The answer can be confusing if you are asking yourself what size of hot water system is suitable in your home.
Some manufacturers determine the answer by assuming that you will be consuming more water than your actual usage would indicate, while others will tell you it is based on the number of people in your household or the number of bathrooms in the home. Buying a larger system than is actually needed can cost extra yet unnecessary money, although many homeowners do that due to the confusion.
Factors to Consider
The key to the size of hot water system is the number of people in your household along with when and how they will be using the hot water. Ask yourself whether the washing machine or dishwasher are typically run at the same time as people are showering, whether people use more water by taking a bath instead of a shower, and whether your showers have a standard showerhead or the more energy efficient WELS 3 Star rated.
The typical shower lasts between 5 and 10 minutes but consumes the most hot water in the typical home. You can save water and energy as well as reduce the size of the required hot water system by using a WELS (Water Efficiency Labelling and Standards) 3 star rated showerhead. Assuming you have the 3 star showerhead and that a family of four takes an 8 minute shower each using a mix of hot and cold water, about 224 liters would be used by that family.
Even if the family take separate showers at the same time, a hot water system with a capacity of 224 liters would be adequate, assuming that all the family take their showers during the morning. However, the recovery time of the system would then need to be reckoned in to the equation, if more hot water was being used after the showers, or you often have other people in the home.
Off Peak Electricity Issues
To avoid running out of hot water during the day, you may need to install a larger off peak electric storage unit, as these are designed to only heat your water at night. You would have to purchase a larger tank, although that cost would be offset to some extent by the savings on off peak electricity.
An Example of Tankless Hot Water
The number of showers being taken at the same time would affect the flow rate needed if you purchase a Bosch 21e tankless gas hot water system. If no other appliances in your home are being run at the same time, and there are three of you all taking a shower at the same time, a flow rate of 21L/min or higher would be needed. A lower flow rate of 14L/min would be adequate if only two of you routinely took a shower at the same time. One of the advantages of using a continuous flow unit is that you always have hot water available to use, regardless of how much you are using the system as there is no recovery time needed.