outgoing lines for the water which you intend to heat.

Also, you will want to install valves or pumps with multiple speed settings. This is so you can commission the system (study temperature rise and reduction) to achieve the greatest heat transfer. By slowing down or speeding up the flow of water in both the 55-gallon drum and domestic system, you will be able to increase the change in temperature.

Look into commercially designed systems, too

I wish you great success in your quest, and would suggest that you also look into commercially designed and sold systems.

  • These systems can receive federal, state and local tax incentives and grants, lowering your costs and time.
  • Also, they have been engineered, tested and will deliver a greater amount of output vs. a home-designed system.

Tagged In: solar water heater

Do you have a question about greening your home? GreenHomeGuide invites you to Ask A Pro. Let our network of experienced green building professionals – architects, designers, contractors, electricians, energy experts, landscapers, tile & stone specialists, and more – help you find the right solution.