Choosing a new boiler is one of the bigger heating decisions you’ll make for your home, and getting it wrong can mean cold showers, poor pressure, or paying for pipework you never actually needed. Most homeowners are really choosing between three types of boiler: combi, system, and regular, sometimes called conventional or heat-only. This guide covers how each one works, what they typically cost to install in 2026, how to size one correctly, and which option tends to suit which kind of home, along with the current UK rules that actually affect your decision.
Our Gas Safe registered engineers install and service all three types across Nottingham, Beeston, West Bridgford, Stapleford and Long Eaton, and this guide draws on that day-to-day experience alongside current manufacturer guidance and UK regulations, so you can go into any conversation with an installer already knowing what you need.
The short answer Choose a combi boiler if you have one bathroom and want to free up airing cupboard space. Choose a system boiler if you have two or more bathrooms and want strong pressure from multiple taps at once. Choose a regular boiler only if you already have one, with the tank and cylinder already in place, and you’re simply replacing like-for-like. The rest of this guide explains the reasoning behind each of those, plus sizing, cost and compliance detail most other guides skip. |
A combi, or combination, boiler heats water directly from the mains the moment you turn on a tap. There’s no separate cylinder or tank to wait for, and no loft tank taking up space, which is why it’s the most commonly fitted type of boiler in UK homes today.
A system boiler heats water and stores it in a hot water cylinder, usually in an airing cupboard, but unlike a regular boiler it doesn’t need a separate cold water tank in the loft, since it’s fed directly from the mains and most of the major components are built into the boiler itself.
A regular boiler, also called a conventional or heat-only boiler, needs both a hot water cylinder and a separate cold water storage tank, usually in the loft, which feeds the system by gravity. They’re rarely fitted new these days, but are still common in older properties that already have the tank and cylinder in place.
Feature | Combi | System | Regular (heat-only) |
Hot water source | Heated on demand from the mains | Stored in a cylinder, usually unvented | Stored in a cylinder, fed by a loft tank |
Cold water tank in loft | Not needed | Not needed | Required |
Space needed | Least, boiler only | Boiler plus an airing cupboard cylinder | Boiler, cylinder and loft tank |
Multiple bathrooms at once | Can struggle under heavy simultaneous use | Handles this well | Can work well, but pressure is often lower unless pumped |
Typical UK install cost (2026)* | £1,800 to £3,500 | £2,500 to £5,000 | Varies, usually cheapest as a like-for-like swap |
Best suited to | One bathroom, flats, smaller homes | Two or more bathrooms, busier households | Homes already fitted with a tank and cylinder |
*Costs are a general UK guide only, and will vary by property, boiler brand, and whether you’re switching from one system type to another rather than doing a like-for-like swap. The only way to get an accurate figure for your home is a proper survey and quote.
Before you settle on a type, it’s worth working through a few practical questions. These matter more than brand or price alone:
Boiler output is measured in kilowatts (kW), and getting this right matters, an undersized boiler will struggle to heat your home or keep up with hot water demand, while an oversized one costs more to buy and can run less efficiently. As a rough starting point for combi boilers:
Property type | Typical radiators | Guide combi boiler size |
1 to 2 bed, 1 bathroom | Up to 10 | 24kW to 28kW |
3 bed, 1 bathroom | Up to 12 | 28kW to 32kW |
3 to 4 bed, 2 bathrooms | Up to 15 | 30kW to 35kW |
4+ bed detached, 2+ bathrooms | 15 to 20+ | 35kW to 42kW, or a system boiler sized by heat-loss survey |
A commonly used rule of thumb is around 1.5kW per radiator, plus roughly 3kW for each bathroom, but this is only a starting point. For system and regular boilers, heating output is calculated mainly from a proper heat-loss survey based on your radiators, insulation and room sizes, since the cylinder, not the boiler, handles your hot water storage. We carry out a full heat-loss calculation and site survey as standard before quoting, rather than sizing a boiler off a rule of thumb alone.
