Heat Pump vs. Gas Boiler: A Complete Guide

In the debate of heat pump vs. gas boiler, choosing the right heating system is a decision with lasting impacts on your comfort, wallet, and even the environment. As heating technology evolves, homeowners face a pivotal choice: stick with the time-tested reliability of a gas boiler, or embrace the eco-friendly efficiency of a heat pump? Each system has strengths and trade-offs, and understanding these can help you make a decision that meets both immediate needs and future goals. For the purpose of this article heat pump refers to an air to water heat pump.

Understanding the Basics of Heat Pumps

A heat pump is an efficient system for heating and cooling your home by transferring heat from one place to another, rather than generating it directly. It functions much like a reversible air conditioner: in winter, it extracts heat from the outside air (even when it’s cold) and brings it indoors; in summer, in some cases it can do the reverse, pulling heat from inside your home and releasing it outdoors.

Here’s an outline of how it works:

1. Heat Absorption: The core of the heat pump is a special liquid known as refrigerant. This refrigerant circulates through a closed system of coils and, depending on the season, absorbs heat either from outside or inside. When it’s cold outside, the refrigerant absorbs even small amounts of heat from the outdoor air. (Cold doesn’t mean there’s no heat, it simply means there’s less.)
2. Compression and Temperature Increase: The heat pump contains a compressor that pressurises the refrigerant, raising its temperature considerably. This now-hot refrigerant then flows through a coil inside your home.
3. Heat Release Indoors: As the refrigerant moves through the indoor coils, often located in the hot water tank, it releases the heat it collected from outside into your home’s heating system, which then warms your living space. Once the refrigerant cools down again, it circulates back outside to absorb more heat, repeating the cycle.
4. Reversible Process for Cooling: In summer, the process reverses. The refrigerant absorbs heat from inside the house and releases it outdoors, cooling your home. This is more common in air to air heat pumps.

The primary benefit of a heat pump is its efficiency: it can deliver two to three times more heat energy than the electrical energy it uses. This is because it moves heat rather than creating it by burning fuel or directly converting electricity to heat. For homeowners, this can translate to lower energy bills and a reduced carbon footprint, particularly if the heat pump is powered by renewable electricity. If your aim is to reduce your carbon footprint then a heat pump is always a positive move, but ensuring it is financially sensible is also important.

When a Heat Pump Might Not Be the Right Choice

Despite the increasing interest in heat pumps, with their potential for energy efficiency and reduced environmental impact, it can be challenging to sift through the information and make a well-informed decision about whether to install one in your home. A good starting point is identifying scenarios where heat pumps may not be suitable. Doing so not only saves time but also allows for consideration of other heating solutions, either as interim options or long-term alternatives.

The success of a heat pump largely depends on its efficiency, which is optimal when conditions are favourable. Heat pumps generally operate inefficiently in certain situations, such as:

