Sweden's air-to-air playbook: what UK installers can borrow as BUS V5 opens the £2,500 grant

The Boiler Upgrade Scheme (BUS) moved to version 5 on 28 April 2026, and for the first time UK policy recognises the heat pump technology Sweden has been quietly installing for thirty years: air-to-air. The new £2,500 grant for air-to-air systems sits alongside the £7,500 air-to-water grant - smaller cheque, much faster install, completely different operational profile, and a customer pool the UK heat pump industry has barely touched.

This isn't an argument that air-to-air is "better" than air-to-water. It's an argument that the UK market just got a second product line, and the installer who treats it the same way they treat their air-to-water work will leave money on the table. Sweden's installers have already run the experiment for us. Here's what holds up when you read across.

Sweden in one paragraph (because the comparison is the point)

Sweden has the highest heat pump penetration of any major economy. Heat pumps cover the majority of homes there, and they got there over thirty-plus years of steady installer-led adoption that began with the 1970s oil shock and accelerated through the 1990s. The technology mix is air-to-air-dominated - air-source units that move heat between outside air and inside air without a wet circuit, often configured as multi-split systems with one indoor unit per room. Air-to-water systems (the UK's near-default until V5) exist in Sweden but are not the majority. The earlier piece on what the UK can learn from Sweden's heat pump rollout covers the technology-mix story in depth - the operational story is the focus of this one.

What that thirty years of Swedish installer experience created is an operations model purpose-built for fast, no-wet-works heat pump installs. The UK is now, for the first time, in a position to borrow it.

Why air-to-air is operationally different

The substantive difference is wet versus dry. An air-to-water heat pump connects to your existing wet central heating circuit - radiators or underfloor - and produces hot water for a cylinder. That means the install has to integrate with the existing wet system (or replace large parts of it), and the design has to balance the heat pump output against the emitters and the cylinder demand. That's the work captured in the MIS 3005-D (Microgeneration Installation Standard, design) heat-loss workup, the emitter sizing, and the weather compensation strategy.

An air-to-air heat pump doesn't touch the wet circuit. It's a refrigerant circuit between an outdoor unit and one or more indoor head units, each blowing tempered air directly into a room. There's no cylinder (domestic hot water is handled separately, typically by an immersion or a separate cylinder), no radiator sizing, no underfloor coordination, no flow temperature curve. The design work is room-by-room - what's the heat loss, what's the unit capacity, where does the head go, where does the refrigerant pipework run. The unit sizing tools manufacturers provide do most of this work natively.

The downstream operational consequences:

• Install time typically lands at 1-2 days for a domestic air-to-air system vs 3-5 days for a typical air-to-water retrofit. Multi-room air-to-air systems with multiple head units can stretch to 2-3 days but rarely past that.
• Disruption to the customer is far lower. No wet circuit drained, no rooms inaccessible while emitters are changed out, no cylinder swap-out. Many installs are reasonably done with the family in residence.
• Material costs sit lower because there's no cylinder, no large emitters being changed, no buffer tank, no wet system reconfiguration. The bill is dominated by the outdoor unit, the head units, the refrigerant pipework, and the electrics.
• Refrigerant work matters more. Air-to-air systems are field-charged refrigerant circuits across multiple indoor units. F-Gas (Category I or II) qualified personnel are essential and the refrigerant audit trail is the audit risk.
• Maximum Demand calculation still matters for the Energy Networks Association heat-pump / electric-vehicle (ENA HP/EV) notification, but with smaller-rated outdoor units the new MD often stays under the 60A-per-phase threshold and the install can proceed with post-install notification rather than pre-approval.

What stays the same: MCS certification of the installer; MID (MCS Installation Database) registration within 10 working days of commissioning; BUS V5 quote/invoice paperwork showing total cost, grant deduction, and net payable; homeowner handover pack; Part L (conservation of fuel and power) and Part F (ventilation) sign-off where applicable. The compliance backbone doesn't change. The wet-works backbone disappears.

The UK industry built itself around air-to-water because the BUS only paid for air-to-water. Now BUS V5 pays for both. The installers who treat air-to-air as the same product with a smaller cheque are going to lose to the ones who treat it as a different product with a different operations model.

Who buys air-to-air

Three customer pools the UK industry has been underserving become viable under V5:

1. Properties without wet central heating. Period housing on storage heaters, electrically heated flats, off-grid rural properties where the customer doesn't want a wet retrofit. Sweden has been selling into this segment for decades; the UK has been telling these customers they're not eligible for BUS, full stop.
2. Customers who don't want construction-grade disruption. Older homeowners, families with young children, properties under part-rented occupation. Air-to-air's 1-2 day install footprint changes the customer conversation completely.
3. Properties where air-to-water doesn't make commercial sense. Smaller flats, single-bedroom properties, listed properties where wet circuit changes are restricted. The £2,500 grant on a £4,000-£6,000 install puts these in reach for the first time.

