Biofuel and HVO in Oil Boilers: Which Boilers Accept HVO, OFTEC Guidance and Future-Proofing for Net Zero

Summary

HVO (Hydrotreated Vegetable Oil) is a paraffinic diesel produced from waste vegetable oils, animal fats, and in some cases algae or forestry residue. Unlike fatty acid methyl esters (FAME / biodiesel), HVO is produced through hydrotreatment — a process that removes oxygen and produces a fuel very similar in properties to mineral diesel and, for heating applications, very similar to kerosene.

The UK off-gas-grid heating market has been watching HVO closely as a potential low-carbon alternative to kerosene that does not require a switch to heat pumps. For rural properties where heat pump installation is prohibitively expensive (solid walls, no suitable ground loop area, remote location, high electrical grid upgrade costs), HVO represents a practical decarbonisation pathway using existing heating infrastructure.

The government's Heat and Buildings Strategy acknowledges HVO as part of the transition toolkit for off-gas-grid properties. OFTEC has been actively developing the technical framework for HVO adoption, including training programmes and an HVO approval register of compatible boilers and components. As of early 2026, the list of HVO-approved boilers is growing, but it does not include all models — engineers must check the specific boiler against the manufacturer's HVO approval documentation before switching fuel.

Key Facts

• HVO designation — paraffinic diesel per BS EN 15940; also referred to as "HVO100" when 100% pure; distinct from FAME biodiesel (BS EN 14214), which is NOT suitable for oil boilers
• Carbon reduction — lifecycle CO₂ savings of 70–88% compared to fossil kerosene, depending on feedstock; ISCC-certified HVO from verified feedstocks is required for maximum carbon credit claims
• No tank modification — HVO is fully miscible with kerosene; can be mixed in any ratio; tanks do not need cleaning before switching (though a clean tank is best practice)
• Burner settings — most boilers run on HVO without adjustment; some manufacturers require a nozzle change (typically one size down) due to slightly lower calorific value; flue gas re-analysis required
• Approved boilers (as of 2026) — Worcester Bosch, Viessmann (selected models), Grant (selected models), Warmflow (selected models), Firebird (selected models) have issued HVO approvals; check individual model documentation
• FAME biodiesel — NOT suitable for domestic oil boilers; causes seal degradation, filter blockage, wax at low temperature; do not confuse with HVO
• B10 blend — some boiler manufacturers approve blends up to 10% FAME (B10) but very few approve B100; HVO100 is a separate, superior product
• HVO re-commissioning — OFTEC engineers must re-commission on HVO, carry out flue gas analysis, and update OFT105 to record new fuel type
• Cost — HVO currently costs approximately 20–30% more than kerosene (price fluctuates with feedstock market); no government subsidy comparable to BUS for heat pump conversions is currently available specifically for HVO
• Availability — HVO for heating is distributed by a growing number of UK fuel suppliers; not universally available in all rural areas — check local delivery network before committing a customer to the switch
• Government position — the UK government has not mandated HVO for off-gas-grid heating, but it is included in low-carbon heat roadmaps; future policy could change the subsidy landscape
• OFTEC HVO guidance — OFTEC Technical Bulletin HVO-1 covers engineering requirements; OFTEC maintains an HVO-approved product list

Quick Reference Table

Detailed Guidance

Understanding the Difference: HVO vs Biodiesel vs Kerosene

The confusion between HVO and biodiesel (FAME) is the most important point for any oil heating engineer to get right. They are completely different products:

Kerosene (Class C2): A petroleum distillate; the standard domestic heating fuel. Flash point ≥38°C, very light viscosity, excellent cold-weather performance.

HVO (Hydrotreated Vegetable Oil / paraffinic diesel): Produced by reacting vegetable or waste oils with hydrogen at high pressure. The hydrotreatment process removes oxygen and produces straight-chain hydrocarbons very similar to diesel and paraffinic kerosene. It is chemically quite similar to kerosene but has a slightly higher flash point and slightly higher viscosity. It can be blended with kerosene in any ratio. It does NOT degrade rubber seals, and it does NOT gel in cold UK winters (pour point approximately −30°C).