1. Very Low Outdoor Temperatures: Extreme cold significantly reduces the efficiency of a heat pump. As heat pumps rely on drawing existing energy from the air, they are less effective when temperatures drop. Industry standards indicate that -5°C is typically the lower limit for higher efficiency. If your area regularly experiences temperatures below -5°C, the heat pump’s reduced efficiency may outweigh the savings achieved at warmer temperatures. In such cases, an additional backup heating system may be recommended for particularly cold periods. Many people in remote colder locations may also have a wood burning stove for example.
2. High Indoor Heating Requirements: Homes that are very large or poorly insulated often need greater heating, which can strain a heat pump’s efficiency. Traditional radiators in the UK run at 70-80°C, but this high flow temperature can heavily impact the efficiency of a heat pump, which operates best at radiator temperatures between 35-55°C. In fact, there’s a direct relationship between flow temperature and operating costs. Low-temperature systems can be achieved by increasing the surface area of emitters, such as by using underfloor heating or larger radiators. However, this option is only effective in homes that are reasonably well-insulated, as low temperatures will not provide sufficient warmth in poorly insulated spaces. Homes lacking adequate roof insulation, wall insulation, or double glazing may find a heat pump costly and insufficient for warmth, often requiring backup heating. In fact most tanks have an immersion electrical heating coil for those coldest days of the year. The UK government’s Boiler Upgrade Scheme, which incentivises the installation of heat pumps, advises that homes should have good levels of insulation (EPC rating of C or above) before installing a heat pump. If you’re considering a heat pump, and your goal are financial savings as well as carbon savings, it is crucial to first invest in improving the building’s insulation and addressing other energy performance issues. Vaillant provide more guidance on the topic.
3. Low-Energy Homes (e.g., Passivhaus Standard): For homes built to very low-energy standards, such as Passivhaus, the heating demand is so low that a heat pump may not be cost-effective. In such cases, simpler heating solutions, like infrared or electric heating paired with a mechanical ventilation and heat recovery (MVHR) system, may be more practical.
4. Hot Water Demand: Using a heat pump for hot water is less efficient because water heating typically requires higher temperatures, near the upper end of a heat pump’s optimal range. While this alone doesn’t rule out a heat pump, households with very high hot water demands at specific times may find costs increasing. For example, in a household with a large family all needing hot water simultaneously in the morning and a poorly insulated home, the heat pump may struggle to keep up with demand. They are not suited to producing a large about of hot water quickly, a steady increase in temperature is more efficient.

The good news is that the UK’s mild winters make it well-suited to heat pump technology. A well-designed system should comfortably meet the needs of most families. Additionally, with more flexible working patterns, peak demands are often spread out, helping to make heat pump systems even more viable for typical family use. In summary there seems to be good case for holding off on heat pump installation until it can be combined with basic fabric improvements that give a peak heating load below 60 W/m² peak.

High-Impact Considerations for Heat Pumps vs. Gas Boilers

Although several factors influence the comparison between heat pumps and gas boilers, it’s well known that financial considerations have the greatest impact when homeowners are choosing a new heating system. Let’s explore the key differences between the two options and determine which system is the most cost-effective and suitable for your home and lifestyle.

1. Upfront Costs of Heat Pumps vs. Gas Boilers

The upfront cost for a heat pump system can range from £10,000 to £18,000 depending on the size, installation requirements, and the type of system. If we consider a 3 bedroom semi-detached home where a 7kW boiler would typically be required and replace it with a 10kW heat pump, we can consider the price list below as a minimum cost example, as per a recent retrofit project:

Heat pump – £3500

Water cylinder – £850

Labour for survey and installation – £4500

Electronics and thermostats – £900

Additional materials – £1750

Heat emitters 2 (low temperature radiators) – £850

Installing a gas boiler on the other hand is generally less costly, with installation fees around £2,000 to £4,000. The cost is often lower in homes with existing gas lines, making this a more budget-friendly choice for many households, especially if the household was previously heated with a boiler.

Regulatory Considerations and Incentives

Many governments, including the UK, are providing incentives for installing heat pumps as part of the transition to renewable energy. The Boiler Upgrade Scheme is one such initiative designed to make heat pumps more accessible. £7500 is available as a grant which is applied for by the installer. This would reduce the £ 12350 total above to £4850, which is comparable to a new boiler. Regardless even with these incentives a heat pump is going to be more expensive. You have to look at the potentially large operational savings to make the heat pump the financial winner.

External cost

Another talking point for Heat Pump sceptics is the electrical demand on the grid. Both in terms of available energy but also electrical supply to homes. It is true that this has to be considered. The Cibse journal article explains this well. For most small and medium modern homes with typical heating loads a heat pump can be installed right now. There is the rare case for older electrical supplies or particularly energy hungry homes that the supply is not sufficient and energy saving upgrades will be needed or the electrical grid upgraded paid for by the distribution network operator (DNOs). We are seeing this upgrade of the electrical grid pushed also by the advent of electric car chargers. Because of this general trend DNOs are accepting the need to upgrade their system.

