When we talk about a boiler, the two things instantly striking our mind are sufficient heating and a lot of money. Whilst the first factor is directly tied to the efficiency and size of your boiler, the second one is irrespective and constant, therefore you won’t like to spend on something that only eats a chunk of your monthly salary.

While buying your new boiler, there are several angles you must be reflecting on your choice from to confirm if it will meet your daily requirements. But what are those “factors”, and how do you know which boiler is the best for your house? Well, that is something we shall discuss in the remaining part of this helpful guide.

Make sure to follow each point carefully to avoid regrets later.


The size of your house and the efficiency of your boiler are two interrelated factors. The model you choose is highly dependable on the water and heat requirements of the house which depends on the appliances like non-he washers from agitators, the requirement of your landscape, and daily consumption by people.

That is, finding a balance between both will play a pivotal role in fulfilling the heating needs of a household. For instance, consider the following information as the base for your size choice:

Conventional boiler for big houses

Conventional boilers not only have considerable storage capacity but are also highly efficient, providing hot water to bigger houses with multiple bedrooms and washrooms.

They have a separate storage tank that provides water at multiple outlets at the same time, meeting your needs efficiently whilst keeping the hot water stored for later use. You have the options to choose between different kW or power options though.

For instance, if you have 10 radiators in the house, a 24-30 kW will work best. However, you can choose between 30-35 kW for ideal results. Additionally, as the whole system here is gravity driven, you will need extra tanks in the loft to ensure an efficient water supply at different outlets.

System Boiler for moderately sized houses

A system boiler is also a good option if you need a heavy-duty, multi-tasking machine that stores and runs water in the radiator at the same time. Moreover, as all the components are contained within one unit, you won’t have a hard time installing them.

However, it needs sufficient mains water pressure to draw water successfully. So just in case you live in a low-pressure area, an extra pump will come in handy.

Combi Boiler

If you live in a scarce spaced apartment, perhaps a combi boiler will be your best bet. It’s a small, efficient, and relatively modern boiler that has on-demand functionality.

This means it will directly draw water from the mains, heat it, and move it to the outlet/radiators when needed.

It also doesn’t need a water pump which is another plus point. However, we would only recommend one of these if your space and needs both lay at the minimum side of the chart.

Calculating boiler size/kW?

The size of the boiler can be identified with the help of different calculators available online. To give a rough idea for people in hurry, the following table can be used as an example:

No. of Radiators Minimum kW size of the boiler
8 radiators 15 kW
12 radiators 21 kW
15 radiators 26 kW
20 radiators 33 kW

And so on…

New system or the old one?

Another huge dilemma involved in installing a new boiler is whether one should keep the existing system or install a new one? Well, this is more of a matter of convenience and cost. If your existing system is fully functional and cost-effective, keeping it would be a wise choice, given that it’s as arduous as costly to completely change the pre-existing system. Not to mention the extra wear and tear it would involve.

The only scenario where we would recommend opting for a new system is if it’s extremely old and doesn’t compliment, or rather refrain you from taking full advantage of the contemporary technologies of modern boilers. You will be filling up the costs in the form of low efficiency and extra bills anyway. Make sure to take care of your boiler condition so that you don’t have to spend thousands of pounds every year on a new one.

Space requirements

As mentioned, the type and size of the boiler depend upon the space available. So just in case you are planning for a relatively bigger option, make sure you have enough room in the house for it to fit in along with the water tank. Otherwise, a combi boiler is the only viable, and perhaps the most practical option left.

Which brand?

We wouldn’t be surprised if one compared choosing a boiler with a thousand-piece jigsaw puzzle. And quite rightly. There are tons of boiler brands operating in London and only a handful of them live up to the claims.

Although the performance of all brands is equal in the starting months, the deterioration in performance is relatively faster in cheap models. And by the end of the 5th year of usage, you’ll start seeing visible signs in the form of low efficiency and higher bills.

Going for Worcester Bosch, Vaillant, and Ideal boilers can be a reliable bet for people in a hurry. With considerably good warranties, extremely efficient functionality, and quiet operation, they have remained (and continues to be) among the most popular and trusted brands among Londoners. Secondly they come with a five to six year warranty so you don’t have to worry about repairing boilers in london.

Which fuel will do best?

With the government emphasizing green energy sources for environmental safety, it’s important to know if certain fuel consumption is permitted in your specified area. However, this also depends upon the availability of the fuels and your economic position. To make your choice easier, below given are some common fuels used for different boilers:


Perhaps the cleanest non-renewable energy powered boilers, run directly on methane supplied from the mains. This is a quite economic and convenient option for people living in a city where gas is available 24/7.


If you reside off the mains grid area/countryside with no gas supply, oil is the main common and popular alternative used by people. Although not the most environment-friendly, budget-friendly, and efficient option out there, it gets the job done. Plus, you will need to make a bit extra room for it to fit in.


Biomass is also an option if you care more about being environmentally conscious and want to contribute to green London. Usually run by pellets, logs, or chips, you will need a flue to let the combustion byproducts escape from the property. It’s an eco-friendly and more efficient option when compared to the oil-powered option.

Which one to go for?

If you live in an area where gas is easily accessible 24/7, then a gas boiler should be your priority with no questions asked. Otherwise, you can choose between the other two options as per your preference. We would suggest going for the biomass powered boiler as it is more environment-friendly, and well, gets the job done. Also, see if you can get a boiler that is compatible with modern power sources such as solar power etc. This is a bonus/optional feature if you want your boiler to coop with future technologies.

Choose the best installer

How good is your boiler positioned and how long it will last, because replacing a boiler is not as easy as removing screws without heads, these are two more interrelated factors. For a boiler to work at its full efficiency and keep working for a longer span without deterioration in functionality, it must be installed in a place where it can constantly dissipate the extra heat. Furthermore, the connections should also be secured correctly to ensure no leakages occur. This is important for maximum efficiency as well as the safety of your family.

This is only possible if you have a highly experienced and professional installer on site. So make sure you choose the best in business. You can follow the following tips for guidance during the process:

  • Search for the top service providers operating locally in your area.
  • Collect quotes from at least 4 service providers.
  • Enquire about them from your neighbours, relatives, and check the online reviews left by genuine customers.
  • Now compare the prices in each quotation and find a middle ground between price and quality. Remember, the cheapest one is always the worst, but the most expensive one isn’t always the best.
  • Always go for a registered organisation instead of independent service providers (until you know a reputed one) as they will make sure to keep their image maintained and attend to even to the smallest concerns.
  • Never be afraid to ask questions before, and during the process for maximum transparency.
Jackson Martin

Jackson Martin, holding a degree in Civil Engineering from the University of Texas, has been a prominent figure in the home improvement sector for over 18 years. He joined our team in 2020, sharing his expertise in renovation techniques, sustainable building practices, and DIY projects. Jackson's previous experience includes working in residential construction management and as a home renovation consultant. He is an advocate for energy-efficient homes and enjoys participating in local marathon events.

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