How This Calculator Works
The calculator does two things in one pass: it estimates your likely running-cost savings from a boiler upgrade, and it checks whether your household may be eligible for a free upgrade under ECO4.
Property Analysis
Your property type, age, size and bedroom count are used to estimate your annual heat demand, using the same Typical Domestic Consumption Value (TDCV) approach Ofgem uses to calculate the energy price cap.
ECO4 Eligibility Check
Your EPC rating is checked against ECO4's qualifying bands (D, E, F or G). Because EPC band alone isn't enough to qualify (see below), the next step of the eligibility checker also asks about benefits, income and any household vulnerability, so you get an accurate result rather than a partial one.
Detailed Breakdown
You'll see your estimated annual saving in pounds, an approximate CO₂ reduction, and what your next step should be whether that's a free ECO4 application or a paid upgrade quote.
Bottom line —One pass gives you both a personalised savings estimate and an ECO4 eligibility signal — you don't need a separate form to find out if a free upgrade may be available.
How Much Could You Save With a New A-Rated Boiler?
An A-rated condensing boiler converts roughly 90p of every £1 of gas into usable heat. Many boilers installed before 2005 (when condensing boilers became mandatory) run at only 60–70% efficiency meaning a meaningful share of what you're paying for is being lost up the flue.
Typical annual savings from replacing an old boiler with a new A-rated one:
| Property type | Typical annual saving |
|---|---|
| Detached house | £180–£300 |
| Semi-detached house | £130–£250 |
| Mid-terrace house | £110–£220 |
| Bungalow | £100–£220 |
| Flat / apartment | £50–£150 |
These are estimate ranges, not guarantees your actual saving depends on your current boiler's exact efficiency, your property's insulation, your heating habits, and current gas prices. The calculator above gives you a figure personalised to your answers rather than a generic average.
Over 10 years, savings can add up to a meaningful sum often several thousand pounds for larger or less efficient homes though the exact total depends heavily on the factors above, so treat any single "10-year total" as a rough illustration rather than a promise.
Bottom line —Most UK homes see £100–£300 a year; larger or older, less efficient homes can approach £600. Use the calculator for a figure tied to your answers, not a generic average.
Am I Eligible for a Free Boiler Through ECO4?
Short answer: possibly but your EPC rating alone doesn't decide it. You generally need both of the following:
- Your property has an EPC rating of D, E, F, or G (properties rated A, B or C don't qualify they're already considered energy efficient), and
- You meet one of three eligibility routes:
- You or someone in your household receives a qualifying means-tested benefit (e.g. Universal Credit, Pension Credit, Income-based JSA/ESA, Income Support, Working or Child Tax Credit, Housing Benefit), or
- Your household income is low enough to qualify via your local council's LA Flex scheme (income thresholds and criteria are set by each council individually), or
- A household member has a health condition that's made worse by living in a cold home.
If you're a homeowner or a private tenant with your landlord's written permission, you can apply either way. ECO4 is funded by energy suppliers, not by the government directly, and it's due to close to new applications on 31 December 2026, with the Warm Homes Plan expected to take over from January 2027.
If you don't receive benefits and aren't sure about LA Flex, it's still worth checking LA Flex criteria vary by council and are often wider than people expect. Check your ECO4 eligibility in detail →
Bottom line —EPC D–G is necessary but not enough — you also need a benefits route, LA Flex, or a cold-related health condition. Approval is always subject to survey and available funding.
What If I Don't Qualify for ECO4?
Not qualifying for ECO4 doesn't mean there's nothing available:
LA Flex may still apply even without benefits eligibility depends on your council's own statement of intent. See LA Flex eligibility →
Boiler Upgrade Scheme (BUS) offers a grant toward a heat pump rather than a gas boiler, and isn't means-tested in the same way. Compare heat pump grant savings →
The Warm Homes Plan, expected to replace ECO4 from 2027, may open up new routes. Read about the Warm Homes Plan →
You can also pay for an upgrade privately the savings estimate above still applies, and a new boiler may still be worthwhile even without a grant, especially if your current one is over 15 years old or breaking down regularly.
Bottom line —No ECO4? Check LA Flex, consider BUS for a heat pump, watch the Warm Homes Plan from 2027, or use the savings estimate to decide on a private upgrade.
Will a New Boiler Improve My EPC Rating?
Often, yes but it depends on your starting point. Replacing a very old, non-condensing boiler with a modern A-rated condensing model can add several points to your EPC score, and in some cases is enough to move a borderline property up a full band (for example, F to E, or D to C). The improvement tends to be smaller if you're replacing an already-modern condensing boiler with a newer one.