2. Comparing Energy Bills

Heat pumps operate on electricity, which, depending on local rates, are typically higher than gas prices. With electricity averaging around £0.34 per kWh and gas at £0.10 per kWh, the operating costs could vary by region. Ofgem explains the current energy price cap put in place due to the serious risk faced by fuel poverty. Heat pumps are known for their high efficiency, with a Coefficient of Performance (COP) often between 3 and 4. Which effectively cuts the cost to a third or a quarter. Given that the cost of electricity is less that 4 times that of gas, heat pumps can still offer 20-30% savings over gas boilers in well designed cases. Note the section ‘When a Heat Pump Might Not Be the Right Choice’. When you consider the cost of electricity should come down relative to gas due to the growing renewable energy sector, this saving will only improve for heat pump with time. There are also savings to be made my removing the gas connection to a home, and therfore your standing charge.

According to British Gas, newer gas boilers typically have an efficiency rating between 80-98% for, condensing models. Whilst old boilers may be as un efficient as 70%. A boiler can deliver heating quickly and with greatly lower efficiency it can deliver it consistent all year round, regardless of outdoor temperatures.

This is not the case for a heat pump of which the performance is not suited to a high output but a steady continuous supply. So a heat pump system has to be designed more effectively. There may very well be some low efficiency days in the year where heating cost would be more than the boiler, but a good designer will know that any relatively losses will be made up with efficient cost saving for the rest of the heating period. Meaning a net financial operating saving for the heat pump.

3. Future-Proofing Your Heating System: Heat Pump or Boiler?

With the global focus on reducing carbon emissions, many regions are moving away from gas boilers in favour of electric and renewable solutions like heat pumps. This trend is likely to continue as governments implement stricter energy regulations aimed at reducing reliance on fossil fuels source. See our blog titled Energy efficiency vs house valuation for more details on changing trends. Some people could argue that there will not be a movement away from fossil fuels, but whilst missing our targets is considered to be illegal, we have to assume the UK will be trying not to break the law.  This will see reduced installation cost due to economies of scale, increased capacity and subsidies.

Mid-Level Considerations for Heat Pumps vs. Gas Boilers

The next two variables we consider medium impact because although they could be deemed important for some situations, whilst for other will typically never make or break a decision.

4. How Long Do Heat Pumps and Gas Boilers Last?

On average, heat pumps last 10-15 years, though proper maintenance can extend this lifespan. In some cases, they can be used for cooling in the summer months therfore they have a longer working period in the year. They also have more moving and variable speed parts that are more sensitive to changing temperatures, consequently they are also more dependent on regular cleaning. While a gas boiler often have a longer lifespan of 15-20 years, with some lasting longer if regularly serviced and maintained.

5. Comparing Space Needs

Heat pumps require both indoor and outdoor units. Whilst the indoor unit is typically of the same size of a combi boiler the additional parts can be cumbersome in smaller homes or apartments. Space needs to be found for an outdoor unit and also a water storage tank if your home does not already have a water tank. Gas boilers are compact and typically installed indoors, often taking up less space and offering greater flexibility in small living spaces.

Minor Factors to Consider When Choosing a Heating System

6. Heat Pump vs. Gas Boiler: Which Needs More Maintenance?

Heat pumps require an annual service much like boilers to maintain optimal performance, particularly in areas with extreme weather. In addition, it is recommended to preform regular simple cleaning several times a year. Such things include cleaning and replacing filters, removing leaves and debris to ensure airflow. Although this additional need to clean is undesirable, In reality it would be akin to other garden task and easy maintenance category much like that of cutting the lawn or washing the car.

