There are now more heat pump grants available in the UK than at any point in history – yet most homeowners only know about one. The Boiler Upgrade Scheme, ECO4, the Warm Homes Local Grant, Home Energy Scotland, and VAT relief can all be accessed by different households, and in some cases stacked together. If you’re still researching, our heat pump comparison hub covers every decision from sizing to brand selection. This guide explains every active scheme for 2026, who qualifies for each, and exactly how to apply without falling into the trap of scammers or missing out on money you’re entitled to.
FREE QUOTE COMPARISON
Compare Heat Pump Quotes from Trusted Suppliers
✓ £7,500 BUS grant available
£7,500 BUS grant available • MCS-certified installers • 100% free
- The Boiler Upgrade Scheme (BUS) provides £7,500 for air source heat pumps in England and Wales - the most straightforward grant, with no income test and no minimum EPC requirement since the 2025 rule change
- ECO4 covers free heat pumps for low-income households in EPC D-G properties - means-tested via benefits eligibility, with installations fully funded including radiator upgrades and insulation
- Home Energy Scotland offers interest-free loans up to £15,000 for Scottish homeowners - separate from the BUS grant, with cashback grants of £7,500-9,000 available on top of the loan
- The 2025 removal of the EPC insulation prerequisite opened BUS to millions more homes - previously required loft and cavity wall insulation first, now any home with fossil fuel heating can apply
- Your MCS-certified installer applies for the BUS grant on your behalf at point of installation - you do not pay the full price upfront, the £7,500 is deducted before you receive the final invoice
Boiler Upgrade Scheme (BUS) – £7,500 Grant
The BUS pays £7,500 for air-to-water heat pumps and ground source heat pumps, or £2,500 for air-to-air units. There is no income test, and the scheme runs until March 2028.
The Boiler Upgrade Scheme (BUS) is the UK government’s flagship grant for replacing fossil fuel boilers with low-carbon heating. Administered by Ofgem and funded by the Department for Energy Security and Net Zero (DESNZ), the scheme launched in April 2022 and has been extended through to March 2028. Unlike some grants, it is available to any eligible homeowner regardless of income – making it the most accessible route to funded heat pump installation in England and Wales.
Who Qualifies for the BUS?
To qualify for a BUS grant, you must meet all of the following criteria:
Property requirements: You must own the property (including leasehold with landlord consent). It must be your primary residence or a property you let to tenants. Social housing and local authority-owned properties are excluded. The property must have a valid Energy Performance Certificate (EPC) issued within the last ten years.
Existing heating: Your current primary heating system must use fossil fuel – gas, oil, or LPG. Properties already connected to a heat network or district heating scheme do not qualify. Electric storage heaters, direct electric heating, and biomass boilers are also excluded from the qualifying list.
Insulation rule (updated 2025): A significant change came into effect in 2025. The previous requirement – that EPC-recommended insulation measures (loft or cavity wall insulation) must be installed before applying – was removed. Homeowners with an uninsulated property can now access the BUS grant directly, without first completing insulation upgrades. This removed a major barrier that had previously blocked thousands of applications.
MCS-certified installer: The heat pump must be installed by a Microgeneration Certification Scheme (MCS) certified contractor. The installer – not the homeowner – makes the grant application to Ofgem on your behalf. You pay the net cost (after the grant is deducted from the invoice) directly to the installer.
How the Application Process Works
The BUS application is entirely installer-led. You do not need to contact Ofgem directly or fill in a government form. Here is the process:
1. Get quotes from two or three MCS-certified heat pump installers (find them at mcscertified.com). 2. Confirm the installer will apply for the BUS grant on your behalf – reputable installers do this as standard. 3. The installer submits the grant application to Ofgem before the work starts. 4. Installation must be completed within 120 days of the grant being approved. 5. The installer redeems the voucher through Ofgem, and you pay only the remainder of the agreed price.
