In my experience tankless water heaters are the way to go in areas with little sun.
In sunny areas, water can act as an energy sink, absorbing excess energy from your solar panels once any batteries are fully topped up.
But in places where that is not an issue, tankless water heaters can be very energy efficient. My own preference is for gravity fed water, ie your water source, such as a rainwater storage tank, is above the location of the tankless water heater. That way you are not relying on pumps to push the water through the heater, as that requires another energy supply, as the following Q&A from a Winnipeg newspaper shows:
Reader’s Question: We have a propane tank which runs our fridge, stove and a Bosch tankless water heater. The water comes from a submersible pump which is powered through our solar panels through an inverter. The water is pumped to a pressurized bladder that sits beneath the cabin. When we turn on the water, the flow lights the propane, which then should produce never-out hot water. We were told by the propane people that we weren’t getting enough propane, so they increased the lumen of the line to the hot water tank. That had no effect. We occasionally get hot water, but it is inconsistent, and can cut out in mid-shower.
Do you have any experience with these, or suggestions? Apparently they use them all over Europe without problem.
— Ira Ripstein
ANSWER: It is interesting to hear from a cabin owner without the need to connect to the local electrical utility. I have received many inquiries about tankless water heaters.
I commend you for your progressive attitude and attempt to minimize the environmental impact of your summer home by using several energy-saving technologies while still maintaining the amenities of a modern residence. For those readers that have not heard of these systems, a tankless water heater is a small unit that is normally mounted on a wall. It heats cold water on demand rather than holding preheated water in a large tank. Because there is no large reservoir filled with hot water, which cools and requires periodic reheating when not in use, it can significantly reduce the amount of energy required to heat water for domestic use. There are electric units and those that use natural gas or propane for an energy source.
After reviewing installation and maintenance information from a few manufacturers of tankless water heaters, I have narrowed down a few possibilities for your lack of hot water. Malfunction of these units can be attributed to one of three main causes; mechanical failure, gas input issues, or water supply defects. Checking for the first possibility will normally require inspection and servicing by a plumber or HVAC technician familiar with these components. Based on your inquiry, I assume that has already been done, so we will concentrate on the other possibilities.
As stated in an online manual from Bosch relating to gas-fired tankless water heaters, “Correct gas pressure is critical for the optimum operation of this heater. Gas piping must be sized to provide the required pressure at the maximum output of the heater while all the other gas appliances are in operation. Gas pressures lower than 10.5″ W.C. for LP Gas will result in insufficient degree rise to the hot water being used and must be corrected.” I would double check with the propane people to ensure the repairs they have done meet this standard. Alternatively, there is a straightforward pressure-testing procedure outlined in the installation manual that could be done by a licensed HVAC contractor to ensure your propane supply is adequate.
If these first two possibilities are ruled out, the final item to check is the water supply. Anyone who has owned a property with a private well and pump, including me, knows there can be periodic issues with consistent water pressure and volume. This may be due to the well itself, but is more often due to damage, wear or improper setup of water-supply equipment. Pumps, pressure tanks and water-supply pipes can wear out, freeze or leak under normal conditions. Because of this, regular inspection and maintenance is critical to proper operation of your water heater. As per online instructions, “The minimum water pressure for the home should be 30psi or greater. For installation on a private well system with use of a pressure tank, the lowest pressure range setting recommended is 30-50 psi.”
Regular maintenance recommended by Bosch includes yearly inspection of the water-filter screen, pilot assembly and burner. They recommend lubricating and cleaning the water valve every other year. They recommend rebuilding the water valve and replacement of the orifice on the pilot assembly every three to five years. If your unit is more than two years old and this has not been done, this could be the cause of the limited hot water supply.
Mineral buildup inside the unit from your untreated water is another likely cause of the problem. This issue may also be linked to another common culprit if the temperature setting on the tankless unit is too high. The higher the temperature setting on the unit, the lower the amount of hot water it is able to produce. According to the specifications published, almost twice as much water is available at the minimum temperature setting of 45F, relative to the maximum of 90F. Surprisingly, mineral buildup is not normally a problem at lower temperature settings but can be significant when the heat is turned up. Rather complicated instructions are included in the maintenance information on how to descale your heater with simple household vinegar. This may be the first item to try in improving performance of your device.
Finally, keeping the water temperature near the maximum may cause another problem that is listed as a probable cause for your symptoms. If the water heater burner extinguishes in the middle of your shower, which could be monitored by a second person near the water heater, this may be the reason for the lack of hot water. The water from this appliance “is very hot out of the tap, requiring a lot of cold water to be added with it in order to attain a usable hot water temperature. The addition of too much cold will overpower and slow the flow within the tankless heater, decreasing it below activation point, which shuts off the burners. The end result is nothing but cold water coming out the outlet. In short, clean out the unit by the descaling method provided, then turn down the temperature-control dial to see if that solves the problem. The manual and maintenance information cited can be found at www.globaltowne.com.