When choosing the right combi boiler for you, one of the key considerations comes down to the water flow rate. A good installer will ask or check this for you before recommending a boiler.
How is water flow rate measured?
It is measured in litres per minute (l/min) and this is an important factor when choosing the right combi boiler. The higher the number the more hot water you get through your tap. It is measured with a weir cup by plumbers and heating engineers.
Here’s a list of the best combi boilers that have high water flow rates:
- Alpha E-Tec Plus 38W
- Baxi 600 36kW
- Ideal Logic C35
- Viessmann Vitodens 111-W
- Worcester Bosch 8000 Style 35kW
What is a good water flow rate for a combi boiler?
With combi boilers, you are always limited in how much hot water you will get per minute. But for a hot bath to fill quickly or a good shower, 14 to 16 litres per minute is considered a good rate. To make it higher, you will likely need a storage combi or a conventional boiler with a separate storage tank.
Water flow rate is the amount of water that comes out of your taps, measured in litres per minute, the more water comes out, the higher the flow rate. It is dependent on pipework, valves and taps in the plumbing system installed in your house. Factors such as water pressure (the force of the water) can also impact the flow rate.
Flow rate is different from the water pressure in that the force at which the water comes out is called the pressure rather than the amount that comes out.
How to measure flow rate in your tap
Turn the cold tap nearest to where your boiler is or will be on full, and use a 1 litre measuring jug and a stopwatch. Press start on the stopwatch as soon as you put the jug under the running tap, and stop the timer when 1 litre is filled.
Use the following chart to easily find what the flow rate is from your tap.
Water Flow Rate Chart
| Time to fill 1 litre jug (in seconds) | Litres per minute |
|---|---|
| 2 | 30 |
| 3 | 20 |
| 4 | 15 |
| 5 | 12 |
| 6 | 10 |
| 7 | 8.5 |
| 8 | 7.5 |
| 9 | 6.7 |
| 10 | 6 |
| 11 | 5.4 |
| 12 | 5 |
| 13 | 4.6 |
| 14 | 4.3 |
| 15 | 4 |
What is the minimum flow rate for a combi boiler?
The minimum flow rate for a combi boiler is the lowest amount of water required to keep the boiler working efficiently. This is a crucial factor in ensuring that the boiler does not overheat and cause damage to the system.
The minimum flow rate varies depending on the make and model of the combi boiler, as well as the size of the property it is installed in. Generally, the minimum flow rate for a combi boiler ranges from 9-12 litres per minute (LPM). It is important to ensure that the flow rate is sufficient for the boiler to operate correctly, as a flow rate that is too low can cause the boiler to shut down and potentially break down.
If you are unsure about the minimum flow rate for your combi boiler, it is recommended to consult the manufacturer’s manual or contact a qualified heating engineer for advice.
Combi boiler flow rate to save money
According to various studies, including one by the Heating and Hotwater Industry Council (HHIC), lowering the flow temperature on your combi boiler can lead to significant savings. By reducing the operating temperature for heating, your boiler can run more efficiently without reducing your comfort.
Their research suggests that households could save about 9% on their total gas bill by doing this, assuming their flow temperature is currently set at 80°C. Nearly all combi boilers are not optimized to run as efficiently as they should, which increases household gas bills and emits more carbon.
By making a little change to your combi boiler, you can reduce your gas usage by up to 9% to save money while keeping your home just as warm.
When do you need a high water flow rate combi boiler?
Having a good performing boiler helps to fill a hot bath quicker and gives better shower output.
Combi boilers can struggle when there is more than one hot water tap open. But as they save space and are efficient, they will continue to be popular. If you have two or more bathrooms, or one bathroom and two showers and more than a couple of occupants, you will likely need a high flow rate boiler.
The alternative to having a more powerful combi is a system boiler. They are better for homes with two or more bathrooms because they store hot water in a cylinder. When the cylinder is full, two baths or showers can be run at the same time. Most combi boilers will struggle to do this.
Do you need a powerful boiler for higher water flow rates?