The entire process is designed to be seamless for the homeowner. If an installer tells you that you need to apply yourself or pay the full amount upfront and claim back later, treat this as a red flag – that is not how the BUS works. Our heat pump buyer’s guide covers 12 practical tips to get right before booking your first survey.
| Heat Pump Type | BUS Grant Amount | Typical Installed Cost | Net Cost After Grant |
|---|---|---|---|
| Air-to-water (ASHP) | £7,500 | £8,000 – £16,500 | £500 – £9,000 |
| Ground source (GSHP) | £7,500 | £15,000 – £35,000 | £7,500 – £27,500 |
| Air-to-air (ASHP) | £2,500 | £4,000 – £9,500 | £1,500 – £7,000 |
| Biomass boiler | £2,500 | £10,000 – £19,000 | £7,500 – £16,500 |
ECO4 – Fully Funded Heat Pumps for Low-Income Homes
ECO4 can cover up to 100% of heat pump installation costs for qualifying low-income households in England, Wales, and Scotland. The scheme runs until December 2026.
The Energy Company Obligation (ECO4) is a government programme that requires the UK’s largest energy suppliers to fund energy efficiency upgrades – including heat pump installation – for low-income and vulnerable households. Unlike the BUS, which is a fixed-amount voucher, ECO4 can cover the full cost of a qualifying installation. However, it is more tightly targeted and requires a lower-rated EPC to qualify. The scheme is administered through energy suppliers such as British Gas, E.ON, and Octopus Energy, and runs until December 2026.
Route 1: Benefits-Based Eligibility
The most straightforward route into ECO4 is via benefits. If any member of your household currently receives one of the following, you may qualify: Universal Credit, Pension Credit (Guarantee Credit), Income Support, Income-based Jobseeker’s Allowance, Income-related Employment and Support Allowance, Child Benefit (income threshold applies – households earning under approximately £31,000 per year), Working Tax Credit or Child Tax Credit (must be receiving the benefit, not just entitled to it), and certain disability benefits including DLA and PIP where income is also low.
You also need a property with an EPC rating of E, F, or G – which means your home is currently below average energy efficiency. An installer or energy supplier will carry out a free survey to confirm eligibility before any work is agreed. There is no up-front cost under ECO4 for qualifying households.
Route 2: LA Flex (Local Authority Flexibility)
If you do not receive qualifying benefits but have a low household income, you may still access ECO4 via the Local Authority Flexibility route (sometimes called LA Flex or ECO4 Flex). Under this route, local councils can declare households as eligible based on their own criteria. The typical income threshold is approximately £31,000 gross annual household income, but councils have discretion.
LA Flex is particularly useful for households that have recently moved off benefits or where income is low but no means-tested benefit is being claimed. Contact your local council’s energy efficiency team or check their website for referral forms – energy suppliers will not always advertise this route proactively.
ECO4 covers England, Wales, and Scotland. Northern Ireland has its own separate schemes (see the NISEP section below). ECO4 is not available in Northern Ireland.
ECO4 is the only route to a genuinely free heat pump installation for low-income households. If your home has an EPC of E, F, or G and you receive qualifying benefits – or your household earns under approximately £31,000 – it is worth contacting your energy supplier directly or using the government’s ECO4 eligibility checker at gov.uk.
FREE QUOTE COMPARISON
Compare Heat Pump Quotes from Trusted Suppliers
✓ £7,500 BUS grant available
£7,500 BUS grant available • MCS-certified installers • 100% free
Warm Homes: Local Grant – Up to £30,000
The Warm Homes Local Grant offers up to £15,000 for a heat pump and up to £15,000 for insulation measures – a combined maximum of £30,000 – for eligible households in England only.
The Warm Homes: Local Grant is the first phase of the UK government’s broader Warm Homes Plan and represents one of the most generous packages of support available for eligible households. Launched in April 2025 and running through to March 2028, the scheme is delivered by local authorities in England and targets low-income households living in inefficient homes. It is separate from the Boiler Upgrade Scheme and from ECO4 – it operates on its own eligibility track.
What Does the Warm Homes Local Grant Cover?
The grant is structured in two parts: up to £15,000 towards a low-carbon heating system (including air source and ground source heat pumps), and up to £15,000 towards insulation measures such as cavity wall insulation, loft insulation, solid wall insulation, and underfloor insulation. A household that qualifies for both elements can receive the full £30,000. The insulation element is intended to bring the property up to a minimum EPC C rating, which also improves heat pump efficiency.
Eligibility Criteria
The Warm Homes Local Grant is available to owner-occupiers and private tenants (with landlord consent) in England. To qualify, households must meet at least one of the following conditions: household income below £36,000 per year, or receipt of a qualifying means-tested benefit such as Universal Credit, Pension Credit, or Housing Benefit. The property must have a current EPC rating of D, E, F, or G. Properties rated A, B, or C do not qualify for the insulation element, though they may still access heating support.
