Choosing a new boiler can feel overwhelming. There are different types, fuel options and sizes to think about, not to mention efficiency ratings, installation costs and warranties. But once you understand the basics, picking the right boiler for your home becomes a lot simpler.

This guide breaks down everything you need to know, from spotting when it’s time for a new boiler, to understanding types, fuel sources and what size boiler you actually need.

Let’s get into it…

At a glance:

• The right boiler depends on your home size, hot water demand and budget
• Combi boilers are the most popular choice in the UK
• Alternatives like hybrid boilers or heat pumps are growing in popularity
• Boiler size is measured in kilowatts (kW) – go too small, and it won’t cope, too big, and you’ll waste energy

When Is It Time For a New Boiler?

If your boiler is:

• More than 10-15 years old
• Breaking down frequently
• Struggling to heat your home or water
• Inefficient (energy bills creeping up)

…it’s likely time for a replacement.

Modern boilers are far more efficient, so upgrading can cut energy bills and reduce your carbon footprint.

Which Boiler is Best? Comparing Boiler Types

Choosing the right boiler depends on your home, hot water needs and long-term plans. Here’s a breakdown of the main types:

Combi Boilers

Combi (combination) boilers are the most popular choice in the UK. They provide heating and hot water directly from the mains, without the need for a separate water tank.

• Best for: Small to medium-sized homes with 1–2 bathrooms
• Pros: Compact, energy-efficient, no need for tanks, quick installation
• Cons: Can struggle with high hot water demand (e.g. multiple showers at once)

Condensing Boilers

All new boilers in the UK must be condensing. These are not a separate type but a design feature that captures heat from exhaust gases and reuses it, making them more efficient.

• Best for: Any modern home (mandatory)
• Pros: More energy-efficient, lower bills, greener heating
• Cons: Pipe can freeze in very cold weather if not insulated

System Boilers

System boilers heat water for your radiators and store hot water in a separate cylinder, making them a good choice for homes with higher demand.

• Best for: Larger households with multiple bathrooms
• Pros: Provides hot water to several taps at once, no need for loft tanks
• Cons: Needs space for a cylinder, longer installation time

Conventional Boilers

Also sometimes known as regular or heat-only boilers, these use both a hot water cylinder and a cold-water storage tank (usually in the loft).

• Best for: Older homes with traditional heating systems
• Pros: Can supply multiple outlets simultaneously, good for homes with low mains pressure
• Cons: Bulky, needs space for tanks, slower to deliver hot water

Note: Gas boilers are currently being phased out in new builds, with alternatives like heat pumps and hydrogen boilers (in the future) taking their place. You may want to consider this for longer term plans.

Electric Boilers

These run on electricity instead of gas, using heating elements to warm the water. Electric boilers are more common in city centres, making up about 7% of UK boilers (Mintel).

• Best for: Flats or homes without access to mains gas
• Pros: Compact, quiet, zero emissions at point of use
• Cons: Higher running costs than gas

Air Source Heat Pumps

Air Source Heat Pumps take the heat from the air outside and around your home as their main source of energy.

Most buildings can have air source heat pumps fitted, apart from a block of flats. These are usually fitted outdoors, so you need to have some space outside. 

• Best for: Well-insulated homes looking for an eco-friendly alternative
• Pros: Very energy-efficient, low carbon emissions, eligible for government boiler  grants, can save money in the long run, saves space
• Cons: Higher upfront cost, requires good insulation

Ground Source Heat Pumps

Ground Source Heat Pumps extract heat from the ground using pipes buried under the ground outside your home.

To get a ground source heat pump, you will need at least 700Sq metres of outdoor space and relatively heavy groundworks are required.  

• Best for: Homes looking for a low maintenance,  eco-friendly alternative
• Pros: Very energy-efficient, low carbon emissions, eligible for government boiler  grants, cheap to run, low maintenance, long lifespan, quiet
• Cons: Higher upfront cost

Hydrogen Boilers

Hydrogen boilers are more environmentally friendly than natural fuel boilers and have greater efficiency, so you use less fuel and help to reduce your carbon footprint. They work the same way that normal boilers do, running on Hydrogen gas instead of natural gas or oil. 

You can’t get a 100% Hydrogen ready boiler just yet, however research suggests that they’ll be available in the coming years. Some boilers are available with a Hydrogen mix, however they do not offer the same lowered environmental impact as a full Hydrogen boiler will. 

• Best for: Eco-conscious homes
• Pros: Very energy-efficient, low carbon emissions
• Cons: 100% hydrogen boilers not yet available

Hybrid Boilers

Hybrid boiler systems combine a traditional boiler with a renewable heat source, such as an air-to-water heat pump. The heat pump does 80% of the work, while the boiler is a booster when you really need it, like when it’s freezing outside. This results in a flexible system that’s reliable, cheaper to run and kinder on the environment. 

Hybrid boilers are suitable for all homes, but particularly those where a heat pump would struggle to heat the property on its own. These include houses built pre 1960, period properties or any property that has poor insulation or glazing.

