One of the most common question, related to water heaters, that is asked by readers of Bijli Bachao is: “Should I buy an instant water heater for my bathroom?”. We have frequently received this question since the time we published an article stating that Instant Water heater is the best to save electricity. We have always replied to people that: one should use instant water heater only for small uses like for wash basins and kitchen, however in this article we will provide the detailed analysis of why it does not make sense to buy instant water heater for bathing.
What is Instant Water Heater?
First let’s get the definition right. Instant water heaters are those that have small storage capacity (3 lts or 1 ltr) and high heating rate (3 kW or 4.5 kW). Water heaters having storage capacity more than 3 lts are categorised as storage water heaters. The reason they are called “instant” is because due to low storage volume and high heating rate it can provide hot water “almost” instantly. But how fast is this instant as compared to your requirement? Let’s check it out.
How much time does Instant Water Heater take to heat the water
We did an analysis of minimum winter temperatures across the country and saw that the temperature of water in winter can be between 4oC and 21oC (it cannot be lower than 4oC as it will become Ice) depending on the city where you live.
Taking this into consideration we did some calculations to find out how much time an instant water heater will take to heat the water to high temperature (of about 60oC) and useful water temperature (of about 39-40oC which can be used without mixing cold water). As per our calculations an instant water heater would take about 1 minute on an average to heat water to useful temperature and 2 minutes to heat to high temperature.
The best case scenario is when a 1 ltr water heater with 4.5 kW heating element is used in a city where peak winter temperature is 21oC. And even in that case time taken to heat to useful water temperature is 20 seconds.
Flow rate of water from taps and shower
Typical taps have a flow rate of 3 lts/min and showers have a flow rate of 8 lts/min on an average. These numbers may vary with tap or shower type and even with water pressure. High end taps/showers (like rain shower, etc) may consume lot more.
Are instant water heaters really useful for bathing?
If we take lowest flow rate of 3 lts/min then the only scenario (of instant water heater) which can work is when you are in a city where peak winter temperature is 21oC and you have a 1 ltr water heater with 4.5 kW heating element. Only then will you get continuous hot water at useful temperature. And this is the only scenario when instant water heater can work. In all other cases it cannot.
So to really answer the question: “Are instant water heaters really useful for bathing?”, the only response that we have is: “No, Instant water heaters are not very useful for bathing.”, and this answer is good in most cases, unless you are fine with waiting for a few seconds for the water to heat up again. Which may be possible if you are taking a bucket bath, but if you are planning for a shower bath, be ready to be disappointed if you use instant water heater.
When can you use instant water heater?
Instant water heaters are good for places where it is needed just for hand wash or small water use. It can work great if you plan to use it in your kitchen. Anywhere else where the usage of water is more, you should go for a bigger storage water heater (6 lts or above).
Is 6 lts water heater instant?
Many people confuse 6 lts water heater as instant water heater. It is not classified as instant water heater. And the reason for that is that time taken to heat water increases as the size of water heater increases, and thus they are not classified as instant water heaters.
Are Gas Water Heaters instant?
Gas water heaters are better than electric instant water heaters as they have much faster heating capacity. And yes they certainly are instant.
If you really want instant water heater for your bathroom, then the best option that you have is to go for gas water heaters. Electric instant water heaters will not work in most cities in India.
Some Good Instant Water Heaters:
About the Author:
Abhishek Jain is an Alumnus of IIT Bombay with almost 10 years of experience in corporate before starting Bijli Bachao in 2012. His passion for solving problems moved him towards Energy Sector and he is keen to learn about customer behavior towards Energy and find ways to influence the same towards Sustainability. More from this author.