Residential · Air-to-Water
Air source heat pumps (Air-to-Water) — frequently asked questions
Straight answers to the questions we hear most from homeowners considering an Air-to-Water heat pump as a boiler replacement. For anything specific to your home, ask Current — our AI adviser can talk through the right setup for your property.
Is this the right technology?
- Is Air-to-Water the same thing as Air-to-Air?
- No — they're genuinely different technologies that solve different problems. Air-to-Water extracts heat from outside air and transfers it into your home's water-based heating system — radiators or underfloor heating — and can also heat your domestic hot water via a cylinder. It's the direct, like-for-like replacement for a gas or oil boiler. Air-to-Air heats and cools room air directly through indoor units, with no water circuit and, in almost all cases, no domestic hot water at all. If you're replacing a boiler that currently handles both space heating and hot water, Air-to-Water is the equivalent system.
- Do I need to replace my radiators?
- Possibly, and it's worth planning for rather than being surprised by. Heat pumps run most efficiently producing water at lower temperatures than a gas boiler does, which generally means larger radiators than you currently have, or well-designed underfloor heating, to release the same heat into a room at a lower water temperature. A straight swap with no radiator changes can leave a home under-heated on the coldest days — this should be part of the design conversation from the start, not an afterthought.
- Does my home need to be well insulated first?
- Not as a hard requirement — heat pumps work in less insulated homes too — but insulation matters more here than with a gas boiler. Because heat pumps run more efficiently at lower flow temperatures, a well-insulated home gets more benefit, faster payback, and needs less radiator upsizing. Worth an honest conversation about your home's insulation as part of sizing the system, rather than assuming it doesn't matter.
- Why does my hot water sometimes run hotter than usual?
- That's normal, not a fault. A heat pump heats water to a lower default temperature than a gas boiler typically does, so most systems run a periodic higher-temperature cycle (sometimes called a "legionella cycle") to maintain hygiene standards in the cylinder. It's an expected, scheduled part of how the system operates.
Efficiency & running costs
- What do COP and SCOP actually mean?
- COP (Coefficient of Performance) is a snapshot efficiency figure — how many units of heat the system produces per unit of electricity, at one specific outdoor temperature. A COP of 3 means 1kWh of electricity in produces roughly 3kWh of heat out. SCOP (Seasonal Coefficient of Performance) is the more useful, real-world figure — average efficiency across an entire heating season, across the full range of outdoor temperatures the system actually experiences. When comparing systems, SCOP is the more honest number, since COP alone can be measured under generous test conditions that don't reflect a typical UK winter.
- Is a heat pump actually cheaper to run than gas?
- It depends on the SCOP your system achieves and the price gap between electricity and gas per unit at the time — both matter, not just the heat pump's efficiency in isolation. A higher SCOP means more heat for the same electricity spend, but the comparison to gas is genuinely tariff-dependent, so it's worth working through actual numbers for your home rather than relying on a generic claim either way.
Noise & planning
- How loud is the outdoor unit, and will it bother my neighbours?
- Most modern units are considerably quieter than older reputations suggest, but it's a fair and specific question to ask, not an unreasonable one. UK installations are assessed under MCS 020, a standard that calculates a permitted noise level at the boundary of neighbouring properties, based on the unit's sound power rating and its distance from that boundary. A proper installer runs this calculation as a normal part of the design — placement (distance from bedroom windows, boundaries, and even the surface the unit sits near) affects real-world noise as much as the unit's rated output does.
- Will I need planning permission?
- Usually not. Most home heat pump installations fall under Permitted Development rights in England, provided the outdoor unit's size and its distance from a boundary meet standard conditions. You're more likely to need permission for listed buildings, conservation areas, flats and maisonettes (which generally have narrower permitted development rights than houses), or installations that don't meet the standard size/distance conditions. A proper installer should flag this during an initial assessment, not leave you to find out later.
Funding: the Boiler Upgrade Scheme
- How much is the government grant worth for Air-to-Water?
- £7,500 towards an Air-to-Water (or ground/water source) heat pump under the Boiler Upgrade Scheme (BUS). A temporary uplift to £9,000 applies to off-gas-grid homes currently on oil or LPG, for applications from 21 July 2026 through 31 March 2027. The scheme has been extended through to 2030. Grant amounts and eligibility have changed more than once in 2026, so always confirm the current figure before relying on it.
- Do I have to apply for the grant myself?
- No. The grant isn't paid to you directly — it's claimed by your MCS-certified installer and deducted upfront from your quote, so the price you're shown already reflects the discount. You don't need to apply to Ofgem yourself.
- Am I eligible?
- Broadly: your property needs to be in England or Wales (Scotland and Northern Ireland run separate schemes), currently heated by a fossil fuel or electric resistance heating, and the heat pump needs to fully replace your existing system — a hybrid setup that keeps a gas boiler as the primary heat source generally doesn't qualify. New-build properties are covered separately under the Future Homes Standard rather than this scheme. A previous requirement for a valid EPC with no outstanding insulation recommendations has also been relaxed, removing a barrier that used to exclude some homes.
- What does it actually cost me after the grant?
- Often meaningfully closer to the cost of a premium gas boiler replacement than the pre-grant headline figure suggests, once the grant and the reduced VAT rate on qualifying installations are both applied. It's worth working through the actual net number on a specific quote rather than judging affordability from the sticker price alone.
Certification & who does the work
- What does MCS certification actually protect me from?
- MCS certification of both the product and the installer is what makes a system eligible for the Boiler Upgrade Scheme grant, and it generally signals adherence to proper design practice — heat-loss calculation, correct sizing, noise assessment — rather than a generic installation. It's worth confirming before booking, not after.
- Does my installer need to be Gas Safe registered?
- Not for the heat pump installation itself — there's no gas involved. But if a gas boiler and its pipework are being removed as part of the same job, that removal work does require a Gas Safe registered engineer. Separately, the refrigerant in the heat pump's own circuit is regulated under F-Gas rules and requires an F-Gas qualified engineer to handle correctly. Worth confirming your installer holds both relevant qualifications where applicable — one doesn't automatically cover the other.
What a proper quote should include
- What should a trustworthy quote actually walk me through?
- A room-by-room or whole-home heat-loss calculation, not a generic size based on square footage alone. Whether your existing radiators are adequate at heat-pump flow temperatures, or need upsizing, and specifically where. Outdoor unit placement, factoring in noise and any planning constraints. Realistic SCOP-based running cost estimates for your specific system and usage, not a generic marketing figure. And confirmation of your Boiler Upgrade Scheme eligibility and the actual net cost after grant. A quote built around a single headline price, without this, is missing the design work that determines whether the system will actually perform well in your home.
Still have a question specific to your home? Ask Current — it can walk through radiator sizing, grant eligibility, and the right system for your property.