Green Boilers: Types, Costs, Pros & Cons

If you’re a UK homeowner or landlord searching for green boilers, this guide covers the main low-carbon heating options, how they operate, typical installation and running costs, advantages and drawbacks, maintenance needs, and leading models on the market to help you make an informed choice.

Consider requesting a new boiler quote from Boilers 2 Go early in your planning process. Their specialists can evaluate your property’s suitability for low-carbon heating upgrades and provide accurate quotes that factor in available government grants.

What Are the Main Types of Green Boilers Available in the UK?

The main types of green boilers available in the UK primarily include air source heat pumps (ASHPs), ground source heat pumps (GSHPs), and to a lesser extent biomass boilers and emerging hydrogen-ready systems. 

Air source heat pumps extract heat from outdoor air and are the most popular for residential properties due to easier installation. Ground source heat pumps draw stable heat from the ground via buried loops or boreholes and offer higher efficiency. 

Biomass boilers burn sustainable wood pellets or logs but require fuel storage. Hydrogen-ready boilers (currently mostly 20% blend compatible) are still in limited rollout, with full 100% hydrogen models not yet commercially widespread for domestic use.

How Do Green Boilers Work?

Green boilers work by transferring heat rather than generating it through combustion in most cases. Air source and ground source heat pumps use a refrigeration cycle with a compressor, evaporator, and condenser to extract low-grade heat from air or ground and upgrade it to higher temperatures for central heating and hot water. 

The refrigerant absorbs heat at low pressure, compresses to raise temperature, and releases heat indoors. Biomass boilers combust renewable fuel to heat water directly, while hydrogen-ready boilers combust hydrogen gas (or blends) with oxygen to produce heat and water vapour as the only byproduct.

What Are the Pros and Cons of Green Boilers?

Green boilers deliver substantial benefits but also present challenges. 

Pros of Green Boilers (Air Source & Ground Source Heat Pumps)

• Exceptional energy efficiency — Achieve COP ratings of 3–5, meaning 3–5 units of useful heat for every 1 unit of electricity used, far surpassing traditional gas boilers.
• Significantly lower carbon emissions — Produce much less CO₂ than gas or oil boilers, supporting UK net-zero targets and future-proofing your home.
• Eligibility for generous government grants — Qualify for the £7,500 Boiler Upgrade Scheme grant (England & Wales, 2026), substantially reducing upfront costs.
• Quieter operation — Modern heat pumps run with minimal noise (often 40–55 dB), making them less intrusive than older gas boilers or external condensers.
• Potential for cooling in summer — Many reversible air source heat pumps can provide air conditioning or passive cooling, adding year-round comfort.
• Lower long-term running costs — With good home insulation, underfloor heating, and time-of-use/off-peak electricity tariffs, annual bills can match or beat gas heating.
• Improved EPC rating — Installing a green boiler often boosts your property’s Energy Performance Certificate score by 1–2 bands, benefiting landlords under MEES regulations and increasing sale/rental value.
• No annual Gas Safe servicing required — Reduces mandatory compliance checks compared to gas boilers (though annual MCS/F-Gas maintenance is still advised for warranty and efficiency).

Cons of Green Boilers (Air Source & Ground Source Heat Pumps)

• Higher upfront installation costs — Typically £8,000–£15,000 for air source (before grant) and £20,000–£30,000+ for ground source, even after the £7,500 BUS grant.
• Slower heat-up times — Take longer to warm radiators and rooms compared to gas boilers, especially in poorly insulated properties.
• Requirement for system upgrades — Often need larger radiators, low-temperature radiators, or underfloor heating to deliver heat effectively at lower flow temperatures (35–55°C).
• Reduced efficiency in very cold weather — Performance drops below certain outdoor temperatures (though latest models maintain good output down to -15°C or lower).
• Dependence on electricity prices — Running costs are tied to electricity tariffs; without off-peak or smart tariffs, bills can be higher than gas in some scenarios.
• Need for adequate home insulation — Works best in well-insulated homes; older or poorly insulated properties may see limited savings or require extra upgrades first.
• Installation disruption — Requires outdoor unit placement, possible groundworks (for GSHP), and internal pipework/radiator changes, which can cause more disruption for tenants or occupants.
• Space requirements — Air source units need external wall or garden space with good airflow; ground source needs land for loops or boreholes.

How Much Do Green Boilers Cost to Install and Run in the UK?

Green boilers cost £8,000–£15,000 installed for air source heat pumps in a typical 3–4 bedroom UK home before grants, reducing to £500–£7,500 net after the £7,500 Boiler Upgrade Scheme grant (available in England and Wales as of 2026, running until at least 2028). 

Ground source heat pumps range from £20,000–£30,000+ before the same £7,500 grant. Running costs for well-installed ASHPs typically fall between £800–£1,500 per year for an average home (depending on insulation, tariffs, and usage), often comparable or lower than gas boilers with time-of-use electricity tariffs. 

Biomass systems add ongoing fuel costs of £500–£1,000 annually. Factors such as property size, existing radiator suitability, and hot water demand influence total expenditure.

What Maintenance and Servicing Do Green Boilers Require?

Green boilers require regular maintenance to ensure efficiency and longevity. Annual servicing by an MCS-certified installer or F-Gas registered engineer is recommended (or required for warranty), including checks on refrigerant levels, electrical components, filters, and the outdoor unit for debris or damage. 

Homeowners and landlords should clean or replace air filters every 3–6 months, monitor the system via the controller for error codes, and arrange periodic ground loop inspections for GSHPs. Unlike gas boilers, there is no annual Gas Safe check needed, but record-keeping supports compliance for rental properties and warranty claims.

Which Green Boilers Are Considered the Best on the UK Market?

The best green boilers on the UK market in 2026 feature reliable cold-weather performance, strong warranties, and high efficiency. Top air source heat pump models include the Mitsubishi Ecodan (excellent low-temperature operation and quiet running)

• Vaillant aroTHERM plus (high COP and smart controls)
• Daikin Altherma 3 (reliable with good hot water integration)
• Samsung EHS Mono (compact and efficient)
• Aira heat pumps (strong guarantees for consistent indoor comfort). 
• Leading brands such as Panasonic, LG, and Viessmann also rank highly for homeowners and landlords seeking MCS-approved systems eligible for grants.

FAQs

Can green boilers be installed in flats or apartments?

Yes, air source heat pumps can often be installed in flats with external wall or balcony space for the outdoor unit, though planning permission or freeholder consent may be required, and shared ground loops are sometimes used for ground source systems in multi-occupancy buildings.

How do green boilers affect my property’s EPC rating?

Installing a green boiler such as an air source heat pump can significantly improve your EPC rating (often by 1–2 bands), helping landlords meet MEES requirements and potentially increasing property value or rental appeal.

Are there specific electricity tariffs recommended for green boilers?

Time-of-use tariffs like Octopus Agile or Economy 7 are often best for heat pump green boilers, allowing cheaper overnight or off-peak electricity rates to minimise running costs while running the system efficiently.

Do green boilers provide hot water as well as space heating?

Most modern green boilers, particularly heat pumps with integrated cylinders or thermal stores, provide reliable domestic hot water, though some systems require supplementary immersion heaters during peak demand or very cold periods.

What happens to a green boiler installation if I sell my home?

Green boiler installations generally add value and appeal to buyers, with the remaining warranty transferable in many cases, though buyers may request demonstration or servicing records during the sale process.

This guide equips UK homeowners and landlords with essential knowledge about green boilers to support sustainable home heating decisions. For personalised recommendations, request a new boiler quote from Boilers 2 Go today.