How the instant hot shower saves electricity bills

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

18 June 2006

George Kimani is considering installing an instant hot shower system in his house. But he has noted that many of the products available in the market are rated at between 3,000 and 6,000 watts. He says, “This is very high compared to the 1,500W of the regular water heater.” His question is; “can the new system help reduce my power bill?”

Kimani is correct regarding the power ratings of the two types of heaters, but their greatest difference is in the way they are used. The average water heater has a 75- to 100-litre tank and a 1.5-kW (1,500 watts) heating coil. If it is switched on for one hour, it will heat enough water for about two showers – a third person will probably rinse with cold water.

Now, electricity is sold in kilo-watt-hours (kWh). One kWh is the amount of energy consumed when a one-kW (1,000-watt) appliance is left on for one hour. Therefore, running the ordinary water heater for one hour will consume 1.5kWh.

But since this gives enough water for two and a half showers, it means that each shower consumes about 0.6kWh (1.5 divided by 2.5). In one month (30 days), the total consumption comes to 18kWh per shower.

The advantage of the instant hot shower is that there is no reservoir tank. Its heating coil only comes on when the water is turned on. Thus the heater is on for a very short time during a shower.

Consider the showering process: You turn on the water and wet your body for about one minute. Then you turn it off and apply soap on yourself. Finally you turn the tap on again to rinse and probably sing a song as you enjoy the warm water running down your skin. This final cycle can be about two minutes.

In total, therefore, the average shower requires about three minutes of continuously running water. In one month, this accumulates to 90 minutes or one and half hours. That is, the instant heater will also be on for 1.5h per month per shower. At a power rating of 4kW, the total energy consumption comes to about 6kWh. This is, one-third the consumption of the regular water heater (18kWh).

But the greatest saving of the instant hot shower is realised if you live alone. This is because when you use the normal heater, you still have to keep it on for about 45 minutes before the water is warm enough for a shower. The energy consumption in this case comes to about 34kWh (1.5kW times 0.75 hours times 30 days).

It turns out therefore that you can save at least 30kWh when you fit the instant hot shower. This translates to about Sh 300 per month. Since these units cost about Sh 2,000, the savings will pay back in about six months. It is no wonder then, that so many people have gone the instant shower way.