The grant is administered locally, which means availability, application processes, and specific eligibility rules vary by council area. Some councils operate waiting lists due to high demand. The best starting point is to contact your local council’s housing or energy efficiency team, or to use the Ofgem’s Home Upgrade Grant portal at gov.uk/warm-homes-local-grant.
The Warm Homes Local Grant is only available in England, and delivery varies significantly by council area. If you are a low-income household with a poorly rated EPC, this scheme offers the largest potential package of support – up to £30,000 combined. Start with your local council, not a third-party “grant finder” service.
Home Energy Scotland – Grants and Interest-Free Loans
Home Energy Scotland offers a £7,500 grant plus a £7,500 interest-free loan for heat pumps (£9,000 for rural properties). There is no income test – any Scottish homeowner can apply.
Scotland operates a distinct and, in many respects, more generous support framework for heat pumps than England and Wales. The Home Energy Scotland (HES) programme – funded by the Scottish Government and delivered by Energy Saving Trust – provides both grant funding and interest-free loans to homeowners installing renewable heating systems. Crucially, the HES grant is not means-tested: any homeowner in Scotland can apply, regardless of income or benefits status.
HES Grant and Loan Package
Under the current HES framework, eligible homeowners can receive a grant of up to £7,500 towards a heat pump installation, combined with an interest-free loan of up to £7,500 – giving a combined package of up to £15,000. For rural and island properties (defined by the Scottish Government), the loan ceiling increases to £9,000, reflecting the higher costs of rural installation and the greater reliance on oil and LPG heating in these areas. The loan is repaid over up to 12 years with zero interest, making it genuinely comparable to a grant in practical terms.
The HES heat pump grant can be combined with the UK-wide BUS grant in certain circumstances, though you cannot receive both grants for exactly the same item of expenditure – speak to the HES advisory team for guidance on combining support packages for your specific project.
Warmer Homes Scotland – For Fuel-Poor Households
Separately from the main HES programme, Warmer Homes Scotland targets fuel-poor households and can provide fully funded measures including heat pumps, insulation, draught-proofing, and ventilation. Eligibility is based on income and fuel poverty indicators rather than a simple benefits check. Households on low incomes, older residents, and those in poor-condition housing are the primary beneficiaries. Applications go through the same Home Energy Scotland contact point.
To access any Home Energy Scotland scheme, call the free advice line on 0808 808 2282 (Monday to Friday, 8am to 8pm; Saturday, 9am to 5pm). Advisers will assess your eligibility, explain which schemes you can access, and connect you with a local approved installer. There is no online application form – all applications start with a phone or live chat conversation.
Scotland’s Home Energy Scotland programme is the most accessible non-means-tested route to heat pump funding in the UK. Any Scottish homeowner – regardless of income – can access up to £15,000 in combined grant and interest-free loan. Call 0808 808 2282 to start your application.
Wales – Nest Scheme
The Nest scheme in Wales provides free heat pump installation for low-income households with an EPC rating of E or below. Income thresholds are broadly £18,000-£24,000, or qualifying benefits recipients.
Wales operates its own energy efficiency programme called Nest, delivered on behalf of the Welsh Government by British Gas. Nest provides fully funded energy efficiency improvements – including heat pump installation – for eligible households in Wales. It is the Welsh equivalent of ECO4 but operates under devolved Welsh Government policy and has its own separate eligibility criteria.
Nest Eligibility
To qualify for a free heat pump through Nest, you must live in Wales and meet the following criteria: your property must have an EPC rating of 54 (E) or below (properties in bands E, F, or G), and you must either receive a qualifying benefit (Universal Credit, Pension Credit, Child Tax Credit, Working Tax Credit, Income Support, income-based JSA or ESA, Housing Benefit, or DLA/PIP in combination with another benefit) or have a gross household income below the Nest income threshold. The income threshold varies depending on household composition – broadly £18,000 for single adults and up to approximately £24,000 for larger families – though Welsh Government updates these figures periodically.
Eligible measures under Nest include heat pumps, insulation (cavity wall, loft, underfloor, solid wall), solar PV, and other energy efficiency improvements. The programme takes a whole-house approach: rather than just installing a single measure, Nest assesses what the property needs to achieve a meaningful EPC improvement.
