FlexEJ Low Loss Header Calculator
Check your low loss header calculations and find the LLH you need.
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Full in-house design & manufacture to EN / ASME / PED.
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Low Loss Header Calculator
The FlexEJ low loss header calculator will allow you to size a low loss header based on the flow or power in your primary and/or secondary circuits. If you have any questions or require guidance on using this calculator please contact us.
The FlexEJ LLH Calculator Alert
Please rotate your screen. Our LLH calculator requires just a little more horizontal space than we can squeeze into your current rotation.
Design Values
Primary dTPrimary Circuits
Secondary Circuits
Calculation Result
calculator notes
Low Loss Headers can either have multiple connections to the body – 1 pair per circuit – or these can be combined before/after the LLH in horizontal headers (our preference) which results in just one pair of primary connections and one pair of secondary connections.
The calculator covers both connection schemes by providing 4 separate primary and secondary inputs plus a total which represents the horizontal header implementation.
Fixed standard values for the properties of water are assumed when converting from power to flow rate.
Standard Products and Enquiry Form
As you use the calculator, you will see below any available FlexEJ standard low loss headers that match your application and an enquiry contact form.
FlexEJ standard low loss headers are designed for use with horizontal headers.
We offer short lead times on manufacture of bespoke low loss headers for use without horizontal headers – individual circuit connections to the body – and larger sizes above the standard range.
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Frequently Asked Questions
A. Yes, to some extent, as the flow velocity in the body is low. We provide a Flamco AAV and DN25 drain valve on all FlexEJ low loss headers. However, separation is not as efficient as using a dedicated air/dirt separator as the main low velocity section in the LLH is bounded by turbulent cross flows.
A. Opinions vary but ideally all the primary circuit and secondary circuit flow and returns should be brought together in horizontal manifolds before connection to the low loss header.
A. On a vertical low loss header the returns connect at the bottom and the flows at the top. If the connections are staggered side to side then the lower pair are normally the primary side.
A. Sizing can be expressed in terms of flow rate or power. In heating systems, the total boiler power in the primary circuit is often taken as the sizing criteria. The power rating is directly proportional to the flow rate and temperature difference as given by m.Cp.Δt – Power (kW) = Mass flow rate (kg/s) * Specific Heat of Water (kJ/kg°K) * Temperature difference (°K). Our product table above shows both nominal flow rate and power ratings.
A. We have an online low loss header calculator we’ve built to help you – or do please get in touch with the details of your system and we will be pleased to help.
A. Based on the flow rate through the low loss header the body is sized to achieve a very low flow velocity – typically less than 0.3m/s. This low velocity ensures a low pressure drop between flow and return.
A. Yes – strictly speaking hydraulic separation between circuits is achieved using a low loss header.
A. A low loss header (LLH) provides hydraulic separation between multiple pumped circuits. This allows each circuit to operate independently and to be controlled for optimum efficiency. The header presents very low pressure drop bypass between the flow and return. FlexEJ low loss headers are provided with sensor ports on all four branches so whatever control system is being implemented you will have the port you need.
