Choosing the capacity of an electric water heater seems easy… until you start looking for models and you find tanks of 30, 50, 80, 100, 150 or 200 liters, each with a label promising plenty of hot water, and even so it happens that you fall short (and you shower in a hurry), or you go overboard (and end up paying extra on the bill). Therefore, to do it right, let us see how to choose the capacity of an electric water heater with practical criteria.
Factors that influence the capacity for the electric water heater
In practice, what dictates is the tank capacity and usual use. And, in the background, enter the power and the type of resistance.
Capacity and usual use
Capacity (liters) determines how much hot water you can have at once. But beware, the water heater does not deliver 50 liters of boiling water. It delivers hot water that mixes with cold water in the shower or tap. Therefore, a water heater can yield more than it seems… or less, if you like to shower with the water almost at spa temperature. Capacity is influenced by:
- Number of people at home (and if they shower back to back).
- Type of use: only shower? shower plus sink? washbasins, kitchen, several bathrooms?
- Habits: quick vs long showers; very hot vs warm water.
- Time availability: if consumption is concentrated at the same time at home (mornings), you will need more liters or better management.
Power and resistance
Power does not make the water heater have more water; it makes it heat up sooner. On the other hand, the resistance can be shielded (in contact with the water) or sheathed or ceramic (less calcification and more durable in hard waters). In short, if you doubt between two capacities, prioritize capacity by use. Power helps recover temperature, but does not replace a tank that is too small.
Choosing the power of an electric water heater
Power usually ranges between 1000 W and 2500 W (and some models go higher). Thus, more power, faster recovery, since the water heater reheats the water sooner; Less power, it will go slower, but nothing happens if the use is moderate.
The important thing in a typical home is that choosing more power does not always reduce the expense. In fact, the final consumption depends above all on the heated liters, the target temperature and the losses for maintaining the hot water. Therefore this would be the power you should choose:
- 1200 to 1500 W, being sufficient for moderate uses and small to medium water heaters. Less demanding with the electrical installation.
- 1800 to 2000 W, a fairly good balance for water heaters between 80 to 100L.
- 2200 to 2500 W. Useful if there are several consecutive uses or if you want to recover heat faster, but check contracted power and wiring.
Recommended capacity for an electric water heater
| Capacity (L) | Recommended usual use | Number of people (guideline) |
|---|---|---|
| 10 L | Point washbasin or sink (very occasional use). Not recommended for shower. | 1 (support only) |
| 15 L | Washbasin plus kitchen with moderate use. Shower only if it is very short and with very warm mixture (not ideal). | 1 (partial use) |
| 30 L | 1 short daily shower plus washbasin. Ideal for a studio or second home. | 1 |
| 50 L | 1 to 2 showers (if they are not long) plus washbasin uses. Good for a small apartment with controlled consumption. | 1 to 2 |
| 80 L | 2 consecutive showers with margin plus washbasin and some kitchen. Or 3 showers if they are fast and spaced out. | 2 to 3 |
| 100 L | 3 regular showers without rushing plus normal use of washbasins and kitchen. Good size for small families. | 3 |
| 150 L | 4 consecutive showers with good margin plus distributed consumption (washbasins and kitchen). Recommended if there are concentrated schedules. | 4 |
| 200 L | Large family or high consumption (long showers, several bathrooms, intensive use). Also useful if you want to heat in off peak hours and use the rest of the day. | 5 or more |
Our tips for you to save with an electric water heater
It is important to remember that the water heater does not consume only when you shower, it also consumes due to thermal losses (maintaining hot water) and bad usage habits. Thus, you have to follow these tips:
- Adjust the temperature (do not set it to 75 ºC just in case). A usual efficient range is usually 50 to 55ºC. Higher temperature implies more losses and more consumption. Also, the higher the temperature, the more calcification.
- If you have time discrimination, program the heating in cheap hours. Heat the water in off peak and reduce heating in peak. If your water heater does not have a programmer, it can be solved with a timer or a programmable plug (provided the installation allows it).
- Do not oversize for convenience. A water heater that is too large gives you peace of mind, but also keeps more hot water for longer. Result: more losses and more expense.
- Check the insulation and location. A water heater in a cold gallery or an uninsulated room loses more heat. If it is in a warm indoor space, it will lose less.
- It must be given minimum maintenance. In areas with lime, the magnesium anode and the resistance suffer. A water heater with a lot of lime heats worse and consumes more. A periodic review can extend the useful life and lower consumption.
- Efficient shower heads. A good efficient showerhead reduces flow without it seeming like you are showering with a trickle of water. Less hot water used equals less kWh.
How long does a shower last with a 50 liter water heater?
A 50 liter water heater can give a shower of between 5 and 10 minutes under normal conditions. The range is 5 minutes because it will also depend on the temperature of the water heater, the temperature of the incoming cold water, the shower flow and what you prefer.
As a practical reference:
- If the shower is moderate and you do not exaggerate with temperature and flow, 10 minutes is a reasonable number.
- If in winter the water comes in very cold or the shower has a lot of flow, it can drop to 6 to 8 minutes.
- If the shower is efficient and warm, it can be stretched a little more.
To summarize, if your goal is to get the purchase right, stick with this idea: the optimal capacity for an electric water heater is the one that covers your daily routine without falling short, but without heating extra liters just in case.