To apply or to check eligibility, call the Nest helpline on 0808 808 2244 (free phone, Monday to Friday, 9am to 5pm). You can also apply online at nestwales.org.uk. The application includes a home survey carried out by an approved assessor at no cost to you.
Welsh homeowners on low incomes or qualifying benefits should always call Nest before exploring other routes. The scheme covers the full cost and handles all installation logistics – including the survey. If your EPC is E or below and you meet the income test, Nest is your fastest route to a free heat pump.
Northern Ireland – NISEP
Northern Ireland’s NISEP scheme offers funded heat pump installations but is frequently oversubscribed. Applications open annually – check uregni.gov.uk for the current status.
Northern Ireland operates outside the UK-wide BUS, ECO4, and Warm Homes schemes. Instead, heat pump funding in Northern Ireland is delivered through the Northern Ireland Sustainable Energy Programme (NISEP), which is regulated by the Utility Regulator (UREGNI) and funded by energy suppliers operating in Northern Ireland such as firmus energy and SSE Airtricity.
How NISEP Works
NISEP operates on an annual cycle: funding is allocated at the start of each scheme year and – given the high demand relative to available budget – often becomes unavailable well before the year ends. This means that whether you can access NISEP funding in any given year is partly a matter of timing. The scheme covers a range of energy efficiency measures including heat pumps, insulation, and heating controls. Eligibility is generally targeted at low-income households and those with health vulnerabilities, though some general-eligibility strands exist.
It is important to be honest about the current situation in Northern Ireland: compared to the rest of the UK, heat pump grant availability is more limited, less predictable, and more dependent on funding cycles. Homeowners in Northern Ireland who are not in a qualifying low-income category face fewer pathways to subsidised installation. The Renewable Heat Incentive (RHI) – which previously paid tariffs to heat pump owners in Northern Ireland – closed to new applicants in 2022.
For the most current information on available NISEP funding strands and how to apply, visit uregni.gov.uk or contact the Utility Regulator’s consumer team. You can also check with accredited installers in Northern Ireland, who will be aware of which energy supplier schemes are currently open.
Northern Ireland homeowners face the most constrained heat pump grant landscape in the UK. NISEP is the primary route but operates on an annual funding cycle and is frequently oversubscribed. Check uregni.gov.uk at the start of each calendar year for the latest availability – and register your interest early.
VAT Relief on Heat Pumps
Heat pump supply and installation is subject to 0% VAT until March 2027 for domestic properties in the UK, saving homeowners typically £500-£750 on a standard ASHP installation.
In 2022, the UK government reduced VAT on the supply and installation of energy-saving materials – including heat pumps – to 0% for domestic residential properties. This measure was originally set to run until March 2027, at which point the rate is scheduled to revert to 5%. The 0% rate applies to both the heat pump unit itself and the associated installation labour – meaning the full invoice from your MCS-certified installer should be zero-rated, provided the installation is at a domestic property and meets HMRC’s criteria for energy-saving materials.
What VAT Relief Covers
The 0% VAT rate covers: the heat pump unit, all associated pipework and refrigerant connections, the hot water cylinder (where supplied as part of the same installation), radiator upgrades carried out as part of the heat pump installation, underfloor heating installed as part of the same project, and the installation labour. Ancillary materials such as electrical upgrades or building work not directly related to the heat pump system may still attract 20% VAT – your installer should itemise their quote clearly.
On a typical air-to-water ASHP installation costing £12,000 (before the BUS grant), the 0% VAT rate saves approximately £600 compared to the standard 20% rate. When the rate reverts to 5% in March 2027, the saving compared to the old rate reduces to roughly £300 – though 5% is still lower than the pre-2022 rate of 20%. There is no application process for VAT relief – it is automatically applied by your MCS-certified installer to qualifying installations.
0% VAT is a silent saving that every homeowner getting a heat pump installed before March 2027 receives automatically – no application needed. On a typical installation it saves £500-£750. If your installer’s quote shows VAT at 5% or 20%, query it before signing.
FREE QUOTE COMPARISON
Compare Heat Pump Quotes from Trusted Suppliers
✓ £7,500 BUS grant available
£7,500 BUS grant available • MCS-certified installers • 100% free
Can You Combine Heat Pump Grants?
