Installation costs for unvented cylinders can range from £550 to over £2000. If you already own one, you can be on the lower end of the range depending on the brand and kind you choose to replace it. A direct unvented cylinder replacement part could start from around £500. Suppose you don't have an unvented cylinder but are considering installing one. In that case, you'll probably need to increase the cold water main's capacity from the incoming stop tap to the unvented hot water cylinder. First, it will be necessary to evaluate the dynamic pressure test, water pressure, and water flow rates. It will bring about more considerable expenses.