Why boiler flow rates matter

Upgrading a homes central heating system is not just about deciding on the power output of the boiler required or the efficiency levels that are stated.  It also requires knowing what water flow rate you currently have.

More often than not, water flow rates are left to last because the specs of the boiler are to most, more appealing.  However if you have a boiler fitted that has a flow rate higher than what your home can supply, your boiler will never work at its stated capability and your home will be heated inefficiently.

The amount of water that is able to flow through your combi boiler is restricted by the volume of water that can be supplied by the water mains themself.  This means that if you have a boiler with an optimum flow rate of 15 litres per minute (combi boilers need at least 10 litres per minute flow rate to operate) but the mains supply flow rate is only 11 litres per minute, it means that the mains water supply to the boiler is simply not enough to maximise the output of your combi boiler.

If a 24kW combi boiler can deliver 10 litres of hot water per minute at a temperature lift of 35oC while a 40kW combi boiler can deliver 16.5 litres of hot water at a temperature lift of 35oC; if the mains water supply can only supply 12 litres of water per minute then the 40kW boiler is simply not able to work properly.

A combi boiler requires good incoming water pressure and a good internal flow rate in order to operate correctly.  Because of the history of existing infrastructure in Scotland, England and Northern Ireland, mains water pressure is frequently reducing in most areas and new homes are built that tap into existing pipelines.  As a result of this, more and more homes begin to suffer from low water flow rates. And this can have a big impact on what type of combi boiler you can have fitted.

To overcome this, you can have a pump installed into your water mains supply to help boost the pressure but push pumps are designed to push water, not pull it so you still need to ensure that you have a sufficient supply of water from the mains.  Push Pumps are limited to 12 litres per minute to ensure that they do not damage the existing infrastructure and you can install a break tank with a push/pull pump fitted to increase your flow rate but this is a big investment.  Your standard 3 bedroom home would require a 200 litre break tank!

How Flow Rate Works with Heating Water

The hot water flow rate  is calculated as litres per minute (LPM).  This indicates the speed at which your combi boiler can heat water that is supplied to the taps of your bath, shower, sink etc.  Because of the different mains water pressure and varying boilers on the market, your hot water flow rates on combi boilers is anywhere from 9.8 LPM to 25LPM.  As a boiler installer, it is part of our job to calculate your hot water requirements using how many bathrooms you have and how often you need to use them at the same time.

For example, a single bathroom property only requires a small combi boiler installed with a flow rate of around 10 LPM.  In bigger properties with two or three bedrooms, you need to have a higher hot water flow rate to cope with demand should the shower be used at the same time as the hot tap in the kitchen sink. With more than 100 different models of combi boiler currently on the market, it is easy to see how so many home owners can get lost in choosing what boiler they need.  Quality, Efficiency, Price and Warranty Length are all normally the main deciding points but understanding the water flow rate of your property is a vital part of knowing what boiler you CAN have fitted.

HF Heating Services

From industrial heating to plumbing systems, air conditioning installation and servicing to domestic plumbing/heating issues, we specialise in all commercial, retail and domestic plumbing, heating and air conditioning services.

Our domestic plumbing services means that we can offer our customers everything from bathroom fitting to kitchen fitting services and annual Gas Safety checks.

With over three centuries of experience, the HF Group continues to grow and evolve; to improve our level of service and the quality of our work.  From initial enquiry through to project completion, we appoint a manager who oversees the entire project and ensures every client need is met, every step of the way. In a world where customer service increasingly means call centres and multiple management, we believe ours is a refreshingly different approach.

We are an ambitious and diverse family of companies offering superior quality and exceptional customer service.   Attracting and retaining the best talent creates positive returns and ensures we continue to make a significant contribution for our customers, staff, suppliers and communities.

HF’s family culture stretches back over three centuries in business yet it means much more than dates and numbers. It’s quite literally, the core of our business.  With senior-level hands-on management from initial planning to final handover coupled with the opportunity to tap into a wide range of varied services and associated consultants, we can offer our customers unsurpassed levels of genuinely in-house capabilities. All driven by the values that are instilled in our entire team across all the companies within HF as ‘A Company Well Connected’.