Direct hot water system ? What are they ? 

A direct-fired hot water system is powered by a direct-fired water heater, whereby the water’s heat source is physically contained within the hot water cylinder itself.

As such, a direct fired hot water heater has a built-in gas or oil burner or electric immersion heater elements that directly heats the domestic hot water.

Thus, the water in a direct hot water heating system is heated by heat sources physically located within the hot water cylinder or calorifier as opposed to an indirect hot water cylinder, which generally speaking use a water supply from another heat source to heat the water via an internal coil.

Direct domestic hot water heating systems to heat water

Advantages of direct hot water systems

Direct fired water heaters are devoted to the production of domestic hot water only, allowing for a quicker heat-up and response time than indirect hot water cylinders or systems, which essentially use “heating water” from a central heating system via an indirect hot water cylinder for the purpose of heating sanitary-grade hot water and are by definition less efficient.

Advantages of separating the hot water and heating systems

Direct hot water heaters are frequently placed close to the point of use, which minimises distribution heat losses and lowers the energy needed to supply water over a long pipe run. Additionally, by doing this, the system’s dead legs and portions of inactive or infrequently used pipes that represent a Legionella danger are reduced in length.

The Health and Safety Executive L8: Approved Code of Practise and Guidance for the Control of Legionella Bacteria in Water Systems, which specifies that the distribution pipework should be adequately designed to enable the water to reach all outlets at 50°C within one minute of turning on the taps, supports compliance with regulations such as this.

Gas fired direct hot water heaters

Direct gas fired hot water systems consist of an integrated gas burner that can be powered by natural gas or LPG (propane) gas that heats the water in the storage vessel directly to produce domestic hot water, controlled by a thermostat in the water heater.

They function by delivering heated gases through the heat exchanger, which is normally an internal coil or may be fire tubes located within the hot water cylinder to heat water. The heat from the heat exchanger is then transferred to the cold water surrounding it, thus heating the water to the desired temperature in an energy-efficient manner.

Indirect hot water systems

A dedicated central heating hot water boiler and an indirect hot water cylinder would be installed in an indirect hot water system. The same boiler is now capable of serving both the heating circuit and the domestic hot water system. When no space heating is required, the boiler must continue functioning to produce heat for the domestic hot water system.

Generally, indirect cylinders also come with an immersion heater or immersion heaters as an emergency backup, heating the water directly in the cylinder in the event of a fault with the heating boiler.

What is a direct hot water cylinder?

A direct hot water cylinder: A direct hot water cylinder heats the water using heat sources that are directly located within the cylinder, such as an electric immersion heater. These hot water heating systems are typically found in buildings that do not have access to gas or would prefer to use electricity as the primary energy source for environmental reasons such as low or zero carbon emissions.

Direct cylinders are available for domestic applications. We go into more depth here –

Direct hot water cylinder range from 80 to 500 Litres

or our commercial and industrial direct hot water cylinder range, which can be fitted with large immersion heating elements and store hot water up to 5,000 litres in volume. More on this range here –

Commercial and industrial direct cylinder / tank range

Storage Direct and Indirect Hot Water Cylinders

Direct or indirect heating of your hot water cylinder depends on your requirements and site conditions; either way, Flexiheat UK has a solution for you, as we have both an indirect hot water cylinder range and a direct hot water cylinder range to suit all your calorifiers requirements.

Contact our sales team at 01202 822221 or use our email contact form for further assistance.