FAME biodiesel (B100, B20, B10): Produced by transesterification of vegetable oils. Contains oxygen in the molecular structure (as ester groups). This causes: rubber seal degradation over time, filter blockage from wax formation in cold temperatures, storage stability problems (FAME absorbs water and degrades biologically within months). FAME is NOT suitable for domestic oil boilers. Some manufacturers permit up to 10% FAME blend (B10) in mineral diesel systems, but B100 or B20 must never be used in a domestic oil boiler.

The key check on site: if a customer is switching from a "biofuel" source, confirm which product is being supplied. HVO is clear and appears similar to water-white diesel. FAME biodiesel is typically amber/yellow and has a faint vegetable oil smell. Always obtain the fuel's specification sheet and confirm it meets BS EN 15940 (HVO) before recommending it for a boiler not specifically approved for FAME.

Which Boilers Are HVO-Approved?

OFTEC maintains an HVO approval product list, but manufacturers issue their own individual approvals. The engineering process is:

1. Check the specific boiler model against the manufacturer's HVO approval documentation (usually available on the manufacturer's website or OFTEC's HVO portal)
2. Confirm the boiler model, year of manufacture, and current burner specification — approvals may not cover all production years or burner variants
3. Check whether the approval requires any modification (nozzle change, burner setting adjustment)
4. Contact the manufacturer's technical helpline if in doubt — do not assume HVO approval extends to models not explicitly listed

As of 2026, boiler manufacturers that have issued HVO approvals for at least some models include:

• Worcester Bosch (selected Greenstar Oil models)
• Grant (selected Engineering boilers)
• Warmflow (selected models)
• Firebird (selected Enviromax models)
• Viessmann (selected Vitorondens models)

This list is expanding — check current manufacturer guidance, as approvals are being issued on an ongoing basis.

Boilers that are NOT approved for HVO should not be switched to HVO fuel. The consequences of using HVO in a non-approved boiler include: potential warranty voidance, possible seal degradation (some older seals are not compatible with paraffinic fuels at HVO's slightly elevated viscosity), and combustion settings that may not produce optimal efficiency on HVO without adjustment.

The OFTEC HVO Commissioning Process

When an engineer switches an existing oil system from kerosene to HVO, the following steps are required under OFTEC guidance:

Step 1 — Confirm boiler HVO approval: Check the model against the manufacturer's approved list. Obtain written confirmation of approval if needed.

Step 2 — Advise the customer: Inform the customer of the fuel cost difference, current availability in their area, and the fact that the boiler manufacturer approves HVO for their model. Issue a written record of the advice.

Step 3 — Check for required modifications: Some manufacturers require a nozzle change when switching to HVO. If required, fit the specified nozzle.

Step 4 — Check tank and filter condition: HVO is a cleaner fuel than kerosene and can dissolve deposits left by years of kerosene use. Inspect the tank, fuel filter, and strainer before and after the first HVO delivery — a filter change within the first 2–4 weeks of running HVO may be needed.

Step 5 — Re-commission with flue gas analysis: Run the boiler and carry out a full combustion analysis. Record CO₂, O₂, CO, flue temperature, and Bacharach smoke number. Adjust burner settings as required.

Step 6 — Update OFT105: Record the new fuel type (HVO) on the commissioning certificate. Issue a new certificate.

Step 7 — Advise on next service: The first annual service after switching to HVO should include a filter inspection and combustion re-check.

HVO and the Boiler Upgrade Scheme (BUS)

At present (2026), HVO is not a qualifying technology for the Boiler Upgrade Scheme. BUS vouchers are only available for heat pumps (ASHP, GSHP) and biomass boilers in certain rural locations. Switching from kerosene to HVO does not attract any government grant.

However, the government's own Future Homes Standard consultations and Heat and Buildings Strategy documents acknowledge that HVO and other low-carbon liquid fuels may play a role in the off-gas-grid decarbonisation pathway. Future policy may include financial incentives for HVO — watch for announcements from DESNZ (Department for Energy Security and Net Zero) and OFTEC.

Some energy companies and carbon offset providers offer carbon credits for switching to certified HVO, which can partially offset the higher fuel cost. These schemes vary considerably in quality and should be assessed carefully.