A higher water flow rate usually requires a high kW output boiler. A lower output combi of 24kW provides up to 10 litres of hot water per minute. When looking for a boiler that can supply more than one hot tap at the same time comfortably, you will need a boiler between 34kW and 42kW.
Now we have looked at some factors that go into choosing a good boiler that has a high water flow rate, let’s look at some of the best, in our opinion, combis on the market:
Viessmann Vitodens 111-W 35kW
The Viessmann Vitodens 111-W 35kW boiler is a high-performance wall-mounted gas condensing boiler known for its efficiency and advanced features. It is designed to provide reliable heating and hot water solutions for residential properties.
Pros:
- High Efficiency: The Viessmann Vitodens 111-W boasts a high energy efficiency rating, helping homeowners reduce energy consumption and lower utility costs.
- Large Hot Water Output: With a 35kW heating output and generous hot water flow rate, it is suitable for larger homes with higher hot water demands.
- Smart Technology: The boiler is equipped with advanced smart technology, including weather compensation and modulating controls, ensuring optimal comfort and energy savings.
Cons:
- Higher Initial Cost: The Viessmann Vitodens 111-W 35kW boiler tends to come with a higher upfront cost compared to some other models, which may be a consideration for budget-conscious buyers.
- Installation Complexity: Due to its advanced features and capabilities, professional installation is recommended to ensure proper setup and operation.
- Limited Availability: The Viessmann Vitodens 111-W 35kW boiler may have limited availability in certain regions or markets, which can impact accessibility for potential buyers.
Product Overview: The Viessmann Vitodens 111-W 35kW boiler combines reliability, efficiency, and smart technology to deliver excellent performance.
It offers ample heating power and a high hot water flow rate, making it suitable for larger households with increased demands. The advanced controls and weather compensation feature ensure optimal energy usage and comfort.
While it may come with a higher initial cost and require professional installation, the Viessmann Vitodens 111-W 35kW boiler is a dependable choice for those seeking efficient and reliable heating and hot water solutions
Alpha E-Tec Plus 38kW Combi
The Alpha E-Tec Plus 38kW Combi boiler is a powerful and efficient heating solution designed to provide reliable heating and hot water for residential properties. With its high output and advanced features, it offers enhanced comfort and energy efficiency.
Pros:
- High Heating Output: The Alpha E-Tec Plus 38kW Combi boiler delivers a high heating output, making it suitable for larger homes or properties with higher heating demands.
- Energy Efficient: It boasts excellent energy efficiency ratings, helping homeowners reduce energy consumption and lower their utility bills.
- User-Friendly Controls: The boiler features intuitive controls, making it easy to operate and adjust settings to meet individual comfort preferences.
Cons:
- Physical Size: Due to its higher output, the Alpha E-Tec Plus 38kW Combi boiler may have a larger physical size, which could require more installation space compared to lower-output models.
- Higher Initial Cost: The increased heating output and advanced features of the Alpha E-Tec Plus 38kW Combi boiler may result in a higher upfront cost compared to some other models.
- Limited Warranty: The warranty provided for the Alpha E-Tec Plus 38kW Combi boiler may be shorter or more limited compared to certain competitors.
The Alpha E-Tec Plus 38kW Combi boiler combines power, efficiency, and user-friendly controls to offer optimal heating performance. It is ideal for larger homes or properties with higher heating demands, providing ample heating output and a reliable supply of hot water.
The boiler’s energy efficiency helps homeowners save on energy costs while ensuring comfort throughout the year.
While it may have a larger physical size and higher initial cost, the Alpha E-Tec Plus 38kW Combi boiler is a reliable and efficient choice for those seeking a high-output heating solution for their home.
Baxi 600 36kW Combi
The Baxi 600 36kW Combi boiler is a powerful and compact heating solution designed to deliver reliable heating and hot water for residential properties. With its high output and efficient performance, it offers enhanced comfort and convenience.
Pros:
- High Heating Output: The Baxi 600 36kW Combi boiler provides a high heating output, making it suitable for larger homes or properties with increased heating demands.
