What are the disadvantages of a direct cylinder?
The main disadvantage of a direct cylinder is running costs. Electricity is generally pricier per unit than gas, so heating a full cylinder with immersion heaters can be more expensive than a gas boiler or other source of heat. This is especially important in larger homes, commercial properties or buildings requiring large amounts of hot water.
However, most users of direct cylinders heat up the hot water cylinder when cheap-rate electric tariffs are available, normally at night, so when they wake up in the morning, they have a full tank of domestic hot water that has been heated at the most economical price to see them through their daily DHW needs.
Our most common direct cylinders are detailed on this webpage – https://www.flexiheatuk.com/product/unvented-direct-cylinder-80-litres-to-500-litres-stainless-steel/
Another disadvantage is the heat-up time. A powerful boiler connected to an indirect cylinder might heat a full cylinder quicker than immersion heaters. You’re using a lot of hot water quickly, and the cylinder may need time to recover before you can get more hot water.
A direct cylinder also relies completely on electricity. If the power is cut or there is an electrical fault, the water in the cylinder will not be able to be heated. The electrical supply must also be suitable, as immersion heaters are high-load appliances and require the correct wiring, controls, protection and isolation.
Furthermore, the incoming mains water pressure and flow rate must be suitable for direct unvented cylinders. Poor mains supply? Hot water performance at taps and showers can be disappointing. They, as with all unvented systems, need to be fitted with the correct safety controls and discharge pipework and be serviced regularly by a competent person.
The main disadvantages of a direct cylinder can be higher running costs, reliance on electricity, slower recovery times and the need for a suitable electrical and mains water supply. However, in the right application, they can still be a practical and reliable hot water option.
