Helpful Guide to Choosing the Right Boiler for Your Home

Choosing the correct boiler for your home is a long-term decision. The UK’s four top-selling boiler brands claim that their products have an average lifespan is between 10 and 15 years.

Selecting the right boiler for your home means installing a reliable, energy-efficient unit that will keep you warm and save you money for over a decade of use.

However, selecting the right boiler can be complicated, with so many models, types, brands, and other factors to consider.

While choosing the right boiler can be complicated, there are several steps you can take to ensure you’ve selected the correct one for your home.

Let’s start with step one, which is knowing what boiler type is installed in your home.

Step One: Know What Type Of Boiler You Need

Currently, the three most popular types of boilers sold in the UK are:

• Combination (Combi) Boilers
• Heat Only (AKA Regular or Conventional) Boilers
• System Boilers

Each of these boiler types is best designed and suited for specific homes.

Combi Boilers

A combi boiler is a single unit that provides heating and hot water. It is the most commonly installed unit in the UK, with some sources estimating that up to 80% of UK homes have one.

Combi boilers do not require separate storage tanks as they heat water directly from the mains, delivering hot water on demand.

There are both advantages and disadvantages to installing a combi boiler.

Combi Advantages

• Instant Hot Water and Heating: Combi boilers provide hot water on demand, so there’s no waiting for a tank to heat up.
• Space-Saving Design: They don’t need a separate hot water cylinder or cold water tank, making them perfect for homes with limited space.
• Easier Installation: Only one unit needs to be installed, which can reduce installation time and cost.
• Highly Efficient: Most modern combi boilers are over 90% efficient, helping you get more heat for your money.
• Lower Energy Bills: Many homeowners notice a drop in energy costs thanks to their efficiency.
• Easy Maintenance: Combi boilers are standard, so nearly all engineers are trained to repair and maintain them.
• Fresh Water Supply: Water comes directly from the mains rather than a storage tank, so it’s fresher and cleaner.

Combi Boiler Disadvantages

• Water Pressure Depends on Mains Supply: A combi boiler may struggle to perform if your mains water pressure is low or inconsistent.
• Reduced Flow When Demand Is High: Water pressure and temperature may drop if multiple taps or showers are used simultaneously.
• Not Compatible with Power Showers: Combi boilers don’t work with power showers, which rely on hot and cold feeds from a tank-based system.
• More Complex Internals: Because combis combine heating and hot water in one compact unit, there are more components that could potentially fail.

A combi boiler is perfect for smaller homes or flats with one to two bathrooms, up to 10 radiators, and moderate hot water demand.

Heat Only (Regular or Conventional) Boilers

Heat-only boilers, known as regular or conventional boilers, are usually considered one of the older types still commonly found in UK homes.

They are called Heat Only because they supply hot water only for your central heating system, not directly for taps, baths, or showers.

Heat-only boilers work with a separate hot water cylinder and a cold water storage tank, typically installed in the loft. When you turn on a tap or run a bath, the hot water is drawn from the cylinder, not the boiler.

The cold water tank is filled from the mains supply and feeds into the hot water cylinder, where a heat exchanger in the boiler warms it up. A pump sends the hot water through the central heating system to supply radiators, taps, and showers.

There are some advantages and disadvantages to using a heat-only boiler.

Heat Only (Regular or Conventional) Boiler Advantages

• Generally Cheaper to Replace: Heat-only boilers tend to cost less to replace, especially if your home already uses this setup, though prices can fluctuate with demand.
• Supports Multiple Hot Water Outlets: These systems are ideal for homes with more than one bathroom, as they can supply hot water to multiple taps at the same time without pressure issues.
• Not Dependent on Mains Pressure: Since they use a storage tank, they don’t rely on high mains pressure to deliver strong flow.
• Backup Hot Water Option: Many systems include an electric immersion heater in the hot water cylinder. If the boiler breaks down, you can still access hot water using the immersion element.

Heat Only (Regular or Conventional) Boiler Disadvantages

• Lower Efficiency: Compared to combi boilers, they’re less efficient due to losing heat while storing water in the cylinder.
• Requires More Space: These systems need both a hot water cylinder and a cold water tank, often located in the loft, making them unsuitable for smaller properties.
• Delayed Hot Water Supply: You must wait for the water cylinder to heat up before using hot water.
• Limited Hot Water Supply: Once the stored hot water runs out, you must wait for the tank to refill and reheat.
• Potentially Higher Installation Costs: If your home doesn’t already have a hot water tank and pipework, installation can be more complex and expensive.

Generally, heat-only boilers are perfect for larger households with more than one bathroom and low water pressure from the mains.

System Boilers

While they also use a hot water cylinder like heat-only boilers, system boilers differ in several ways. The main difference is that a system boiler doesn’t need a cold water storage tank, as it takes water from the mains.

Also, unlike older heat-only models, the central unit houses many of the system’s boiler components, such as the pumps and valves.

System boilers heat water and store it in a separate hot water cylinder, ready for use. Gas Safe registered engineers consider this type of boiler easier to install. They also free up loft space, as they don’t require a cold water tank and draw water directly from the mains.