- Compact Design: It features a compact design, allowing for easy installation in tight spaces and making it an ideal choice for properties with limited available space.
- Energy Efficient: The boiler boasts excellent energy efficiency ratings, helping homeowners reduce energy consumption and lower their utility bills.
Cons:
- Limited Warranty: The warranty provided for the Baxi 600 may be shorter or more limited compared to some other models.
- Noise Levels: Some users have reported increased operational noise with the boiler, which could be a consideration for those seeking a quieter heating system.
- Compatibility Limitations: The boiler may have specific compatibility requirements, which could restrict its use with certain heating system setups or accessories.
The Baxi 600 36kW Combi boiler combines power, compactness, and energy efficiency to provide reliable heating and hot water solutions. It offers a high heating output, making it suitable for larger properties or households with higher heating demands.
The compact design allows for easy installation even in limited spaces. The boiler’s energy efficiency helps homeowners save on energy costs while ensuring optimal comfort.
While it may have some limitations in terms of warranty, noise levels, and compatibility, the Baxi 600 36kW Combi boiler remains a reliable and efficient choice for those seeking powerful heating capabilities in a compact package.
This is a powerful yet compact boiler built in the UK providing a powerful 15 l/min hot water flow rate
Ideal Logic C35
The Ideal Logic C35 boiler is a reliable and efficient heating solution designed to provide dependable performance and optimal comfort for residential properties. With its high-quality construction and advanced features, it offers an excellent heating experience.
Pros:
- Impressive Hot Water Flow Rate: The Ideal Logic C35 boiler boasts a generous hot water flow rate, ensuring an abundant supply of hot water for larger households or properties with higher hot water demands.
- Compact Design: It features a compact and space-saving design, making it suitable for installation in properties with limited available space.
- User-Friendly Interface: The boiler is equipped with a user-friendly interface, allowing homeowners to easily control and adjust settings for personalized comfort.
Cons:
- Limited Availability of Spare Parts: Some users have reported challenges in finding or obtaining spare parts for the Ideal Logic C35 boiler, which may cause inconvenience or delays in case of repairs or maintenance.
- Professional Installation Recommended: Due to its advanced features and capabilities, professional installation is recommended to ensure proper setup and optimal performance.
- Higher Initial Cost: The Ideal Logic C35 boiler may come with a higher upfront cost compared to certain other models, which may be a consideration for budget-conscious buyers.
The Ideal Logic C35 boiler delivers reliable heating and hot water solutions with its impressive hot water flow rate and compact design. It is particularly suitable for larger households or properties with higher hot water demands, ensuring a constant supply of hot water.
The user-friendly interface allows for easy control and adjustment of settings, putting comfort in the hands of homeowners. While spare parts availability may be limited, and professional installation is recommended, the Ideal Logic C35 boiler remains a reliable and efficient choice for those seeking a powerful heating solution that meets their hot water needs.
The very popular Logic range also features the most installed boiler in the country. With a powerful 14.5 l/min flow rate, it’s great for a large household.
Worcester Bosch 8000 Style 35kW Black
The Worcester Bosch 8000 Style 35kW Black boiler is a premium and stylish heating solution designed to provide reliable performance and advanced features for residential properties. With its sleek design and cutting-edge technology, it offers both aesthetics and functionality.
Pros:
- Enhanced Connectivity: The Worcester Bosch 8000 Style boiler offers advanced connectivity options, allowing homeowners to control and monitor their heating system remotely for added convenience and energy management.
- Quiet Operation: Users have reported that the Worcester Bosch 8000 Style boiler operates with minimal noise, ensuring a peaceful living environment.
- Extended Warranty: This boiler model may come with an extended warranty, providing homeowners with long-term peace of mind and protection.
Cons:
- Higher Price Point: The Worcester Bosch 8000 Style boiler is positioned at a higher price range compared to some other models, which may be a consideration for budget-conscious buyers.
- Complex Installation: Due to its advanced features and capabilities, professional installation is recommended to ensure proper setup and optimal performance.
