Choosing the right size cylinder is essential to cater for the hot water demands of your home. The right size hot water cylinder is crucial because it needs to be large enough to handle the demands of hot water usage in your home. Too big a cylinder will store more water than you need and also waste energy in the heating process. Too small a cylinder will leave you lacking available hot water. Some people may worry that having a hot water storage cylinder means that you’ll run out of water whilst having to wait for it to fill up again, but if you select the right size for your property this shouldn’t happen. The capacity of a cylinder will change depending on whether it’s being heated by an indirect heat source such as a boiler or directly for example by an electric immersion heater. The cylinder capacity is always measured in litres, which may not be entirely useful when thinking in terms of daily showers, baths or washing up. Both vented and unvented hot water cylinders are available in a wide range of sizes and can vary anywhere between 74 litres (16 gallons) to 450 litres (99 gallons). The easiest way to work out what size and capacity you’ll need is by looking at the number of household occupants, bedrooms, bathrooms and showers you have. When deciding what size hot water cylinder you’ll need there is a general rule you can follow… Allow around 35-45 litres for every household occupant. It’s crucial to consider the combination of your cylinder’s capacity and re-heat times, especially during the periods of highest demand and also future-proofing your cylinder. On average, a standard domestic household with 4 occupants will use around 200 litres of water a day. However, it should be noted that hot water cylinder sizes will differ depending on the household and your own usage.