Understanding Combi Boiler Flow Rates
In general, the more bathrooms and showers you have, the greater the flow rate you’ll need. Our heating engineers talk you through combi boiler flow rates and what they mean.
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Most combi boilers are suited to homes with one or two bathrooms and they can usually meet these hot water demands.
However, if your combi boiler has low mains water pressure, your combi boiler may not be able to deliver the high flow rates you’re looking for.
Key Points:
- A good flow rate on a combi boiler should be between 12-15 litres per minute
- Having a boiler flow rate higher than your mains supply flow rate can result in wasted money
- Installing a pump into your mains supply can help to increase your boilers flow rate
What is boiler flow rate?
Boiler flow rate is the volume of hot water that passes through a boiler every minute and it is usually measured in litres per minute (L/min). In general, the more bathrooms and showers you have, the greater the flow rate you’ll need.
However, it isn’t that simple. The amount of water that can flow through your boiler is dictated by the volume of water supplied from your mains, also known as the mains supply flow rate. So when you install a new boiler, you need to ensure it has a flow rate that matches the mains supply flow rate.
What should the flow rate be on a combi boiler?
The ideal flow rate for a combi boiler should be between 12 to 15 L/min. Anything below 10 L/min is considered a low flow rate and will not provide sufficient water pressure in your home.
Choosing a combi boiler with a good flow rate will help you to optimise hot water pressure in your home. However, it is important not to choose a boiler with a higher flow rate than the mains flow rate, as you will be wasting money since the boiler won’t reach its full potential.
How important is the flow rate on a combi boiler?
Understanding the flow rate of your boiler is essential for helping you understand the speed in which hot water can be provided to your taps and showers.
The more taps and showers you have in your home, the higher the combi boiler flow rate you’ll need, especially if they are frequently used at the same time. For properties with two or more bathrooms, it is essential to opt for a boiler with a higher flow rate since it will be halved, for example, if two showers are in use at the same time.
Can you save money with lower or higher boiler flow rates?
When your combi boiler is installed, the flow temperature is usually set to around 70-80°C. This is normally too high for most combi boilers to run at maximum efficiency.
Lower flow rate temperatures result in a more efficient combi boiler since it uses less gas to heat your home to the same temperature, therefore saving you money.
How to measure your boiler flow rate
Measuring your boiler flow rate is super simple and you will only need two pieces of equipment: a stopwatch (a mobile phone will be sufficient) and a measuring jug.
Start by placing the jug under the cold tap in your bathroom and turn it on, allowing the water to run for exactly six seconds. Now take the volume of water in the jug in litres and multiply it by 10. For example, 0.10 litres x 10 = 10 litres per minute.
Anything below 10 litres is usually considered low pressure and so you should ideally be looking for a reading between 10-15 L/min.
If you are planning on changing your boiler, you should establish your mains flow rate and then find a combi boiler with a compatible flow rate.
Can you increase your boiler flow rate?
Yes, you can increase your boiler’s flow rate and one of the easiest ways to do so is by installing a pump into your mains supply. This will help to boost the water pressure coming in from the mains, however, you will still need to ensure you have an adequate supply of water since the pumps are only designed to push water.
There are also specific laws in place that limit pumps to 12 L/min to protect the mains infrastructure. However, this may not be enough for some homes considering some showers use as much as 9-15 L/min.
For homes that need a flow rate higher than 12 L/min, a break tank can be installed to provide a reservoir of water. The pump can then be installed to supply water at a higher flow rate.
If you don’t think your boiler has a high enough flow rate for your home and you’d like to have a pump installed, contact our team today to find out how we can help you increase your boiler’s flow rate.
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