Flow rate, measured in litres per minute, is one of the most overlooked factors in choosing a boiler. A combi boiler needs a reasonable incoming flow rate, generally at least 10 litres per minute, to deliver a decent shower without a pump. Older properties, rural areas, and flats on upper floors sometimes have naturally low mains pressure, which can limit how well a combi performs regardless of how many bathrooms you have.
A proper survey includes a flow rate test at your kitchen tap. If your pressure is on the low side, a system or regular boiler, paired with a pressurised or pumped cylinder, can sometimes deliver better real-world performance than a combi, even in a smaller home.
All new gas boilers sold in the UK must meet a minimum efficiency rating, and under Boiler Plus rules for new installations in England, they also need at least one extra energy-saving control, such as a smart thermostat, weather compensation, or flue gas heat recovery. Combi boilers avoid the small standing heat losses that come with keeping a cylinder of water hot, but modern cylinders are well insulated, so in practice the difference in running costs between combi and system boilers is usually modest. Your insulation, radiator sizing, and how well your heating controls are set up generally make a bigger difference to your bills than the boiler type alone.
Before you publish this one The G3 point above states a genuine legal requirement, but please confirm with your engineers that Fahrenheit holds current G3 qualifications before this goes live, and consider adding a line naming your qualified engineer(s) for extra trust and transparency. If it isn’t accurate as written, soften it to ‘ask your installer to confirm they hold a valid G3 qualification’ instead of implying it applies to your own team. |
You may have seen headlines about gas boilers being banned from 2035. That was a previous government proposal, and the position has since changed. Under the Warm Homes Plan published in January 2026, the government confirmed there is no fixed phase-out date for gas boilers already in existing homes. In practice, this means you can still buy, install, and replace a gas boiler like-for-like today, and there’s no legal requirement to remove a working system.
The rules that have genuinely changed apply to new-build homes. Under the Future Homes Standard, new houses built in England from 24 March 2027 must be fitted with low-carbon heating, such as a heat pump, rather than a gas boiler. If you’re weighing up a heat pump instead of a gas boiler for an existing property, the £7,500 Boiler Upgrade Scheme grant is still available to help with the cost, it’s worth asking us whether your home would be a good fit before you decide either way.
As Worcester Bosch Accredited Installers and Baxi Approved Installers, and fitters of Grant boilers for oil-fired systems, we can supply combi, system or regular boilers across all three ranges, so your choice of manufacturer doesn’t have to limit which system type suits your home.
Yes, though it usually costs more than a like-for-like swap, since your loft tank and old cylinder need removing and pipework needs adapting. It’s a popular upgrade for homeowners wanting to reclaim space, but get a survey first to check your mains pressure will actually support a combi.
Yes, this is a common move for households that have grown, or added a bathroom, since their combi was fitted. You’ll need space for a cylinder, usually in an airing cupboard, and the installation will take longer than a straight combi swap.
Not by a large margin. Combi boilers avoid the small standing heat losses of a stored cylinder, but modern cylinders are well insulated, so the practical difference on your energy bill is usually small. Insulation, radiator sizing and your heating controls generally matter more than boiler type alone.
Most combi boilers can run a strong shower without a separate pump, since they work directly off mains pressure. Whether it feels powerful depends on your incoming mains pressure and flow rate, which is exactly what we test before recommending a boiler.
Most gas boilers last around 10 to 15 years with regular annual servicing, whether they’re combi, system or regular. Poor water quality, missed services, or a boiler working harder than it should because it’s undersized can all shorten that lifespan.
Once the loft tank and cylinder are removed as part of a combi conversion, that space is freed up completely. Many homeowners turn the old airing cupboard into storage and use the extra loft space for insulation or belongings.
Not usually. Most radiators work with any boiler type, provided they’re in good condition and correctly sized for the room. We check for sludge, balancing issues and sizing as part of the installation, and will flag anything that needs attention.
