Heat Pumps Explained

How Heat Pumps Work

A heat pump moves heat rather than generating it by burning fuel. It works a bit like a fridge in reverse: it collects low-grade heat from outside (air or ground), compresses it to raise the temperature, and then releases that heat into your home’s heating system.

Even cold winter air contains heat energy. The key is the refrigerant cycle and compressor which concentrates that heat into something useful for your radiators and hot water.

The two main types you’ll hear about are:

Air-source heat pumps (ASHP)

These draw heat from the outside air via a fan unit. They are the most common in the UK because installation is usually simpler and cheaper than ground source.

Ground-source heat pumps (GSHP)

These draw heat from the ground through pipe loops buried in trenches or boreholes. They can be more efficient because ground temperatures are more stable than air temperatures, but they need more space and higher installation costs.

You’ll often see performance described as “COP” (coefficient of performance). If a heat pump has a COP of 3, it means it produces roughly 3 kWh of heat for every 1 kWh of electricity used. In practice, performance changes through the year and depends on how well the system is designed and how your home holds heat.

Efficiency in the Real World

Heat pumps are highly efficient, but they are not magic. Real-world efficiency depends on a set of interacting factors:

Outside temperature

Air-source systems work harder in colder weather. They still work, but efficiency can drop.

Flow temperature

Heat pumps operate best at lower flow temperatures (often 35–55°C). The higher the temperature you ask the system to deliver, the harder it works and the lower the efficiency.

Heat loss and insulation

If your home loses heat quickly (poor insulation, draughts), the system has to keep running at higher output.

System design and sizing

A properly designed system matches your home’s heat loss. Undersized systems struggle. Oversized systems can short-cycle (turn on/off too much), reducing efficiency and comfort.

This is why a heat pump installation should include proper heat loss calculations and a design plan, not just “swap boiler for heat pump”.

Why Insulation and Draft Proofing Come First

Heat pumps heat homes differently from boilers. Boilers blast high-temperature water through radiators. Heat pumps provide steadier, lower-temperature heat over longer periods.

That usually means:

• Better insulation improves comfort and lowers running costs
• Draft proofing reduces how hard the system has to work
• A well-insulated home can use a smaller heat pump, reducing upfront cost

If your home is leaky and under-insulated, a heat pump can still work — but you may end up paying more to run it and it may feel less “toasty fast” than a boiler unless the system is designed carefully.

Radiators, Underfloor Heating, and Heat Loss Calculations

Because heat pumps run at lower temperatures, the home’s heat emitters matter.

Radiators

Some homes need larger radiators or additional radiators to deliver the same comfort at lower water temperatures. It’s not always necessary, but it must be assessed room-by-room.

Underfloor heating

This works extremely well with heat pumps because it runs at low temperatures and spreads heat evenly.

Hot water (cylinder)

Many homes will need a hot water cylinder because heat pumps generally heat hot water more slowly than combi boilers. Some systems use an immersion heater to boost hot water temperature when needed.

If an installer isn’t talking about radiator sizing, heat loss calculations, emitter upgrades or hot water setup, that’s a red flag.

Running Costs vs Gas Boilers

Heat pumps are efficient, but electricity usually costs more per kWh than gas. Whether your bills go up or down depends on:

• Your heat pump efficiency (seasonal performance)
• Your home insulation level
• Your electricity tariff
• Whether you can shift usage to cheaper times
• Whether you have solar panels and/or a battery

A heat pump can be cheaper than gas in well-insulated homes on the right tariff, but it can be more expensive in poorly insulated homes with high heat demand.

A useful mental model is:

Running cost depends on the electricity price divided by efficiency.

If electricity is expensive and the system is inefficient, costs rise.

If electricity is reasonable and the system is efficient, costs can be competitive.

Grants and Support (Boiler Upgrade Scheme and Local Schemes)

The Boiler Upgrade Scheme (BUS) provides grants towards eligible heat pump installations, but you must use an MCS-certified installer and meet eligibility criteria.

Boiler Upgrade Scheme

https://www.gov.uk/apply-boiler-upgrade-scheme

Other support may exist locally through councils or retrofit schemes, and some households can access energy efficiency funding which complements heat pump installation (insulation, draft proofing, etc.). When considering a heat pump, it often makes sense to bundle “fabric improvements” and low-carbon heating into one plan.

Noise, Space, and Planning Considerations

Air-source heat pumps have an external unit (like an air-con unit). They do make noise, but modern systems are generally quiet and must meet standards. However, where the unit is placed matters (distance to neighbours, airflow, avoiding enclosed spaces).

You also need:

• External space with airflow
• Internal space for controls and often a hot water cylinder
• Potentially upgrades to pipework, radiators or electrics

In some cases, planning considerations apply, especially for listed buildings or specific property types.

Maintenance, Lifespan, and What “Good” Looks Like

Heat pumps usually need annual servicing and occasional checks. A good installation should deliver:

• Stable indoor temperatures
• Reasonable noise levels
• Clear controls and user guidance
• Transparent performance expectations (not over-promising)

Typical lifespan is often in the 15–20 year range, with good maintenance.

Common Misconceptions (and the Reality)

Heat pumps:

• Do work in UK winters (they’re widely used in colder countries too)
• Do not automatically reduce bills without good system design and a suitable home
• Are not “drop-in replacements” for boilers — the heating system needs designing properly
• Are best thought of as part of a home energy system (insulation, emitters, controls, tariff)