Hot Water Heater: Storage Water Heater vs Tankless Water Heater

Hot water is required in house for various purposes like cooking, bathing, cleaning, etc. Water Heaters are installed/fitted for heating water and are connected to various appliances. Fuels commonly used in water heaters are electricity, gas, oil and solid fuel i.e wood and biomass and even solar energy is used.

Water heaters are of two types: Storage Tank Water Heater and Tankless Water Heater irrespective of fuel used for heating.

Courtesy - Mr. Plumber Atlanta
Courtesy - rvupgradestore

Storage Water Heater

 Instantaneous  Heater/Tankless Water Heater

  • In Storage Water Heater water is first filled  in the tank and then heated. It needs time to heat the water i.e hot water is not instantly available. One has to switch on before you want to use, if it is an electric heater.
  • In Tankless Water Heater incoming cold water enters through inlet, passes through heat exchanger in which it gets heated and hot water is instantly available at outlet. One don’t have to wait.
  • It consists of thermally insulated vessel (tank), thermostats (temperature sensitive device), pipes and heating elements (either electric heating or gas burners).
  • It consists of switch, small pressure vessel with heat exchanger and a pilot lamp (a lamp that lights up when circuit is closed). The heater is to be switched off immediately after use, hence no thermostat is required.
  • When water is heated, thermostat will sense water temperature and automatically stop further heating.
  • Switch has to be turned off to stop the heating of incoming water.
  • Only the amount of water in the tank is heated i.e quantity of water available would depend on capacity of heater.
  • All the water coming is heated on time continuously.
  • Once the hot water is used tank gets refilled and water is heated again in tank, which will need time.
  • Once the water is used, incoming water is heated and hot water is available continuously.
  • Continuous hot water flow is not available.
  • Continuous hot water flow is available.
  • Hot water stored in the tank constantly looses heat.
  • Do not generate standby energy (heat) losses.
  • CO2 emissions are more.
  • CO2 emissions are less.
  • Life span is 10 to 12 years.
  • Life span is about 20 years.
  • These heaters affect the quality of water due to storage of water in tanks.
  • Water quality is not affected because water is not stored.
  • Hot water flow is available as soon as hot water tap is turned on, of course allowing initial heating time which maybe 10 to 20 minutes depending upon its capacity.
  • Exchanger first builds up the temperature and then hot water comes and hence may take few minutes or more.
  • If temperature of hot water reduces below 60° C water stored in tank gets contaminated due to breeding of bacteria.
  • No water contamination as no water is stored in heater.
  • Suitable for large establishments.
  • Suitable for small establishments.
  • More pipe line causes heat loss during conveyance of hot water from storage water heater to the fixture.
  • Less heat loss due to short pipe length for conveyance of hot water.
  • The flow (quantity of water coming from tap) and velocity (the speed at which water comes) is good. Hence, better for use; provided capacity is adequate.
  • The flow and velocity both are comparatively less than storage water heater and hence not very comfortable where more water is required.
  • More advisable and suitable when used with combined taps (hot and cold water) i.e with mixer body, diverter, etc.
  • Not suitable as less water flow.
  • It can be common for more than one bathroom of a house, reducing capital cost.
  • It can be common for more than one bathroom of a house, reducing capital cost.
  • Capital cost i.e initial cost is more.
  • Capital cost is less but uses more power in case of electric gyeser. Gas gyesers are cheaper than electric.
  • More suitable for shower, bathtubs, etc.
  • Less suitable for shower, bathtubs, etc.
  • Needs more space due to tank.
  • Acquires less space, except electric.

Fuels for Water Heaters

  • Electricity – Electrical Storage Water heaters.
  • Gas – Gas water heater.
  • Solid Fuel (wood, coal, biomass, charcoal) – Boilers
  • Solar Water Heater
  • Electricity – Geysers (Instantaneous Water Heaters)
  • Gas – Gas Geysers
  • Electricity – Geysers (Instantaneous Water Heaters)

Buying Guide

  • These heaters are sold as per the capacity i.e minimum amount (gallons/liters) of water a geyser can deliver. Eg: A 30 gallon storage heater will store and yield 30 gallons (114 L) of water. One may choose based on family size. Make choice of heater accordingly.

Minimum Gallon(G)/liter(L) Capacity

Family Size Electric Gas
For Cold Countries
1-2 30 114 30 114
2-3 40 151 40 151
3-4 50 189 40 151
5+ 80 303 50 189
For Tropical Countries
1-2 4 15 4 15
2-3 7 25 7 25
3-4 9 35 9 35
5+ 13 50 13 50

First Hour Rating (FHR) is taken into consideration. It is the number of gallons of hot water the heater can supply per hour(starting with a tank full of hot water). More FHR means more quantity of hot water available.

  • Always choose more efficient (more stars) water heater.
  • These heaters are sold on the basis of quantity of water required at fixtures. Normally this is the water quantity required.


Avg Flow GPM 


Tub 4.0 18
Shower 2.5-3.0 11-13.5
Washing Machine 2.0 9
Dishwasher 1.5 6.8
Kitchen Sink 1.5 6.8

Add the GPM of fixtures in use and make choice of heater accordingly. For Ex: If a user has shower, washing machine and sink. He should prefer (3.0+2.0+1.5) 6.5GPM water heater.

  • Gallons per Minute rating (GPM) i.e quantity of water flow available per minute is taken into consideration. Ex: A 6.5 GPM water heater will deliver 6.5 gallons (25L or 1 bucket) water in 1 minute.
  • Always choose more efficient (more stars) water heater.

Bottom line: Tankless water heater saves energy as well as quality of water is maintained where as if economy is priority and more hot water is required than one should opt for storage water heater.

Also Read:          

Domestic Water Supply System
Direct Water Supply System vs Indirect Water Supply System

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