Getting a hot shower in your remote off grid home when its five degrees Fahrenheit outside is priceless. If your water is stored above ground in a cistern, it will be more difficult than pumping it from a well on demand. Your cistern can get a frozen layer of ice, that will hold water as cold as 28F at the bottom. It takes a lot of energy to warm this to 100F for a comfortable shower.
All too often I’ve had a great plan for something that later had unforeseen consequences. In our case this happened wit the water system and hot water. The situation arises because of 2 early choices on our remote home:
- The decision to keep the deep well pump that required 240Vac when moving here. There were other expensive pumps available for solar applications, but cost drove the decision to keep the working pump and system in service. Inverters can be slaved together to run the well on batteries if necessary, but normally we run the generator 5-6 hours every 5-6 weeks to fill the cistern.
- The decision to purchase a large 3000 gallon poly tank and keep it above ground. We piled some straw bales around it, but it still freezes. Being above ground in the winter means it can get a layer of ice a foot or two thick, but it causes no problems as long as we keep it properly topped off.
We have a wonderful on-demand propane powered hot water heater. It has worked wonderfully for years. On-demand water heaters are rated by how much they can raise the temperature of the water running through them, in our case this is about 50F. This is where the problem lies.
When there’s a cold snap for a week or more, our cistern gets a nice layer of ice. We draw water from near the bottom of the tank where the temperature is as cold as 28F. As this water is pumped through the on-demand hot water heater, it exits at 78F, and probably cools a little through the pipes on its way to the shower. 76F may be a comfortable swimming pool temperature, but it sure seems to be a cold shower!
| Side Note: Why 28F ?
When water freezes, it starts on the surface and grows thicker downward. The water below is colder than 32 degrees. Water at 28 degrees is heavier than ice, and that’s how the fish make it in a frozen river. |
My solution this last fall was to put a secondary 30 gallon tank in the kitchen. The idea was that we’d have 30 gallons at 50F or warmer in the kitchen to feed the hot water heater with. I purchased pressure tank and ever so carefully plumbed it in. (Hate to open up the pressure side of plumbing, its so hard to get all the water and leaks stuffed back in!)
Unfortunately, this did not work as expected. The pressure tank 
just has one opening at the bottom only. Water doesn’t flow through it very well. As far as showers are concerned I’m glad this was a mild winter. The next project for this will be to do some machine work on the tank and create a water inlet near the top of the tank. Water comes from the cistern to the top of the secondary tank and gets pulled off the bottom of it for the water heater. Always plenty of projects!
Lessons learned:
- On-demand hot water heaters work well with earth temperature(underground) water as a source.
- If you’re going to store water in a cistern, always bury it if possible!
This Fall we’ll return to this project and provide an update on the modified indoor tank performance for hot showers.
Do you have any tricks you use to keep the water hot in the winter? Ways to save electricity or fuel and still have that luxurious hot shower potential? Tell us your suggestions below in the comments!
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