Yes – in some cases. The most common legal combination is BUS plus 0% VAT. BUS and ECO4 cannot be applied to the same property; Warm Homes Local Grant is a separate track from both.
One of the most common questions homeowners ask is whether they can combine multiple grants to further reduce the cost of a heat pump. The answer depends on which schemes you are eligible for. Some combinations are explicitly permitted; others are prohibited by the rules of each scheme. The table below summarises the stacking rules for the main active schemes.
| Scheme | Stack with BUS? | Stack with ECO4? | Stack with 0% VAT? | Stack with HES (Scotland)? | Notes |
|---|---|---|---|---|---|
| BUS (£7,500) | – | ✗ Prohibited | ✓ Yes | ✓ Yes (check rules) | Most households use BUS + 0% VAT together |
| ECO4 (up to 100%) | ✗ Prohibited | – | ✓ Yes | N/A | ECO4 is fully funded – BUS not needed |
| Warm Homes Local Grant | ✗ Separate track | ✗ Separate track | ✓ Yes | N/A (England only) | Own eligibility rules; does not interact with BUS/ECO4 |
| Home Energy Scotland | ✓ Yes (check rules) | N/A | ✓ Yes | – | Grant + loan elements combined carefully with BUS |
| 0% VAT | ✓ Yes | ✓ Yes | – | ✓ Yes | Automatic – no separate application |
| Nest (Wales) | N/A | N/A | ✓ Yes | N/A | Nest is fully funded; BUS not applicable |
The single most important stacking rule to understand is that BUS and ECO4 are mutually exclusive. A property can only receive support from one of these two schemes. The practical implication is that if you qualify for ECO4 (which can fund the full cost), you should use ECO4, not the BUS. If you do not qualify for ECO4 – because your income or EPC rating does not meet the criteria – then BUS is your primary route.
The Warm Homes Local Grant is deliberately designed as a separate programme from both BUS and ECO4. A household that receives a Warm Homes Local Grant for a heat pump installation has used a different funding mechanism altogether, and the interaction between schemes needs to be managed carefully by the local authority delivering the programme.
Most homeowners using the BUS will automatically benefit from 0% VAT – the most common and simplest combination. If you are in Scotland, ask Home Energy Scotland whether you can layer in the HES grant or loan alongside the BUS. Never assume two schemes can be combined without checking – the rules change and violations can require repayment.
Expired Schemes – What Is No Longer Available
Three major heat pump support schemes have closed since 2021: the Renewable Heat Incentive (2022), the Green Homes Grant (2021), and the Home Upgrade Grant Phase 2 – HUG2 (March 2025).
If you have been researching heat pump grants for a while, you may have encountered references to schemes that are no longer accepting applications. It is worth understanding what has closed to avoid wasting time on dead ends:
Renewable Heat Incentive (RHI) – closed March 2022. The RHI paid quarterly tariffs to homeowners and businesses with qualifying renewable heating systems, including heat pumps, for seven years after installation. It was replaced by the Boiler Upgrade Scheme. No new applications have been accepted since 31 March 2022, though existing RHI recipients continue to receive their tariff payments through to the end of their seven-year period.
Green Homes Grant – closed March 2021. The Green Homes Grant Voucher Scheme offered up to £10,000 for energy efficiency improvements including heat pumps. It was widely criticised for poor administration and closed prematurely after less than a year in operation, with many approved vouchers left unredeemed due to installer capacity issues. No successor scheme carries the same name.
Home Upgrade Grant Phase 2 (HUG2) – closed March 2025. HUG2 was a targeted scheme for off-gas-grid low-income households, providing fully funded measures including heat pumps and insulation. It was the predecessor to what has now evolved into the Warm Homes: Local Grant framework. HUG2 closed to new applications at the end of March 2025, and the Warm Homes Local Grant launched in April 2025 as the replacement programme.
How to Avoid Heat Pump Grant Scams
Legitimate heat pump grants are always applied for by MCS-certified installers, never require upfront payment from the homeowner, and are never sold by cold callers claiming to “process” your application for a fee.
The proliferation of heat pump grant schemes has been accompanied by a parallel growth in fraudulent operators claiming to offer grant-funded installations. Trading Standards and Citizens Advice have both published warnings, and the costs to homeowners who fall victim can run into thousands of pounds for substandard or incomplete installations. Here is what to look for.