- Limited Availability of Certain Colors or Styles: The availability of the black variant or specific design options may be limited in certain regions or markets.
Product Overview: The Worcester Bosch boiler combines style, connectivity, and high performance for a premium heating experience. It adds a touch of elegance to any home with its sleek design and black finish. With advanced connectivity features, homeowners can conveniently control and monitor their heating system from anywhere.
The quiet operation ensures a comfortable and peaceful environment. While it may have a higher price point and require professional installation, the 8000 Style boiler offers advanced functionality, extended warranty options, and a visually appealing design, making it an excellent choice for those seeking both performance and style in their heating system.
A stylish and compact boiler from one of the best known brands in the UK. Delivers a good 14.3 l/min flow rate, and has many other features included.
A comparison of water flow rates
| Combi boiler model | Water flow rate (in litres per minute) |
| Viessmann Vitodens 111-W 35kW | 18.4 |
| Alpha E-Tec Plus 38 kW | 15.9 |
| Baxi 600 36 kW | 15 |
| Ideal Logic C35 | 14.5 |
| Worcester Bosch 8000 Style 35kW | 14.3 |
How to adjust the flow temperature rate on your boiler
- Locate the controls on your combi boiler that allow you to adjust the flow rate. This is usually symbolized by a little picture of a radiator or tap and can be adjusted using up and down arrows.
- Use the buttons to reduce the temperature setting on the display. It is important to only select the heating temperature option and not the hot water temperature.
- Lower the flow temperature on your combi boiler to the minimum recommended flow rate for your make and model of the boiler. The minimum flow rate for a combi boiler ranges from 9-12 litres per minute (LPM).
- Wait for a few days to see if the changes have made a difference to your gas bill. If you notice a reduction in your gas usage, you have successfully adjusted the flow rate on your combi boiler and are saving money on your gas bill.
- If you are unsure about how to adjust the flow rate on your combi boiler or have any concerns, it is always best to consult a qualified heating engineer for advice.
By following these simple steps, you can adjust the flow rate on your combi boiler and save money on your gas bill while reducing your carbon footprint.
Buying Guide
When purchasing a combi boiler with a high water flow rate, there are several key factors to consider. These factors will ensure that the chosen boiler meets your household’s hot water demands effectively:
Water Flow Rate
The primary consideration is the boiler’s water flow rate, which determines how much hot water it can deliver per minute. Look for a boiler with a high flow rate, typically measured in litres per minute (LPM), to ensure an abundant supply of hot water for multiple outlets simultaneously.
Output Capacity
The boiler’s output capacity, measured in kilowatts (kW), indicates its heating power. While focusing on water flow rate, ensure that the chosen boiler has a suitable output capacity to meet both your heating and hot water demands. Higher output capacity generally correlates with a higher water flow rate.
Efficiency Ratings
Energy efficiency is an essential aspect to consider. Look for boilers with high efficiency ratings, usually indicated by ErP (Energy-related Products) labels or ratings. Opting for a highly efficient combi boiler will not only help reduce energy consumption but also save on utility bills.
Size and Space
Consider the size and available space for installation. Some boilers with high water flow rates may have larger physical dimensions. Ensure that the chosen boiler can fit comfortably within your designated space, taking into account any clearance requirements for maintenance and ventilation.
Brand and Warranty
Research reputable brands known for producing reliable and durable boilers. Check the warranty period offered by the manufacturer, as longer warranties can provide added peace of mind regarding potential repairs or replacements.
Summary
Water flow rate is one of the most important factors when choosing a combi boiler. These are some of the best combi boilers for high water flow rates:
- Alpha E-Tec Plus 38W
- Baxi 600 36kW
- Ideal Logic C35
- Viessmann Vitodens 111-W
- Worcester Bosch 8000 Style 35kW
*The information in this article should be used for general guidance only and not as financial advice. Full details are on the link in the footer to our disclaimer page. Always discuss your requirements with a competent and suitably qualified professional before undertaking any work.
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