That doesn't mean the air-to-water market shrinks. It means the addressable market for "heat pumps" expands to include customers air-to-water couldn't service. For installers running 15-50 air-to-water jobs a month today, the practical question is whether the office and install team can carry a second product line without breaking what's working.

The operations model Sweden built (and what to borrow)

Three things stand out from how Swedish installers run high-throughput air-to-air operations:

1. The survey is short and standardised. Room-by-room heat loss, unit capacity selection, indoor head positioning, outdoor unit positioning, refrigerant pipework route, electrical loading. There's a standard form, the engineer walks the house in 30-45 minutes, and the design is essentially complete before they leave. Compare this to a 2-3 hour air-to-water survey covering existing wet system, emitter audit, cylinder spec, flow temperature design, weather compensation strategy.

2. The install is paired or solo, not team. Swedish air-to-air installs are typically 1-2 engineers, with one engineer doing the outdoor work and the other the indoor heads, refrigerant joints made and pressure-tested as they go. UK installers used to 3-engineer air-to-water teams should expect to redeploy headcount, not add it.

3. Commissioning is data capture, not adjustment. Once the refrigerant circuit is pressure-tested, vacuumed, and charged, the system runs at manufacturer-set parameters. There's no weather compensation curve to design or commission; the indoor heads run on room thermostats. The MCS commissioning certificate is shorter and more standardised. Mobile-app commissioning captures the F-Gas refrigerant log, the unit serial numbers, the room-by-room test data, photos, and the customer handover signature - all in one pass.

The data-flow win is the same one Payaca customers report on the air-to-water side: capture once on the mobile app, generate the MCS commissioning certificate, the MID submission data, the BUS V5 redemption pack, the homeowner handover bundle from one record. The shape of the data is different for air-to-air (room-by-room rather than wet system) but the workflow is identical.

What we hear from heat pump installers in onboarding

The air-to-air conversation is starting to surface in onboarding sessions. Eaasy Heat - a Growth-tier Payaca customer since April, heat-pump specialist - had MCS compliance and the BUS V5 grant deduction process at the centre of their first onboarding session; the V5 air-to-air eligibility wasn't the lead topic but it sat in the same paperwork pile. McInnes Group, a new heat-pump install business moving through Payaca onboarding, has the same pattern - the V5 paperwork model needs to carry both product lines, not just air-to-water.

For installers exploring the air-to-air line, the operational questions to settle before quoting the first job are:

• Which manufacturers are you going to standardise on (and which can your engineers F-Gas-certify against)?
• What does the survey form look like - and is it different enough from your air-to-water survey that you need a separate project type?
• How does the BUS V5 quote/invoice template handle the £2,500 grant level vs the £7,500 level - your customer-facing maths needs to show the right number?
• What's the commissioning certificate going to look like, and does your mobile app commissioning workflow handle room-by-room data rather than wet-system data?
• Who in the office owns the MID registration for air-to-air jobs - same admin, or do you need to grow the team?

None of these is a software problem. They're operational decisions an installer makes before the line opens. The software side - the project record, the pipeline stages, the document templates - shouldn't be the blocker.

What "V5 air-to-air ready" looks like in the next 30 days

If you're a UK heat pump installer looking to add air-to-air alongside an existing air-to-water line, the 30-day prep is short:

1. Project type or pipeline for air-to-air. Different stage configuration from air-to-water - shorter install, different commissioning, smaller grant. Keep it visually separate so the office sees the mix at a glance.
2. Survey form for room-by-room air-to-air. Heat loss per room, indoor head positioning, outdoor unit positioning, refrigerant pipework route, electrical loading. Don't reuse the wet-system survey; the data shape is different.
3. BUS V5 quote/invoice template variants. The £2,500 air-to-air grant deduction maths needs to render correctly on the same audit-ready document pattern your air-to-water quotes already use. Para 8.09 audit checks apply to both product lines.
4. F-Gas qualified personnel and refrigerant audit trail. Air-to-air is field-charged refrigerant work; the F-Gas Category I or II certification has to flow into every install record.
5. Commissioning checklist for air-to-air. Pressure test, vacuum, charge, room-by-room test, MCS commissioning certificate, MID registration. Different from air-to-water; needs its own checklist.
6. Decision on the customer-facing positioning. Are you marketing air-to-air as "low-disruption heat pump", "BUS-eligible alternative for properties without wet central heating", or both? The answer shapes the lead-gen and qualifying script.

The UK heat pump industry has been operating as a single-product business for fifteen years. BUS V5 made it a two-product business in one regulatory step. The installers who treat the second line with the operational respect Sweden's installers have given it for three decades will be the ones who grow their addressable market the most over the rest of the Warm Homes Plan window.

Sources: SI 2026/390 (BUS V5 regulations); BUS Installer Guidance V5 (Ofgem); Heat Pump Association; IEA reporting on Sweden's heat pump market (multiple years).

Related reading: Learning from Sweden's heat pump rollout | The Warm Homes Plan is delivery-constrained, not money-constrained | BUS V5 and the upfront discount | Heat pump commissioning under BUS V5 | Heat pump installer solutions