Coating & Tank material in water heaters (Stainless steel, Polymer, Glass Lined)

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What is the main purpose of buying a water heater?

You need hot water to bathe, wash utensils, etc during the winter months. The water heater enables you to do that.

When you venture into the market to make the purchase, you tend to get confused over which geyser to buy because of the wide range of appliances available on display.

You either end up buying the one your friends or relatives recommend or the one the salesman pushes you to buy. You make the wrong choice in both the cases.

This is because the requirements of each family are different. This water heater buying guide can solve many of your issues. In this part, we discuss the different types of coating and material of the storage tank and its effects.

Coating –Why?

The purpose of buying a storage water heater is that you are able to store hot water to use it subsequently when required. The storage time could be ten minutes or even an hour depending on the utility.

Under such circumstances, you cannot avoid corrosion. Secondly, you find the input water supply is always in the ‘ON’ position in geysers. Hence, these water heaters are always full of water every time.

This brings the corrosion aspect into the picture. The water heater manufacturers coat the inner surface of these appliances with an anti-corrosive material to prevent corrosion when it is in contact with warm water. This increases the longevity of the appliance.

Storage Tanks – Materials Used

These are the normal materials used in manufacturing storage tanks in geysers.

  • Copper
  • Stainless Steel
  • Thermoplastic

Let us do the comparison among the three materials mentioned above. Everyone knows that copper is a good conductor of heat.

This can result in heat loss. Stainless steel is a better option as it provides comparatively better insulation. Both stainless steel and copper are corrosive thereby requiring an anti-corrosive coating.

Thermoplastic is non-corrosive but is not a good insulator. This comparison brings us to the conclusion that stainless steel tanks are the best as far as the combination of insulation and anti-corrosive properties are concerned.

An additional layer of protection over the stainless steel tanks can serve the purpose. Let us go into the details of such anti-corrosive coating materials.

Coating Materials

As you narrow down your selection of water heaters, you come to the nature and quality of coating materials used in geysers. You will come across names as follows.

  • Porcelain Enamel Glass Lining
  • Glass Coating
  • Vitreous Enamel Coating
  • Blue Silicon Enamel Coating
  • Polymer Coating

The Significance

If you look at it carefully, the first four mentioned coatings constitute use of glass in some way. They are different kinds of processed glass coatings.

The process of coating metals with glass is a complex one. We need not go into the details. To get a basic understanding, glass powder is applied on the metal surface. When you heat it inside a furnace, you get a glass coating on the metal. This can provide protection against corrosion.

Glass is a bad conductor of heat. Hence, you get quality insulation when you use glass in combination with stainless steel.

Polymers are different in the sense that they are synthetic materials. You apply these polymers like paint on the metal surface to prevent corrosion. The question arises as to which one is better, glass coating or polymer coating?

As far as popular usage is concerned, glass coating have a wider acceptance. However, there are chances of damage to the coating on persistent use. The verdict is that polymer coatings are theoretically better than glass coating.

Final thoughts

Better the insulation lower is the heat loss. This factor along with the standing loss concept drives the BEE star ratings. Hence, the ideal combination should be a stainless steel tank with polymer or glass coating.

The star rating is an important factor. Go for a 5-star rated geyser. It might be a bit expensive initially, but the costs work in your favor when you use it for a long time.

The warranty offered by the manufacturer has a bearing on your decision. Normally, you have manufacturers providing a longer warranty on geysers having better corrosive protection. Checking out the warranty before purchasing the appliance is advisable.

Sources:, Wikipedia,, Kyodo

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