How to Run a Heat Pump Installation: From Survey to MCS Certificate

What you will learn

• How to determine G98 or G99 at survey stage - and why G99 requires written DNO approval before any electrical connection work begins.
• Why a room-by-room heat loss calculation to BS EN 12831-1:2017 matters for system sizing, MCS compliance, and protecting against performance disputes.
• How to structure a BUS quote correctly and apply for the Ofgem voucher before procurement starts - with voucher expiry tracking built into the job record.
• How to manage the cash flow gap created by the BUS grant, and why the redemption claim must be submitted on commissioning day, not days later.
• What a complete eight-step commissioning checklist covers and why it must be compiled during commissioning, not reconstructed from memory afterwards.
• How to raise the MCS certificate, register the IBG, self-certify Building Regulations, and issue the final invoice on the same day as commissioning sign-off.

A heat pump installation is more documentation-intensive than almost any other trade job. The Boiler Upgrade Scheme (BUS) requires MCS certification, a commissioning record, and a completed MCS certificate before Ofgem will reimburse the grant. G99 applications must be submitted and approved before any electrical connection work starts. Insurance Backed Guarantees must be registered before the job closes. Miss any of these steps, or complete them in the wrong order, and the £7,500 grant your customer expects to receive gets delayed - or refused.

With over 3,500 BUS applications in February 2026 alone and the scheme extended through to 2030, the volume of work is there. But the margin risk is also real. Ofgem pays the installer, not the customer. You apply the grant as an upfront discount on the invoice, then wait for Ofgem reimbursement. That is £7,500 per job sitting in your working capital gap until the claim clears. Getting the process right protects both the grant and your cash flow.

This guide covers a heat pump installation from initial survey to MCS certificate - every step, in order.

Phase 1: Pre-Installation Survey and Heat Loss Calculation

The survey is not a sales visit. It is a design appointment that produces a binding technical record. Everything that follows - the quote, the BUS application, the equipment specification, the DNO notification - depends on what you capture here.

Confirm eligibility before attending. The BUS requires the property to have an existing fossil fuel or non-heat-pump electric heating system. Confirm this by phone before booking. Properties that have already received government funding for a heat pump or biomass boiler are not eligible.

Conduct a room-by-room heat loss calculation. MCS requires this to BS EN 12831-1:2017. It determines the heat output the system must deliver at the design external temperature for your region, and therefore the correct heat pump size. An undersized unit will fail to heat the property. An oversized unit will short-cycle, reducing efficiency and increasing wear. Record floor area, ceiling height, construction type, glazing area, and insulation standard for every room.

Assess the emitters. Heat pumps work at flow temperatures of 35-50°C rather than the 70-80°C typical of gas boilers. Radiators sized for gas may be too small to deliver the required heat at lower flow temperatures. Identify any radiators that need upgrading and include the replacement cost in the quote as a named line item - not bundled into the installation price.

Determine the DNO notification route. This is one of the most operationally critical steps. Most standard and larger heat pump units require a G99 ("Apply to Connect") application to the local Distribution Network Operator before any electrical connection is made. The DNO must approve the application before you can proceed - this is not optional in 2026. Smaller, efficient units may qualify for G98 ("Connect and Notify"), where you install and then notify the DNO within 28 days. Check the specific unit's approval status with the manufacturer. If G99 applies, submit the application as soon as the contract is signed - typical processing times mean the sooner it goes in, the less likely it is to delay installation.

Assess the electrical consumer unit. Confirm there is capacity for a dedicated circuit to the heat pump. Most modern UK homes have sufficient capacity without major electrical works. If an upgrade is needed, price it separately and include it as a named line item.

Record everything in a written design document. The survey output is the design specification: heat loss figures by room, system design, equipment specified, emitter upgrades required, external unit siting notes (south-facing where possible, clearances from boundaries and obstacles, proximity of neighbouring properties for noise considerations), and electrical assessment.

Phase 2: Quote, BUS Voucher Application, and Job Setup

Structure the quote correctly for BUS jobs. Show the full installation price and deduct the BUS grant as a named line item. Do not hide the grant in the price. Ofgem requires the full grant to be applied as an upfront discount, and the customer must not be charged the discounted amount. The standard BUS grant for air source, ground source, and water source heat pumps is £7,500. From 21 July 2026 to 31 March 2027, eligible off-gas-grid properties (oil or LPG heating) can access a temporary £9,000 grant - confirm eligibility at survey.

Apply for the BUS voucher immediately on contract acceptance. You apply to Ofgem on behalf of the customer. The customer consents and provides identity verification as part of the application. BUS vouchers have a validity window - track the expiry date from the day the voucher is issued. If the installation falls outside the window, apply for an extension before it expires.

Structure the payment schedule before any procurement starts. With BUS jobs, your invoicing has two parallel tracks: the customer payment schedule and the Ofgem reimbursement claim. A typical structure on a £12,500 installation with a £7,500 BUS grant:

• Deposit (25-30% of the net-of-grant amount) on contract signature, triggering job setup and procurement
• Equipment delivery milestone invoice when the heat pump unit is delivered and counted
• Completion invoice (balance of the net-of-grant amount) on commissioning sign-off
• BUS redemption claim to Ofgem submitted on the same day as MCS certificate issuance

Create the job record before any supplier contact. Capture the billing contact, the customer's consent reference from the BUS application, and the voucher expiry date.

Phase 3: Equipment Procurement

Raise one purchase order per supplier. A typical heat pump installation involves separate orders for the heat pump unit, the hot water cylinder, radiators or underfloor heating components (if upgrading emitters), controls, and pipework and insulation materials. Each supplier needs its own purchase order with the job reference number, agreed price, and required delivery date.

