Underfloor Heating with Gas Boilers - Pros, Cons & Costs

While a heat pump is the most common system used with underfloor heating, is it possible to stick with a combi boiler and if so, what are the costs? 

In this guide, we’ll discuss whether you can have underfloor heating with a combi boiler and how this would compare with a heat pump-underfloor heating setup. 

Let's explore...

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Is It Possible to Have Underfloor Heating with a Combi Boiler?

Yes - you can run underfloor heating with a combi boiler.

However, you’ll usually need a few tweaks:

• A two-port valve to stop your boiler from heating radiators and UFH at the same time (otherwise it can overheat and lock out).

• Correct boiler sizing – your combi must have enough power output (kW) to cover the radiators + UFH load. Sometimes, that means upgrading to a higher-output model.

• Controls and zoning – UFH works best at lower flow temperatures (around 35–45°C), so blending valves and sometimes a small buffer tank are required to regulate temps separately from your radiator circuit.

Pros and Cons of Underfloor Heating with a Combi Boiler

So, what are the arguments for and against having underfloor heating added with a combi boiler?

In this guide, we’ll lay out the pros and cons to help give you a sense of whether it’s the right choice for you.

Pros of UFH with a Combi Boiler:

• Lower upfront cost – much cheaper than installing a heat pump.

• Less disruption – avoids the major works needed for an ASHP/GSHP install.

• Hybrid flexibility – you can keep radiators upstairs while using UFH downstairs.

Cons of UFH with a Combi Boiler:

• Higher running costs – gas combis are less efficient than heat pumps. Expect higher bills long term.

• Extra kit needed – two-port valves, blending valves, possibly larger radiators, and careful zoning.

• Efficiency gap – heat pumps can be up to ~40% more efficient than a boiler + radiator system when paired with UFH.

Will I Need to Upgrade my Combi Boiler?

If you do opt for a combi boiler-underfloor heating setup, you may need to have your existing boiler replaced with a larger model.

By larger, we are referring to the power output and not necessarily the physical size of the boiler. 

It will also need a suitable flow rate. What’s more, modulation capacity is also relevant as a suitable modulation will enable improved efficiency.

Getting the ideal boiler can make sticking with a combi boiler a more sensible option, hence, there’s a good chance you’ll find yourself upgrading your boiler.

The best way to approach this is to consult with a qualified heating engineer to help determine what sort of combi boiler would be a good match for the underfloor heating system you wish to have installed.

Of course, they’d also need to factor in radiator use, if you’d prefer a hybrid approach (i.e., using underfloor heating and radiators). 

One notable advantage of taking a hybrid approach is that by opting for radiators in one area of your home (e.g., upstairs), there’s a good chance that the overall cost of the setup will end up lower.

This is especially so you can avoid the need to have your radiators replaced with larger units (more on that in the next section).

Why Might I Need Larger Radiators?

For a hybrid approach, larger radiators may be required. If you wish to use underfloor heating and radiators, there are two ways to make it work.

On the one hand, you may need larger radiators so that they can run at a lower flow temperature. This is because larger radiators have a lower flow temperature.

Since underfloor heating runs at a relatively low flow temperature, matching the radiator’s temperature to that of the underfloor heating is one way to make a hybrid system work.

Alternatively, you could in theory run the radiators at a high temperature and underfloor heating at a lower temperature.

However, they would need to be separated with various valves to create distinct zones.

Obviously, if opting for this solution, you’d need to verify with the heating engineer that everything is considered for a suitable setup.

Cost of Underfloor Heating with a Combi Boiler

The price of having this system established will depend on a wide range of factors.

Firstly, the size and type of underfloor heating used will play a major role in shaping the price.

Beyond that, it will cost more to have an existing property renovated for an underfloor heating installation than to have one fitted to a new build property.

As for the use of a boiler, whether or not you’ll need to have it replaced will obviously shape the total cost too.

Then you’d need to take into account whether or not you wish to use radiators and whether your existing ones would need replacing.

As mentioned, a hybrid system should cost less overall.

Aside from the above points, the price of labour will vary depending on where you live, ease of access to the work area and the complexity of the installation work.

Lastly, the cost will also be shaped by the quality of the appliances used (e.g., a high-end combi boiler vs. a budget-friendly option).

Here are the average costs of different underfloor heating-combi boiler setups: *

• Dry Underfloor Heating with House Renovation and New Combi Boiler - £3,800 to £8,800

• Wet Underfloor Heating with House Renovation and New Combi Boiler - £7,800 to £17,300

• Dry Underfloor Heating in a New Build Property and New Combi Boiler - £2,500 to £5,300

• Wet Underfloor Heating in a New Build Property and New Combi Boiler - £4,800 to £10,800

*These prices cover the range of costs for different underfloor heating systems based on their size.

If you were to stick with an existing combi boiler, it would reduce the overall cost by approximately £800 to £2,800.

As for the use of radiators, again a hybrid approach is likely to prove less costly too.

Should I Opt for a Combi Boiler or Heat Pump with Underfloor Heating?

The best option for you will depend on a wide range of factors.

For example, if you are more concerned with long-term savings, a heat pump may very well prove a worthy investment.

However, if you want to reduce upfront costs, opt for a combi boiler.

On average, an air source heat pump usually costs between £12,000 and £17,000 to have installed.

On the other hand, it would likely cost around £15,000 to £25,000 to fit a ground source heat pump.

With that being said, if you are based in England or Wales you may be eligible for a £5,000 to £6,000 reduction in the total cost through the Boiler Upgrade Scheme (BUS).

There are pros and cons to each option. Therefore, you should carefully weigh up these points before choosing between a combi boiler and a heat pump.

If you’re stuck, you may want to consult with a qualified heating engineer for tailored advice.

Bottom Line

Yes - you can pair a combi boiler with underfloor heating. It’s cheaper upfront than a heat pump and can work well, especially in a hybrid system.

But it’s not as efficient long term. If you can stretch the budget (and access grants), a heat pump with UFH is usually the smarter investment.

Either way, always consult a qualified heating engineer to size your system and design it properly.

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