A boiler upgrade works best as part of a wider improvement pairing it with loft or cavity wall insulation typically produces a bigger EPC jump than a boiler swap alone. Check your current EPC rating for free →
Bottom line —An old non-condensing swap can move you a band; pairing the boiler with insulation usually delivers a bigger EPC gain than the boiler alone.
What Information Do You Need to Use the Calculator?
You'll need:
- Property type (detached, semi-detached, terrace, flat, bungalow) and roughly how old it is
- Number of bedrooms
- Your current boiler's type and approximate age
- Fuel type gas, oil, or electric
Optional, but improves accuracy:
- Your current EPC rating (find it free on the government EPC register)
- Your actual annual gas or energy spend, or kWh usage from a recent bill
- Number of occupants and typical thermostat settings
You don't need any of the optional fields to get a result leave them blank and the calculator will estimate based on typical UK consumption data for your property type.
Bottom line —Property type, age, bedrooms, boiler type/age and fuel are enough — optional kWh and EPC fields only tighten the estimate.
How Accurate Is This Calculator?
The calculator is built on Ofgem's Typical Domestic Consumption Values and the current Ofgem price cap gas rate (7.33p/kWh for Direct Debit customers, Jul–Sep 2026 this is reviewed and updated every quarter when Ofgem changes the cap), combined with standard boiler efficiency ratings for old vs. A-rated systems. Estimates are typically within 10–15% of actual savings for a property matching the assumptions above, though your real result will vary with your specific insulation, heating habits, and local gas price. Entering your actual kWh usage, where you have it, will always give a more accurate estimate than the default averages.
Bottom line —Expect roughly 10–15% accuracy against real bills when your home matches the assumptions; your own kWh figure always beats the default average.
What We Do and Don't Do
FreeBoilerUpgrade.uk is an independent eligibility-check and application-assistance service we're not the government, an energy supplier, or the installer. Here's exactly what that means:
- We check your eligibility against ECO4, LA Flex and related scheme rules, and help you put together the application.
- If you're likely eligible, we connect you with a Gas Safe registered installer from our network to carry out a home survey and, where approved, the installation.
- We can't guarantee approval, a specific boiler brand, or an exact installation date final approval sits with the obligated energy supplier or your local authority, following a home survey.
- The service is free to you: it's funded through the energy supplier/installer network, not by charging homeowners.
You can verify our installer network's Gas Safe registration at gassaferegister.co.uk, and ECO4's rules directly at Ofgem.
Bottom line —FreeBoilerUpgrade.uk is a TrustMark-aware, Gas Safe network ECO4 eligibility and application assistance service operating nationwide across England, Scotland and Wales — not the government, a supplier, or the installer.
What Do ECO4, TDCV, EPC and A-Rated Mean?
- ECO4
- ECO4 is the fourth phase of the UK government's Energy Company Obligation, running until 31 December 2026, requiring large energy suppliers to fund free boiler and heating upgrades for eligible low-income and fuel-poor households.
- LA Flex
- LA Flex (Local Authority Flexible Eligibility) is the route under ECO4 that lets councils nominate households who don't receive qualifying benefits but still meet fuel-poverty, income or cold-related health criteria.
- EPC
- An EPC (Energy Performance Certificate) is a government-issued rating (A–G) of a property's energy efficiency, valid for 10 years. ECO4 typically requires band D, E, F or G.
- TDCV
- TDCV (Typical Domestic Consumption Values) are Ofgem's standard annual gas and electricity usage figures used to set the energy price cap and to estimate household heat demand in tools like this calculator.
- A-rated boiler
- An A-rated condensing boiler is a modern heating appliance that converts roughly 90%+ of fuel into usable heat, versus 60–70% for many pre-2005 non-condensing boilers.
- Ofgem
- Ofgem is the Office of Gas and Electricity Markets — the UK regulator that sets the quarterly energy price cap and administers ECO4 delivery rules for energy suppliers.
- Boiler Upgrade Scheme (BUS)
- The Boiler Upgrade Scheme is a UK government grant toward installing a heat pump (or certain other low-carbon heating) rather than a gas boiler, and is not means-tested in the same way as ECO4.
- Warm Homes Plan
- The Warm Homes Plan is the government's expected successor to ECO4 from January 2027 as the main funding route for home energy upgrades; detailed eligibility rules have not been finalised yet.
Old Boiler vs New A-Rated Condensing Boiler — What's the Difference?
Same home, very different efficiency — and bill impact.
| Factor | Old / pre-2005 boiler | New A-rated condensing |
|---|---|---|
| Typical efficiency | 60–70% | Roughly 90%+ (≈90p of every £1 of gas) |
| Heat lost up the flue | Meaningful share of fuel paid for | Much lower waste heat |
| Typical annual saving if upgrading | — | £50–£300 by property type; up to ~£600 in some cases |
| EPC impact | Often holds a home in D–G | Can add points; sometimes a full band |
| Breakdown risk | Higher on boilers 15+ years old | Lower with modern warranty-backed units |
| ECO4 funding if eligible | N/A (current plant) | £0 to the household if approved |
Bottom line —If your boiler is pre-2005 or regularly breaking down, the efficiency gap alone often makes an upgrade worthwhile — and ECO4 can remove the upfront cost if you qualify.