MCS Certification: The Non-Negotiable Check
Every legitimate heat pump installer claiming grant funding must hold MCS (Microgeneration Certification Scheme) certification. MCS is an independent, government-backed certification scheme that verifies installer competency and product standards. You can check any installer’s current certification status for free at mcscertified.com – search by company name, postcode, or technology type. If an installer cannot provide their MCS certificate number or does not appear on the register, do not proceed regardless of how compelling the offer sounds.
Red Flags to Watch For
Upfront grant application fees: No government grant scheme requires homeowners to pay a fee to access or apply for grant funding. If anyone charges you for “processing your BUS application” or “securing your grant”, this is a scam. Legitimate installer applications to Ofgem are free.
Cold calls claiming you “have been pre-approved”: Government grant schemes do not cold-call households to notify them of pre-approval. If you receive an unsolicited call, text, or door-knock from someone claiming you qualify for a free heat pump “because of a government scheme”, treat this with extreme suspicion. Report it to Action Fraud (0300 123 2040) and Citizens Advice (0808 223 1133).
Pressure to decide immediately: Grant-funded installations under BUS, ECO4, and other legitimate schemes involve a proper survey, written quotation, and cooling-off period. Any installer demanding you sign or pay a deposit on the day of their visit is not operating legitimately.
TrustMark verification: For schemes including ECO4 and the Warm Homes Local Grant, the government requires installers to hold TrustMark accreditation in addition to MCS certification. You can verify TrustMark status at trustmark.org.uk. Holding both MCS and TrustMark is the standard for any reputable heat pump contractor working under government grant schemes.
Before engaging any installer for grant-funded work, spend two minutes on mcscertified.com and trustmark.org.uk to verify their credentials. These checks cost nothing and protect you from the most common forms of heat pump grant fraud. Never pay upfront to access a government grant – that is always a scam.
Summary – All UK Heat Pump Grants at a Glance
Six active heat pump grant and funding schemes are available across the UK in 2026. The right scheme depends on your region, income, and property EPC – most homeowners qualify for at least one.
The following table summarises every active UK heat pump grant scheme as at February 2026. Use this as a quick reference when deciding which scheme to apply for first, or which to investigate further based on your circumstances.
| Scheme | Region | Max Grant Value | Income Tested? | Heat Pump Types Covered | End Date |
|---|---|---|---|---|---|
| Boiler Upgrade Scheme (BUS) | England & Wales | £7,500 (ASHP/GSHP) | No | Air-to-water, ground source, air-to-air, biomass | March 2028 |
| ECO4 | England, Wales & Scotland | Up to 100% of cost | Yes (£31K / benefits) | Air-to-water, ground source | December 2026 |
| Warm Homes: Local Grant | England only | £30,000 (£15K heating + £15K insulation) | Yes (£36K / benefits) | Air-to-water, ground source | March 2028 |
| Home Energy Scotland | Scotland only | £15,000 (£7.5K grant + £7.5K loan) | No | Air-to-water, ground source | Ongoing (check HES) |
| Warmer Homes Scotland | Scotland only | Up to 100% of cost | Yes (fuel poor) | Air-to-water, ground source | Ongoing (check HES) |
| Nest (Wales) | Wales only | Up to 100% of cost | Yes (£18K-£24K / benefits) | Air-to-water, ground source | Ongoing (check nestwales.org.uk) |
| NISEP (Northern Ireland) | Northern Ireland only | Varies by strand | Yes (income & vulnerability) | Air-to-water, ground source | Annual cycle (check uregni.gov.uk) |
| 0% VAT Relief | All UK | £500-£750 (typical saving) | No | All residential heat pump types | March 2027 (then 5%) |
If you are an English homeowner who does not receive benefits and earns above £36,000, the BUS combined with 0% VAT is your most realistic route – and it is still a substantial package. If you are a lower-income household in England, start with ECO4 or Warm Homes Local Grant before looking at the BUS. In Scotland, call Home Energy Scotland first regardless of income. In Wales, Nest is the starting point for lower-income households. The right first step in every case is a free survey from an MCS-certified installer or a call to your region’s advisory service – not a third-party “grant checker” website. For city-specific grant stacking advice, see our Manchester heat pump guide.
