Furnace Replacement Cost in the UK: Gas, Electric and Oil Prices

Heating quotes in Britain arrive with a suspicious amount of theatre: a laminated brochure, a "good, better, best" table, and a discount that expires at midnight. Underneath sits a simple sum — a box, a day or two of a registered engineer's time, and parts that cost less than most people assume.

The numbers below are the ones installers actually work to, split into kit and labour. Where the American term "furnace" crops up, the British equivalent in nine homes out of ten is a gas boiler, and the pricing behaves quite differently.

In the US a furnace heats air and blows it through ducts. In the UK that arrangement survives only in a slice of 1960s and 1970s estate housing — Johnson & Starley warm-air units in a hall cupboard, feeding floor grilles. Everywhere else the thing being replaced is a wet system: a boiler heating water that circulates to radiators.

This matters for cost because the two are not comparable. A ducted warm-air unit is niche, with few installers, so it carries a premium; a gas boiler is a commodity fitted by thousands of Gas Safe engineers, and competition keeps prices honest. Before spending anything, check the signs a heating system is genuinely finished and rule out cheap faults with a no-heat troubleshooter.

Supplied-and-fitted totals including VAT, for a straightforward job in a three-bedroom house. London and the South East run 15-25% above the middle of each band; the North East, Wales and Northern Ireland sit at or below the bottom.

• •Gas combi, like-for-like swap in the same position: £1,900-£2,900
• •Gas system or regular boiler with existing cylinder: £2,300-£3,400
• •Regular boiler converted to a combi (cylinder removed, pipework altered): £3,200-£4,600
• •Boiler moved to a different room or into a loft: add £600-£1,200
• •Oil boiler, external condensing unit, like-for-like: £2,800-£4,500
• •Bunded oil tank fitted on a new base: £1,400-£2,600
• •Electric boiler, wall-hung, no flue required: £1,900-£3,200
• •Ducted warm-air unit, direct replacement: £3,600-£5,600
• •Warm-air system converted to radiators and a boiler: £6,000-£10,000

On a straight combi swap the split is close to 55% materials and 45% labour, which surprises people who assume the boiler is nearly all of it. A Gas Safe engineer charges £280-£420 a day across most of England and £400-£600 in London. Lifting floorboards, chasing walls or altering the gas supply pipe pushes the job into a second day — pure labour, almost no material cost attached.

The unit prices below are trade, not retail. Merchants sell to accredited installers at 25-40% off list, and a fair quote passes some of that on rather than billing you the RRP.

• •Budget combi (Ideal Logic Max, Alpha E-Tec): £700-£1,050 trade
• •Mid-range combi (Worcester Greenstar 4000, Vaillant ecoTEC Plus): £1,050-£1,500 trade
• •Premium combi (Viessmann Vitodens, Worcester 8000): £1,400-£2,000 trade
• •Flue kit and any extensions: £80-£220
• •Magnetic system filter, fitted: £110-£180
• •Chemical flush £150-£250; full powerflush £400-£750
• •Gas pipe upgraded from 15mm to 22mm: £150-£450
• •Condensate pump where gravity drainage is impossible: £140-£220
• •Scaffolding for a high flue: £250-£500

Four things account for most of the variation between two quotes on the same house. First, position: keeping the boiler where it is protects the flue route, gas run and condensate fall, and relocating each costs money. Second, the state of the existing system — sludge-blackened radiators mean a powerflush rather than a chemical clean, a £500 swing. Third, gas pipe sizing; a 30kW combi often needs 22mm back to the meter, and an engineer who does not check has not really looked.

Fourth is compliance. In England, Boiler Plus rules require a new gas combi to be fitted with one of four efficiency measures — weather compensation, load compensation, flue gas heat recovery or a smart thermostat with automation and optimisation. That is £150-£350 that legitimately belongs in the quote. Making good afterwards, such as tiles behind an old cylinder, is usually excluded, so ask.

One more thing before you commit: gas boilers carry 20% VAT, while an air source heat pump carries 0% VAT and attracts a £7,500 Boiler Upgrade Scheme grant in England and Wales. That closes the gap enough to be worth checking current heat pump prices rather than assuming a boiler wins over ten years.

Terraced house, Leeds, like-for-like 30kW combi in the same kitchen cupboard. Boiler £1,150, flue kit £160, magnetic filter £120, chemical flush and inhibitor £180, sundries £90. Labour: two engineers, one day, £560. Total including VAT: £2,290 — what a clean, uncomplicated swap should cost.

1930s semi, Bristol, regular boiler and airing-cupboard cylinder converted to a combi. Boiler £1,380, filter and flue £280, cylinder and tank removal £220, pipework alterations £340. Labour: two and a half days, £1,150. Total including VAT: £3,470. The extra day is entirely stripping out and pipework — no additional kit.

Detached cottage, rural Norfolk, external oil boiler and a corroded steel tank. Grant Vortex 26kW £1,850, bunded plastic tank £1,320, concrete base £380, oil line and fire valve £160. Labour: OFTEC-registered, two days, £780. Total including VAT: £4,490. The tank is a third of that bill and is often quoted separately, so check it is in the figure.

A reasonable quote is itemised and boring: it names the boiler model and kW output, states the flush type, lists the filter and controls, and gives labour in days. A suspect quote is one number on headed paper with a discount attached.

• •Check the engineer's Gas Safe registration number on the official register — the card can be borrowed, the register cannot
• •Get three written quotes; discard the extremes and interrogate the middle one
• •A deposit above 25% is unusual on domestic work; staged payment on completion is normal
• •"Price valid today only" is a sales tactic, not a trade practice
• •Building Regulations notification should be included — the installer self-certifies and you get a compliance certificate within 30 days
• •Confirm the warranty is registered in your name, not the company's; accredited installers unlock 10-12 years on Worcester, Vaillant and Ideal
• •If finance is offered, ask for the APR and total repayable. Nought per cent over two years is genuine; 12.9% over ten is a different product

These figures come from quotes collected across England, Wales and Scotland in the first half of 2026, cross-checked against merchant trade pricing. Totals include VAT at 20% and assume an accessible property with a working gas or oil supply; listed buildings and homes needing the meter moved sit outside these bands.

One honest note to finish on. A new boiler cuts a heating bill by 10-20% if the old unit was pre-2005 and non-condensing, and by far less if you are replacing a fifteen-year-old condensing boiler that still works. Draught-proofing returns more per pound spent, and learning to bleed radiators and re-pressurise the system often restores performance people had written off. Replace the boiler when it is genuinely finished, unsafe or unrepairable — not because a salesperson has a target to hit.