Heat Pump vs Gas Boiler in 2026: Real Running Costs for South East London Homes

Should you keep your gas boiler, or switch to a heat pump? It's the question I get asked more than any other by homeowners across Orpington, Bromley, Sevenoaks and the wider Kent area. There's a lot of marketing noise out there — both for and against — and the honest answer depends entirely on your specific home.

This guide cuts through the spin and gives you the real numbers, from someone who actually services these systems day-to-day. I don't install heat pumps myself, so I have no commercial interest in pushing one option over the other.

The Headline Numbers (Don't Trust These Alone)

You'll see eye-catching claims in the press: "Heat pumps are 4× more efficient than gas boilers!" That's true on paper. A heat pump's COP (Coefficient of Performance) is typically 3–4, meaning it produces 3–4kWh of heat for every 1kWh of electricity it uses. A modern gas boiler is around 90% efficient.

But efficiency isn't the whole story — fuel cost matters more.

• Gas: roughly 6–7p per kWh in 2026
• Electricity: roughly 27p per kWh on a standard tariff

Quick maths: a gas boiler at 90% efficiency costs around 7.5p per usable kWh of heat. A heat pump at COP 3.5 costs around 7.7p per usable kWh. Almost identical on paper.

What Actually Determines Whether a Heat Pump Saves You Money

1. Your Home's Insulation

Heat pumps work best with a steady, lower-temperature heat output (typically 40–50°C flow temperature versus 70°C+ for a boiler). That requires a home that holds heat well. Modern homes built post-2000 are usually fine. Solid-wall Victorian properties without insulation upgrades will struggle and cost more to run.

The honest truth: If your home has poor loft insulation, no cavity wall insulation, and single-glazed windows, fix those first. They'll do more for your bills than any heating system change.

2. Radiator Sizing

Boiler radiators are sized for high flow temperatures. Heat pumps need larger radiators or underfloor heating to deliver the same heat at lower temperatures. Many heat pump installations include radiator upgrades — budget for this if you're getting quotes.

3. Your Electricity Tariff

The single biggest factor most people miss. Standard tariff at 27p/kWh makes heat pumps marginal. A dedicated heat pump tariff with cheaper overnight or off-peak rates can drop your effective electricity cost to 15–20p/kWh, transforming the maths.

4. Hot Water Usage

Heat pumps heat water to lower temperatures than boilers. If you have a large family with high hot water demand, you may need a larger cylinder or different operating pattern.

Real-World Examples from Local Homes

Example 1: 1990s Detached in Petts Wood

Well-insulated, modernised radiators, dedicated heat pump tariff. Previous gas annual cost: roughly £1,800. Heat pump annual cost: roughly £1,250. Saving: ~£550/year. Combined with the £7,500 BUS grant, payback on the additional install cost works out to around 7–9 years.

Example 2: 1930s Semi in Bromley

Cavity wall and loft insulation done, original radiators. Previous gas annual cost: roughly £1,500. Heat pump annual cost: roughly £1,650. Loss: ~£150/year. Without radiator upgrades, the system can't deliver heat efficiently. Recommendation was to delay installation until insulation work was completed.

Example 3: New-Build in Sevenoaks (Underfloor Heating)

Fully insulated to current building regs, underfloor heating throughout. Previous gas annual cost: roughly £1,200. Heat pump annual cost: roughly £700. Saving: ~£500/year. Underfloor heating is the perfect partner for a heat pump.

What the £7,500 BUS Grant Actually Covers

The Boiler Upgrade Scheme (BUS) provides £7,500 towards the cost of a qualifying ASHP installation. A few things to know:

• Must be installed by an MCS-certified installer
• You don't claim it — the installer claims and discounts your invoice
• Typical full ASHP install runs £12,000–£18,000 depending on system size and radiator/cylinder upgrades needed — so the grant typically covers 40–60% of cost
• Property must have a current EPC with no outstanding insulation recommendations

When a Heat Pump Genuinely Makes Sense

Based on what I see in real homes:

• Modern, well-insulated property (post-2000 build, or older with insulation done)
• Existing oversized or modern radiators, or underfloor heating
• Willingness to switch to a heat pump electricity tariff
• Boiler is approaching end of life anyway (10+ years old)
• You value future-proofing your home (gas boilers will be phased out of new builds)
• Long-term ownership planned (10+ years to recover the investment)

When It Doesn't Make Sense (Yet)

• Solid-wall property with no insulation
• Existing boiler is recent and performing well
• Short-term ownership planned
• Original small radiators throughout
• Reluctance to monitor or switch electricity tariffs

The Honest Recommendation

For most homes I see in our area, a heat pump can save money — but only if everything else is right first. If you're in any doubt, get a heat loss survey done by an MCS installer (they're often free), make sure your insulation is sorted, and look hard at your electricity tariff before committing.

And once your heat pump is installed, get it serviced every year. It's the single biggest factor in whether you actually achieve the running cost savings the manufacturer promises.