If you mean solar thermal panels for hot water, yes, a system boiler’s cylinder can be pre-heated by solar before the boiler tops up the rest, which a combi can’t do in the same way. If you mean solar PV panels for electricity, that’s a separate consideration and works alongside any boiler type.
A vented cylinder is fed by gravity from a cold water tank in the loft, typically used with regular boilers. An unvented cylinder is fed directly from the mains under pressure and doesn’t need a loft tank, which is common with system boilers. Unvented cylinders must be installed and maintained by a G3-qualified engineer, as required by Building Regulations, because they store water under pressure.
Not for existing homes. Following the Warm Homes Plan published in January 2026, there’s no fixed date for removing a working gas boiler from a home that already has one, and you can still install a new gas boiler today. The main change affects new-build properties, which must use low-carbon heating instead of a gas boiler from 24 March 2027 under the Future Homes Standard.
Whichever type suits your property, getting the sizing, pressure and compliance right matters far more than the badge on the front of the boiler. If you’d like a straight answer for your own home, book a free survey with one of our Gas Safe registered engineers. We’ll check your pipework, test your water pressure, and recommend the boiler that actually fits how your household uses hot water, not just the cheapest option to fit.
Choosing the right boiler for your home is a big decision, especially if you’re upgrading an old system or fitting one for the first time. Your choice will impact your heating efficiency, water pressure and how much space the system takes up. At Fahrenheit Plumbing and Heating, our experienced team is here to help you decide whether a boiler installation for a combi or system boiler is the best fit. With qualified plumbers across Nottingham, Beeston, West Bridgford, Stapleford and Long Eaton, we can guide you through every step of the process.
A combi boiler, short for combination boiler, is a compact unit that provides both central heating and hot water on demand. It doesn’t require a separate water tank or cylinder, making it ideal for smaller homes or properties with limited storage space. Hot water is heated directly from the mains, which means there’s no waiting time and less energy waste.
System boilers also provide hot water and heating but use a separate hot water cylinder for storage. Unlike conventional boilers, they do not need a cold water tank in the loft, which makes them more efficient and easier to install. System boilers are ideal for homes with multiple bathrooms or higher hot water demand.
Combi boilers are generally wall-mounted and take up very little space. They’re a great option for flats or smaller properties where storage is limited. System boilers, on the other hand, require space for a hot water cylinder, often housed in an airing cupboard.
If you need hot water from multiple taps or showers at the same time, a system boiler is likely the better option. A combi boiler may struggle to keep up with simultaneous demand, especially in larger households.
A combi boiler installation is often quicker and more straightforward, especially when replacing a similar model. System boiler installations can take a little longer and may require additional pipework, especially if you’re switching from a combi.
Both systems are energy efficient, but combi boilers typically use less energy overall because they only heat water when it’s needed. System boilers can be more efficient for homes with frequent hot water use, as the stored hot water can be drawn from instantly.
If you live in a smaller property with one bathroom and are looking to save on installation costs and space, a combi boiler is likely the best fit. If you own a larger home or a rental property with multiple bathrooms, a system boiler offers better performance for higher water demand.
It’s important to get professional advice before making a final decision. At Fahrenheit Plumbing and Heating, we assess your household size, water usage, and existing setup to recommend the most suitable option.
As experienced heating engineers and plumbing professionals serving Nottingham and surrounding areas, we provide honest guidance and expert installations tailored to your home. Whether you need a simple combi boiler swap or a full system boiler upgrade, our qualified team ensures the work is carried out efficiently and to the highest standard.
Still unsure which boiler is best for your home? Contact Fahrenheit Plumbing and Heating for expert advice or to book your boiler installation. We proudly serve Nottingham, Beeston, Long Eaton, West Bridgford and Stapleford with reliable service and transparent pricing.
Let us help you choose the right boiler and keep your home warm all year round.