Allow for heat pump unit lead times. Heat pump unit availability varies by model and manufacturer. Confirm current lead time with your supplier before committing a delivery date to the customer or the BUS voucher timeline. Get written acknowledgment of the order within five working days.

Count every item before signing the delivery note. Do not sign until you have confirmed quantities against the purchase order. Record any shortages or damage in writing to the supplier the same day, with photographs. Do not proceed with installation until a confirmed replacement date is in writing. For a BUS job with a voucher expiry date approaching, a delivery shortage that delays the install by two weeks is not just an inconvenience - it can jeopardise the grant.

Confirm F-gas certification for any refrigerant circuit work. Most modern monobloc air source heat pumps arrive pre-charged. Any work on the refrigerant circuit must be carried out by a person holding the relevant F-gas qualification. Confirm this before booking installation if any system-specific refrigerant handling is required.

Phase 4: Site Preparation and Installation

Prepare the external unit base first. The heat pump must sit on a firm, level surface capable of supporting its weight. If no suitable surface exists, lay a 150mm thick flat-trowelled concrete base or position paving slabs on compacted hardcore. The base must also minimise noise and vibration transmission to the building and the surrounding area.

Install the dedicated electrical supply before connecting the unit. This requires a dedicated circuit from the consumer unit with a correctly sized breaker, and a weatherproof lockable isolator positioned outside the building. All electrical work must be carried out by a competent person. If G99 applies, DNO approval must be confirmed in writing before making the electrical connection to the mains supply.

Complete the system flush before filling. On retrofit installations where existing pipework is being reused, the system must be thoroughly flushed and cleaned before filling with the thermal fluid. Failure to do this compromises heat pump performance and can void the manufacturer warranty.

Insulate all pipework - internal and external. Poor pipework insulation directly reduces system efficiency. Every internal and external pipe must be insulated to a suitable grade. Do not leave any section of exposed pipework on the system.

Track labour by installation phase. Record hours against the specific phase - site preparation, pipework, electrical, controls - not as a single project total. This gives you an actual-vs-estimate comparison at close and allows you to identify where the job ran over on future similar quotes.

Phase 5: Commissioning

Commissioning is not a final check - it is a structured verification process that produces the evidence required for the MCS certificate.

1. Verify water circuit pressure and flow rate. Confirm the system is correctly pressurised and that the flow regulator on the return pipe is delivering the required flow rate through the heat pump.
2. Check all pipework connections and insulation are complete and correct.
3. Programme the controls. Set the weather compensation curve, zone controls, domestic hot water schedule, and the Legionella protection pasteurisation cycle. Record all settings.
4. Carry out a functional test. Verify the heat pump runs in heating mode, achieves target flow temperature, and the controls respond correctly.
5. Test domestic hot water delivery to the cylinder. Confirm recovery time and temperature.
6. Check condensate drainage is clear and functional.
7. Complete the MCS commissioning checklist during the commissioning process, not afterwards from memory.
8. Conduct the customer handover. Walk the customer through the control interface, explain seasonal optimisation (lower flow temperature targets compensated by longer run times), emergency shutdown, and filter maintenance. This is a requirement under the Consumer Code and protects you if a performance dispute arises later.

Phase 6: MCS Certificate, Building Regulations, IBG, and Final Invoice

Everything in this phase happens on the same day as commissioning sign-off.

Raise the MCS certificate in the MCS portal. The certificate is generated from the commissioned job record. It must be submitted to the customer and is required for BUS voucher redemption. Do not delay this step - it unlocks the grant and your final invoice.

Notify for Building Regulations via your Competent Persons Scheme (CPS). As an MCS-certified installer registered with NAPIT, NICEIC, or OFTEC, you self-certify the installation under Building Regulations. Your CPS handles the notification. Capture the notification reference in the job record.

Register the Insurance Backed Guarantee (IBG). As of 2026, MCS requires you to provide a minimum 6-year warranty backed by an IBG provider. Register the IBG on commissioning day - not days or weeks later as an admin task.

Submit the BUS redemption claim to Ofgem. Attach the MCS certificate. Ofgem reimburses the installer, not the customer. Track the open redemption claim as a named receivable with the voucher reference and submission date.

Raise the final invoice on commissioning day. The final invoice should reference the MCS certificate number and include a clear breakdown: installation work, emitter upgrades, electrical work, and any other named line items from the order confirmation. Apply the BUS grant as the agreed discount and confirm the net amount payable by the customer. Sync to your accounting software the same day.

Keeping the Process Tight Across Multiple Jobs

A BUS portfolio creates administrative pressure that a single-job operation does not. You have multiple voucher expiry dates to track, multiple open Ofgem reimbursement claims to chase, and multiple MCS certificates to submit on the correct day. Each one is a cash flow event.

The disciplines that protect margin on a single heat pump job - one PO per supplier, delivery count before signing, labour tracked by phase, final invoice raised on commissioning day - are the same disciplines that keep a growing portfolio under control. Build the process around the job record: survey notes, DNO application reference, voucher details, equipment purchase orders, commissioning checklist, IBG registration, and BUS redemption reference all linked to the same job before the file closes.

• How to Become an MCS Certified Heat Pump Installer: A Complete GuideHTAA - Hampshire Training and Assessments · accessed 2026-06-11
• Boiler Upgrade Scheme explainedEnergy Saving Trust · accessed 2026-06-11
• Boiler Upgrade Scheme: Guidance for Installers (Version 5)Ofgem · accessed 2026-06-11
• Best Practices for Installing Air Source Heat PumpsGrant Engineering (UK) Ltd · accessed 2026-06-11
• Heat Pump Costs UK 2026: Price Breakdown and CalculatorUK Home Energy · accessed 2026-06-11
• Heat Pumps - MCS CertifiedMCS Certified · accessed 2026-06-11

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