System Boiler Advantages

• Compact Design: With most key components built in, system boilers take up less space than traditional setups.
• Quicker Installation: Fewer external parts mean more straightforward and faster installation, especially in homes already designed for modern heating systems.
• Suitable for Multiple Bathrooms: System boilers, like heat-only boilers, can supply hot water to multiple taps simultaneously.

System Boiler Disadvantages

• Dependent on Mains Pressure: System boilers, like combi boilers, rely on consistent mains water pressure. Low-pressure areas may experience reduced performance.
• Requires Cylinder Space: A hot water cylinder still needs room, which may be a limitation in smaller properties.

System boilers are perfect for larger homes with multiple bathrooms and access to good water mains pressure.

Now that we understand the different types of UK boilers, it’s time to review the next step in choosing the right boiler for your home.

Step 2: Considering Your Home’s Size And Hot Water Needs

The right boiler for your home will depend on its size and occupants’ hot water needs.

Generally, the larger the floor space in your home, the more radiators are needed to keep it warm, requiring a larger boiler.

Another factor that will directly affect your boiler choice is how well-insulated the property is.

A well-insulated home retains heat, so your boiler will not have to work harder to maintain a desired heat level.

For larger homes with multiple bathrooms (or high hot water demand), boilers must support a flow rate of 15+ litres per minute (LPM) for consistent hot water across taps and showers.

To calculate your LPM, use a jug, bucket, or container with a known volume, ideally one marked in litres.

1. Turn on the tap to full flow and use a stopwatch or timer to measure 60 seconds.
2. If you collected 5 litres in 60 seconds, your flow rate is 5 litres per minute (L/min).

For homes with lower water pressure, you can always install a home booster pump or an unvented pressurised cylinder to store hot water.

It’s best to consult a qualified Gas Safe registered engineer to determine which solution will best suit your home.

Step 3: Check Energy Efficiency Ratings

When selecting a new boiler for your home, its energy efficiency is essential for several reasons, including:

• Lowering energy bills
• Reducing carbon emissions
• Less wear and tear on the system
• Being compliant with government regulations

The boiler’s Energy-related products (ErP) directive is an EU-led energy labelling system required on all UK boilers.

Based on their fuel consumption, boilers are rated from A+++ (most efficient) to G (least efficient).

• A-rated boilers typically have 90% plus efficiency, meaning less fuel is wasted.
• A G-rated boiler, by comparison, may only be 60–70% efficient, meaning up to 40% of your fuel goes unused and lost as heat.

By law, all new gas boilers in the UK must be at least 92% efficient under the current Building Regulations.

Upgrading your boiler from a G-rated unit to an A-rated one could save a homeowner residing in a typical semi-detached UK home up to £300–£350 per year, depending on fuel prices and usage patterns.

Also, when reviewing your new boiler’s energy efficiency ratings, other features you will want included are:

• Weather compensation (adjusts heating based on outdoor temperature)
• Smart controls and thermostats for better energy management
• Condensing technology that recycles waste heat from flue gases

Step 4: Choosing The Right Output Rating (kW)

A boiler’s kilowatt (kW) rating indicates how much energy it can deliver to heat your home and provide hot water.

The higher the kW rating, the more heat the boiler can generate, ensuring your home stays warm and your hot water supply keeps up with demand.

Choosing the correct boiler size is crucial for comfort and energy efficiency. It’s not just about going bigger:

• An undersized boiler will constantly struggle, resulting in lukewarm radiators, insufficient hot water, and discomfort during peak usage.
• An oversized boiler will cycle on and off too frequently, wasting energy and inflating your utility bills.

To size your boiler correctly, you’ll need to consider:

• The number of radiators
• The number of bathrooms
• Your home’s insulation quality
• The overall floor area

Matching your boiler’s kW output to your home’s needs ensures your system runs efficiently, keeps energy bills in check, and avoids unnecessary strain on the unit.

As a rough guide for selecting the correct kW-sized boiler:

• 24–30 kW: 1–2 bedroom homes
• 30–35 kW: 3–4 bedroom homes
• 35–42+ kW: 4+ bedroom homes with high hot water usage

Ask a qualified heating engineer to assess your needs if you’re ever confused.

Step 5: Consider Installation And Maintenance

Ask any Gas Safe registered engineer for their opinions, and they will share which boilers are easy to install and maintain.

Often, engineers will advise their clients to purchase certain boiler brands, with the most notable ones being:

• Worcester Bosch
• Vaillant
• Viessmann
• Ideal
• Baxi

Another element to remember is whether your boiler is supported by good after-sales service and warranties. Which again will tie in with certain brand reputations.

Step 6: Set A Budget

While it can be tempting to select the cheapest boiler, these units are often not designed to last as long as their more expensive counterparts.

When setting your budget, remember that it should also include all the ownership costs. These ownership costs include:

• Purchase price
• Installation fees
• Maintenance costs
• Energy usage

It’s important to remember that your boiler may remain in use for the next 10 to 15 years, as your maintenance and energy usage costs will be larger than the unit’s upfront costs.

As you can tell, there’s a lot to consider when choosing the right boiler for your home. Luckily, WarmZilla has an easy solution just for you.

easy survey to find the exact boiler you need for your house.

Contact one of our many call centre professionals who want to discuss their brand options.