7. Environmental Impact of Heat Pumps vs. Gas Boilers?

When powered by renewable electricity, heat pumps produce little to no carbon emissions. Even without renewables, they reduce carbon emissions by up to 60% compared to fossil-fuel-based systems. Gas boilers are carbon-intensive, emitting 2.1 kg of CO2 per cubic meter of natural gas burned. This contributes significantly to climate change and carbon emissions. The cost of climate change has been having an impact on many people around the world for years, and it is becoming increasingly more apparent here in the UK. More regular global conflict, flooding, increased migration and healthcare pressures are just a few.

8. Some people say Heat Pumps are noisy!

Heat pumps can produce noise from the outdoor compressor in the range of 40-60dB, which can be disruptive depending on the setup location. The quieter models are comparable to a low refrigerator hum.  If you live in an area with a low residual noise level for example a rural street with no background noise or distant traffic a heat pump could be disruptive whilst in its vicinity. It is for this reason that regulation do no permit owners to install heat pumps within 1m of the boundary with neighbours. Tactically locating the outdoor unit will make them un noticeable.

A gas boiler is generally quieter as they operate indoors, producing minimal noisem, except when the boiler kick in. But as they are inside, they could be more disruptive than a heat pump if a heat pump is well located. Realistically those who live in a very quiet area, often have space and more flexibility in where the pump is located. Meaning it is less likely to be heard.

9. User Experience and Control

Heat pumps often integrate seamlessly with smart thermostats and zoning systems, allowing for precise temperature control and efficient energy use. Gas boilers are compatible with many smart systems, though they generally offer fewer advanced control options compared to modern heat pumps.

Resolve’s Thoughts: Choosing Between a Heat Pump and Gas Boiler

It seems there is little to separate an air-source heat pump (ASHP) from a traditional boiler when evaluating the options as I have above, particularly if you are simply looking to replace a gas boiler in a poorly insulated home. As suggested by this thought provoking article in the Cibse Journal which pushes even harder for heat pump adoption, the installer will have to balance the need to increase the heat emitter size with added cost; and increase flow temperatures with reduced efficiency, to outweigh the high peak energy demand of the old home.  In such cases, a boiler is often the way to meet high energy demands at a reasonable cost. However, there are two important factors to consider in the next stage of decision-making.

If your home is so poorly insulated you should seriously consider an intervention to reduce your energy demand. Resolve can help determine where your money is best spent. Identifying the significant heat loss areas of your property, building an airtightness strategy and implementing a low-energy refurbishment, will improve the case for a heat pump. And if a heat pump was viable before, the size of the heat pump may be able to be reduced. Heat pumps become increasingly efficient with a low temperature heating system, which improves their performance and reduces the likelihood that a backup heating source will be needed. Resolve can ensure that your home will be optimised to this very case.

Finally, given the long lifespan of a heating system, the increasing environmental impact of continued reliance on fossil fuel-based boilers is hard to overlook. The long-term environmental benefits of switching to a heat pump are substantial, especially as the UK moves towards decarbonisation and a future with reduced reliance on carbon-intensive energy sources. If this is your main motivation then a heat pump is essential as soon as possible. Resolve can calculate your carbon savings for different design choices. This transparency about materials cost and impact allows for informed decision making. For those with the financial means, living in a middle-class home with sufficient space, there is little to deter you from opting for a heat pump and enjoying the advantages it offers.

However, it is unfortunate that access to heat pumps remains difficult for lower-income households. The government should do more to support those with suitable homes by offering financial incentives or assistance to ensure that a wider demographic can benefit from this technology. See our upcoming blog on the sources of finance for sustainable interventions or drop us an email and Resolve can direct you to the source of any government grants, that you may be eligible for. The need for broader access to sustainable heating solutions is critical, as it would help address both the climate crisis and energy affordability challenges faced by many households across the UK. Get in touch to have a preliminary assessment of your energy load, then we can determine if a heat pump is good for you. Keep an eye out for our top tips article for making your heat pump more efficient. it is exactly what you need to know to keep your installer on their toes.

Resolve consultancy can model the energy demand and energy load of your projects and determine such parameters.