Our morning showers would definitely not be the same without them. We sure miss them when they fail or run out of gas. Our water heaters are usually the silent worker in the back of the house; sometimes they are tucked away where we cannot see them. However they are a vital part of our plumbing system.
Most homes here in Mexico use gas to heat the water and rarely do we see electric heaters. Typically, they are tank-style heaters, which heat up a tank of water so that the hot water is ready at whatever time we need it. The volume of water in the tank is dependent on the demand or requirement of water for the house. Many two-bathroom homes will have tank water heaters with a minimal capacity of 60 to 80 litres (16 to 21 U.S. gallons) of water. However some homeowners will require bigger tanks depending on the higher demand of large tubs, large washing machines, dishwashers, longer showers, etc. Tank water heaters have a limit as to how much hot water can be used, and eventually the hot water will cool off as the tank empties. Hence the tank requires a recovery time to heat up the new volume of cool water that has entered the tank. Depending on heater’s manufacturer, size and configuration, it usually takes between 20 and 60 minutes.
In masonry buildings with pipes – whether they are open over a roof or hidden in walls and floors – there can be heat loss over the length of pipe, which can delay the arrival of hot water to the shower or sink. This heat loss can cause a waste of time and water while you wait for the hot water to arrive. One key factor is the distance between the water heater and the sink or shower where the hot water is being used. If this distance can be minimized, the heat loss or time/water wasted can be lessened. In some cases, clients have installed more than one water heater to shorten the distance between the source and use to help eliminated the losses and increase the duration of hot water availability.
Some homeowners are considering changing their tank-style heaters to demand-style heater (tank-less system). The advantage of a demand-style heater is that it eliminates the need to keep a large volume of water hot. Because it heats the water only when it is actually needed, it is slightly more energy efficient. When there is a demand for hot water, the demand-style heater will heat the water as it flows through the heater, giving it its name in Spanish – calentador de paso. With this kind of heater, hot water can be produced continuously, in theory, forever, or at least until the gas runs out. The heat gained by the water is dependent on various criteria, including the water flow rate through the heater, the size of the pipes in its heat exchanger, and the amount of heat produced inside the water heater.
The size of the demand heater is an important factor to consider. The maximum number of litres per minute the demand heater can produce defines it desired size. Units with higher flow rates have greater heating capacity, which is defined by kilowatts or BTUs. One of the popular sizes offers a capacity of eight litres per minute. Hence the maximum number of litres per minute is defined as a flow rate. If the water flowing out of the heater exceeds eight liters per minute, the water cannot be heater quickly enough to become hot and usable in the bathroom, laundry, etc. A flow rate of eight litres per minute is like pouring a cup of coffee every two seconds.
One problem I consistently see with homeowners who use demand-style heaters is this. The homeowner will use a higher flow rate of hot water than the water heater is capable of producing. For example, while filling the bathtub, the water flow rate was set at a greater capacity than the demand-style water heater could handle and the client was frustrated with cool to lukewarm water for their bath. We solved the problem by lowering the flow rate to a volume of water that could be heated sufficiently, slightly slower than the maximum capability. If the flow rate is not satisfactory, likely the demand heater size is not sufficient for its use. Typical bathtub users will need a demand-style heater with a capacity of approximately 16 litres per minute to handle the higher rate of flow to fill the tub.