• Best for: Homes looking for a balance between eco-friendliness and reliable heating
• Pros: Flexible, energy-saving, reduces carbon footprint, can cut bills long-term, fits with any boiler
• Cons: Higher upfront cost

Boiler Type	Pros	Cons
Combi	Compact, instant hot water, efficient, no tanks needed	Limited for large households or multiple bathrooms
System	Good for multiple bathrooms, no loft tanks, reliable hot water supply	Needs space for a hot water cylinder
Conventional	Works with high demand, good for older homes, reliable with low mains pressure	Bulky, needs tanks, slower to deliver hot water
Electric	Quiet, compact, no gas supply needed, zero emissions at point of use	Higher running costs, less efficient for large homes
Air Source Heat Pump	Sustainable, efficient, government grants available, lower bills long-term	High upfront cost, requires good insulation, outdoor unit needed
Ground Source Heat Pump	Very efficient, low running costs, long lifespan, quiet, eligible for grants	Expensive installation, needs large outdoor space and groundworks
Hybrid	Flexible, energy-saving, reliable in cold weather, lower bills, eco-friendly	Higher upfront cost
Hydrogen	Future-proof, low carbon, efficient	Not yet fully available

Fuel Types

The type of fuel your boiler runs on will depend on what’s available in your area, your home setup and your long-term energy goals. While most UK homes rely on mains gas, there are other options worth considering, including eco-friendlier alternatives.

• Mains Gas – The cheapest and most common option if you’re on the grid 
• Liquid petroleum gas (LPG) – Good off-grid choice, but needs a storage tank and deliveries
• Oil – Oil boilers will be banned in existing homes by 2026
• Electric – Compact and easy to install, but more expensive to run
• Heat – Pumping heat from the air or ground, ideal for well-insulated homes
• Hydrogen – Futureproof systems that can switch to low-carbon fuel when it’s rolled out

What Size Boiler Do I Need?

Boiler size is measured in kilowatts (kW), which tells you how much energy it can produce. The right size boiler depends on the number of people, bathrooms and radiators are in your home.

Household Size	Bathrooms	Radiators	Recommended Boiler Size
1–2 people, flat/small house	1	Up to 10	9-15 kW
3–4 people, medium home	1–2	10–15	18-24 kW
4+ people, large home	2+	15–20+	24+ kW

Tip: Bigger isn’t always better. An oversized boiler will cost more to run without improving comfort. A professional survey is the best way to tell what size boiler you need.

Key Considerations

Consider these important factors before making your final decision…

The Size of Your Home 

The size and layout of your property directly affect the boiler output you’ll need. A small flat will usually be fine with a compact combi, while a large detached house may require a system with higher capacity.

People in Your Home

The more people in your household, the higher the demand for hot water and heating. A couple in a one-bed flat won’t need the same power as a family of five with multiple showers running in the mornings.

Radiators and Bathrooms

Count your radiators and bathrooms to gauge the output needed. As a rough guide, 1–2 bathrooms can often be handled by a combi, but 3+ bathrooms may need a system boiler with a hot water cylinder.

Your Existing Heating System

Switching like-for-like (e.g. combi to combi) is usually cheaper and easier, since it uses existing pipework. Changing to a different type can involve more installation work but may save space or improve efficiency long term.

Energy Efficiency

Newer boilers are far more efficient than older models, saving money on energy bills and lowering carbon emissions. Look for boilers with an ErP ‘A’ rating, or explore hybrid heating or heat pump options for even greener heating.

Budget

Boiler prices vary widely depending on type, size and brand. Beyond the upfront cost, factor in installation, ongoing boiler maintenance and long-term running costs. Oftentimes, spending more on a high-efficiency model pays off in the long run.

Reliability and Longevity

A boiler is a big investment, so it’s worth choosing a reliable brand with strong reviews, good warranty options and a reputation for a long lifespan. Cheaper boilers may save you upfront but could cost more in repairs and breakdowns later.

Compatibility with Smart Controls

All of the boilers that we stock and recommend are compatible with most home smart devices to make controlling your heating simple and easy.

Tips From our Boiler Experts

• Choose a longer warranty of at least 10 years for peace of mind (many of our boilers come with a 12 year warranty)
• Research trusted brands
• Decide where it will sit in your home (kitchen, loft, utility room)
• Use a Gas Safe registered installer

We’ve been fitting and servicing boilers since 1980. All of our installers are Gas Safe registered for both domestic and commercial installations. We’re also OFTEC registered for Oil-fired systems.

We provide no-obligation home visits and quotes with finance options available to spread the cost.

Contact us today to arrange a quote for your new boiler.

FAQs: Choosing a New Boiler

Still not sure which boiler is right for you? The answers to these frequently asked questions might help.

How do I choose the right boiler?

Match it to your home size, hot water demand and budget. A professional survey is the safest bet.

Should I choose a gas or electric boiler?

If you’re connected to the mains, gas is usually cheaper to run. Electric boilers are a good option for smaller homes, flats, or areas without gas supply, but running costs are higher.

What’s the most common type of boiler?

Over half of UK homes have a condensing combi boiler, making it the most popular type. Their efficiency and compact size make them top choice.

How do I calculate what size boiler I need?

Boiler size is measured in kilowatts (kW). The bigger your home and the more hot water you use, the higher the kW you’ll need. For example, a small flat may only need 24kW, while a large family home might need 35kW+. An installer can calculate this accurately.

Is it better to get a higher kW boiler?

Not always. Oversizing wastes energy and money, while undersizing leaves you with poor heating and hot water. The right size is the one that matches your home’s needs.

Can a boiler be too big for a house?

Yes. A boiler that’s too powerful will “short cycle,” switching on and off too often, which reduces efficiency and lifespan.

How many radiators can a boiler power?

A 30kW boiler can usually handle up to 15 radiators. Smaller 24kW boilers cover around 10 radiators, while 35–40kW models can run 20+ radiators.

How much does a new boiler cost?

On average, between £2,000 – £4,000 for a unit and installation, depending on the type, size and brand. Renewable systems like heat pumps can cost more upfront (around £6-8,000 for air pumps and £13,000 for ground pumps, including installation) but save on running costs long term.

References and Further Reading

1. Residential Central Heating and Heat Pumps – UK – 2023, Mintel
2. How much could a new boiler save me?
3. Gas boiler vs heat pump – which is right for you?