Best Combi Boiler For a 3 Bedroom House (Buying Guide)

If you’re looking for a new combi boiler for a 3 bedroom house, this 5-minute guide has everything you need to know to make that all important purchase decision.

We’ll cover what KW output you need, explain what compact combi boilers are, and even give you an idea of how much the installation cost for your new boiler is likely to be.

What KW Combi Boiler You’ll Need For A 3 Bedroom House

Sizing up a boiler isn’t particularly easy. One 3 bedroom house is going to have different hot water and heating demand than the next. Your property might have tonnes of 1.6m radiators and two showers, whereas another might have much smaller 1.2m radiators, and just one shower.

And, that’s why so many installers prefer to do a site visit to spec a property, before determining which is the most suitable boiler.

As a minimum, you’ll want 24kw output for hot water. You’ll get that with a boiler like the Worcester 25i, but it also gets 25kw of central heating output.

For properties that have a higher demand for hot water (a large 3 bedroom house, or one with lots of large radiators), a boost in central heating output is going to be crucial. So, 24kw output for hot water is fine, but you’ll want closer to 30kw output for central heating; you’ll get that with the Worcester 30i.

If you have higher than normal hot water demand, you’ll need a boost on both central heating and hot water output; around 30kw. For that, you’ll need something like the 29CDi Classic Combi; that gets 30kw on central heating, and 30.8kw on hot water.

As you can see, this isn’t a one-size-fits-all approach.

To get ensure you get the most suitable boiler recommended, you can use this boiler sizing calculator. It’s going to consider both hot water and heating demand (based on questions you answer about your property), and give you suitable boilers and prices on screen automatically.

It’s most likely the Worcester 25i is suitable if you live in a small 3-bedroom property, with low-medium hot water and heating demand. You’ll go for the Worcester 30i if you need additional heating demand. And, for those needing a boost on hot water and heating, the 29CDi Classic combi boiler would be a good choice.

The details we plugged into the sizing calculator meant the 25i was the cheapest option:

Installation Area

But, the Worcester 25i isn’t going to be suitable if you need to fit the boiler into a small installation area, such as a kitchen cupboard. In fact, none of the boilers mentioned above will be. They’re better suited to more open installation areas such as airing cupboards, garages, or being wall-hung.

So, if you want to save space in your 3 bedroom house, what’s the best route forward? You’ll need a “Compact” boiler.

For example, you’ll notice if you scroll through the boiler options after filling out your details, the 25Si Compact Combi boiler, and the 30Si Compact Combi boiler.

These are the compact versions of the 25i and the 30i. Essentially, they’ll fit in a kitchen cupboard, and the 25i/30i boilers, won’t.

Which Boiler Brands Are The Best?

We’re mentioning Worcester Bosch a lot here, and that’s because most homeowners either know the brand, or already have one installed. They’ve also won the Which? Best Buy award multiple years running.

Worcester are a quality brand, but there are others out there worth a mention. So, whilst specific boiler recommendations are hard to make without knowing the exact details of your property, we’ve already created a list of the best boiler makes here, and that’s worth a quick read.

There, we list the likes of Viessmann, Vaillant, Baxi and Potterton, and explain exactly why.


Assuming you’ve picked an online installer or local firm that’s using a quality boiler brand, the focus is then warranty. If you type the name of the boiler make and model into Google, plus “warranty”, you’ll see what’s being offered.

This is where you need to be REALLY careful. Some combi boiler models will only come with 2 years warranty. And in our opinion, that’s just not enough.

5 years would be our minimum recommendation. But, bear in mind there are manufacturers offering 7 or even 10 years. For instance, the boiler calculator we mentioned on HEATABLE will highlight Worcester boilers with a 10 year warranty.

Admittedly, this comes at an extra cost in comparison to a cheaper boiler with a 2 year warranty (£200-300 on an average installation), but those extra years’ worth of peace of mind are certainly worth it.

Installation Costs For Combi Boilers In A 3 Bedroom House

We’d expect a minimum installation cost for a combi boiler with a reasonable warranty to be in the region of £1,800-2,000. That’s if you choose a non-compact boiler in the 24kw range.

A typical example, would be the Worcester 25i, which we’ve found online from £1,770:

Worcester Bosch Greenstar i from Heatable

Expect to pay just over £2,000 installation cost for the 30i (larger heating output), and the same for the Compact version of the 25i, the 25Si.

Will A New Boiler Save You Money?

New boilers are naturally more efficient than older ones. So, if your boiler hasn’t completely given up just yet, you might be on the fence as to whether to repair it, or replace it.

The Worcester 25i, being A-rated, runs at around 94% efficiency, 99.7% when running at 30% capacity or 87.7% when it’s maxed out.

Compare that with an older G-rated boiler, which could be less than 70% efficient (that’s bad, by the way).

What that boils down to, is a potential saving of around £105-200 per year, depending on the size of your property, and the efficiency rating of your current boiler.


In many scenarios, that’s going to mean the savings on your energy bills, could cover monthly finance, if that’s the payment route you choose to take.

What’s Next?

Thanks for reading our guide to combi boilers for 3 bedroom houses.

Still got questions about which is the most suitable boiler for your house? Drop us a line, and we’ll do our best to help you out.

Alternatively, jump over to our boiler replacement page which has more information on getting a new boiler. Or, click directly from our home page to get boiler quotes for your property.



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