Future-Proofing Arguments for and Against HVO

Arguments for recommending HVO to customers:

• Immediate, significant carbon reduction (70–88% lifecycle) using existing heating infrastructure
• No disruption to the home (no radiator changes, no new electrical service)
• Compatible with existing thermostat, controls, and hot water cylinder
• Miscible with kerosene — transition can be gradual (partial blends)
• Viable option for properties where heat pump retrofit is impractical or very expensive
• Can coexist with a solar PV and hot water generation strategy

Arguments against / cautions:

• Higher fuel cost than kerosene (20–30% premium, subject to change)
• Limited local availability in some areas — not all fuel suppliers can deliver HVO
• No government grant currently available
• Heat pumps are the primary government-supported decarbonisation route — future policy may favour heat pumps with stronger incentives, making HVO less economically attractive long-term
• Not all boilers are approved — cannot be universally recommended without model check

Frequently Asked Questions

Can I put HVO in my oil tank without any preparation?

HVO is miscible with kerosene and can be mixed in any ratio. In principle, you can switch directly without tank cleaning. However, HVO's slightly different solvent properties can loosen deposits that have built up with years of kerosene use. A tank in poor condition may release sludge into the fuel system after switching. Best practice is to inspect the tank and clean if there is visible sludge before switching to HVO — see oil tank inspection maintenance.

Does HVO produce the same heat output as kerosene?

HVO has a slightly lower calorific value than kerosene: approximately 43.1 MJ/kg vs. 43.5 MJ/kg for kerosene. In practice, this difference is negligible in terms of domestic heating output. The boiler's thermostat controls heating to the set point — you will not notice any practical difference in warmth. The slightly lower calorific value is one reason some manufacturers specify a slightly larger nozzle size for HVO than for kerosene.

My customer asks if HVO is "carbon neutral" — is it?

Not carbon neutral, but significantly lower carbon than kerosene. ISCC-certified HVO from verified waste or residue feedstocks achieves 70–88% lifecycle carbon reduction. This accounts for the CO₂ emitted during combustion (roughly similar to kerosene per litre) minus the carbon captured in growing the original feedstock. The certification matters — uncertified HVO or HVO from food-crop feedstocks has a different (lower) carbon saving. For a customer making a genuine environmental decision, ask the supplier for their ISCC certification and feedstock declaration.

Will HVO be cheaper in future?

Potentially, as production scales up and UK infrastructure develops. Currently HVO is produced primarily in Europe (Finland, Netherlands, Germany) and imported. UK production capacity is growing. As off-gas-grid decarbonisation policy develops, there may be duty incentives or subsidies that improve HVO's cost position. No specific prediction can be made, but the trajectory for kerosene (which will increasingly be subject to carbon pricing as the UK moves towards net zero) is upward; HVO pricing may converge.

Regulations & Standards

• BS EN 15940:2016+A1:2019 — paraffinic diesel fuels from synthesis or hydrotreatment; the standard HVO must meet for boiler use

• Building Regulations Approved Document J — combustion appliances and fuel storage; fuel change requires re-notification/re-commissioning

• OFTEC Technical Bulletin HVO-1 — OFTEC guidance on HVO use in oil heating systems; HVO approved product register

• ISCC (International Sustainability and Carbon Certification) — certification scheme for verified low-carbon HVO feedstocks

• Heat and Buildings Strategy (BEIS/DESNZ, 2021) — UK government strategy acknowledging HVO's role in off-gas-grid decarbonisation

• OFTEC: HVO guidance and approved boiler list — primary technical resource for HVO boiler compatibility

• Renewable Energy Association: HVO for heat — industry body guidance on HVO in the UK heating market

• GOV.UK: Heat and Buildings Strategy — government policy context for low-carbon liquid fuels

• BSI: BS EN 15940 — paraffinic diesel fuel standard

• kerosene vs gas oil — fuel types and their properties: kerosene vs gas oil vs HVO context

• oil to heat pump changeover — alternative decarbonisation route for off-gas-grid properties

• oil boiler service procedure — annual service checklist; includes notes on HVO systems

• oftec competent person scheme — OFTEC registration and notifiable works for fuel type changes