Related reading: ECO4 eligibility guide, free boiler vs heat pump grant comparison, and EPC rating D–G and ECO4.
Boiler Savings Calculator: Frequently Asked Questions
How accurate is the boiler savings calculator?
It's built on Ofgem's typical UK consumption data and the current quarterly price cap gas rate, and is typically accurate within 10–15% of real-world savings. Entering your actual kWh usage from a recent bill improves accuracy further.
How much can I save with an A-rated boiler?
Most UK households save between £100 and £300 a year, with larger or older, less efficient homes seeing bigger savings up to around £600 a year in some cases. Your exact figure depends on your current boiler's efficiency, property size, and insulation.
Can I get a completely free boiler through ECO4?
Possibly. You need an EPC rating of D, E, F or G and to either receive a qualifying benefit, meet your council's LA Flex low-income criteria, or have a household member whose health is affected by cold housing. EPC rating alone doesn't qualify you.
What happens if I don't qualify for ECO4?
You may still qualify through LA Flex even without benefits, or through the Boiler Upgrade Scheme if you're considering a heat pump instead. If neither applies, you can still get an accurate savings estimate and consider a privately-funded upgrade.
Will a new boiler improve my EPC rating?
Often, yes replacing a very old non-condensing boiler can add several points and sometimes move you up a full band. Combining it with insulation typically gives a bigger improvement than a boiler swap alone.
What information do I need to use the calculator?
Your property type, approximate age, number of bedrooms, current boiler type and age, and fuel type. An EPC rating and recent kWh usage are optional but improve accuracy.
When does the ECO4 scheme close?
ECO4 is scheduled to close to new applications on 31 December 2026. The Warm Homes Plan is expected to take over from January 2027, though full details of its replacement criteria haven't yet been confirmed.
Is this calculator really free, and will I be charged anything?
Yes, the calculator and eligibility check are free with no obligation. If you go on to receive a grant-funded boiler through ECO4, the cost is covered by the obligated energy supplier, not by you.
Are you the government or my energy supplier?
No. We're an independent eligibility-check and application-assistance service. We check your eligibility against government-set scheme rules and connect you with Gas Safe registered installers we don't fund or install the boilers ourselves.
Can private tenants apply, not just homeowners?
Yes, private tenants can apply with their landlord's written permission. The landlord isn't charged for ECO4-funded work, so most agree once they understand there's no cost to them.
Sources & references
Ofgem — Energy price cap unit rates and standing charges
Gas Direct Debit average 7.33p/kWh, 1 July to 30 September 2026
Ofgem — Energy Company Obligation (ECO)
ECO4 runs until 31 December 2026
gov.uk — Energy Company Obligation (ECO4)
Scheme overview for households
gov.uk — Find an energy certificate (EPC register)
Free EPC lookup
gov.uk — Boiler Upgrade Scheme
Heat pump grant route (BUS)
Gas Safe Register
Statutory register for gas engineers
TrustMark — government-endorsed quality scheme
Installer accreditation standard
Energy Saving Trust
Independent guidance on home energy efficiency and bill savings
Published: . Last updated: . Author: Peter Davies, ECO4 Analyst.
Revision log
- — Full content rebuild from the approved editorial brief. Verbatim meta, body, FAQs and Service/FAQPage JSON-LD. Calculator widget retained in place. Added glossary, old vs A-rated comparison, sources list, author bio and HowTo schema. Fact-checked Ofgem Jul–Sep 2026 gas rate (7.33p/kWh) and ECO4 end date (31 December 2026).
- — Page first published with interactive savings calculator.
Summary: The Key Facts at a Glance
Free Boiler Upgrade UK is an independent eligibility-check and application-assistance service helping UK households estimate annual savings from an A-rated boiler upgrade and check ECO4 eligibility nationwide — we are not the government, an energy supplier, or the installer.
Upgrading from an old, inefficient boiler to a new A-rated condensing boiler typically saves a UK household £200–£600 a year on gas. Typical ranges by property type run from £50–£150 for a flat to £180–£300 for a detached house. The free calculator above uses Ofgem TDCV data and the Jul–Sep 2026 price-cap gas rate of 7.33p/kWh.
A free ECO4 boiler needs an EPC of D–G plus a benefits, LA Flex or cold-related health route. Approval is subject to survey and available funding. ECO4 closes to new applications on 31 December 2026. Call 07342 267215 or email info@freeboilerupgrade.uk.