You may have previously wondered how a boiler can feed an entire office building, or how large premises such as hospitals and care homes are heated. In some cases, a large commercial boiler may be used, however, in other cases, multiple boilers may be connected together using something known as a low loss header. 

Below, we’ve identified what a low loss header is as well as how it works and when you might need one. 

What does a low loss header do?

A low loss header is installed to ensure that the flow rate of water is high enough to be able to heat a large building or even multiple buildings, such as an office complex.

The header does this by increasing the flow of water that passes through the secondary heating circuit adding to the water from the primary boiler circuit.

A standard boiler will have a minimum and maximum flow rate that is determined by the manufacturer. However, because of the way in which it is directly connected to the heating system, it will have a variable flow rate. This is usually dictated by various control valves. Where there are multiple boilers in one system, a low loss header can regulate their flow rates, making the whole system more economical. This could result in a higher-performing, more efficient boiler with a consistent water temperature that can reach your radiators.

However, a low loss header cannot work efficiently if there isn’t a suitably sized pump that is also installed in the system. If the pump is too small, the hot water that is created by the appliances won’t be able to reach the radiators that are furthest from the boilers. If the pump is too big, it might be pushing hot water around the radiators too quickly, therefore wasting energy. Two pumps will be required in effect, one from the boiler to the low loss header and one from the low loss header to the heating system. 

Why use a low loss header?

You would likely need a low loss header if you have a very large home or business premises and you’re using a low water content boiler. Your low loss header will need to be sized correctly depending on the flow rate of water around the building.

A low loss header is also a good device for removing debris and sludge from your heating system. Over the years, dirt can enter your system from the mains supply or from the water that is stored in the cold feed tank. In addition to this, the pipes in your system can begin to corrode, causing a build up of dirt. If this builds up too much, it can stop your radiators from heating up fully. If your radiators are cold at the bottom, you may have a build up of sludge.

A low loss header usually has a drain at the bottom of it. Hot water passes through the header at a lower pressure than it would pass through the rest of the system. This reduction in pressure and speed allows time for any dirt and debris in the system to sink to the bottom of the header. The drain in the header can then be opened regularly to release any dirt and completely remove from the low loss header. This will allow your system to remain efficient over time. 

How does a low loss header work?

Within a boiler system, there is a primary circuit and a secondary circuit. The primary circuit is responsible for the actual heating of the water, so a boiler and a pump is included in the primary circuit. The secondary circuit contains any of the items that transfer heat or energy, so in the case of a heating system this could be the radiators or underfloor heating. A low loss header is able to combine these two The primary water flows into the low loss header to provide the heated water which is added to the water in the secondary circuit providing the correct flow rate around the heating system.

A low loss header will be used alongside the rest of the heating system, therefore other factors need to be considered. If there is no pump in the heating system, one will need to be added. You also need to consider the minimum and maximum flow rates of the primary circuit, as well as the systems that are installed on the secondary circuits, for example, underfloor heating. 

How to size a low loss header

You should size the low loss header based on the maximum system flow rate of your system. A suitably qualified heating engineer will be able to advise on which size you may need based on a number of factors.

Representative Flow Rate Calculation for Low Loss Header

Load kW / (Specific heat capacity of water 4.18 x temperature differential of heating system)
Equals litres per second x 3600 to give cubic metres per hour

Low loss headers are sized in cubic metres per hour. A low loss header cannot be oversized, but can be undersized.

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