Switching From Oil to an Air Source Heat Pump: What Off-Grid Homeowners Need to Know

Switching from oil to an air source heat pump is one of the most common renewable upgrades we carry out for homes across rural Dorset and Wiltshire that have never had mains gas. With oil prices unpredictable year to year and the government’s Boiler Upgrade Scheme currently offering extra support for off-grid properties, more homeowners are asking us what the switch actually involves day to day, beyond the grant itself.

In Brief

Switching from an oil boiler to an air source heat pump means removing the old boiler and tank and adding an outdoor unit, a heat pump compatible hot water cylinder, and sometimes larger radiators to suit the system’s lower running temperature. Off-grid homes making the switch are currently eligible for a £9,000 government grant, running until 31 March 2027.

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This guide covers exactly that. If you want the full detail on grant eligibility, we’ve covered that separately in our guide to the £9,000 grant. Here, we’re focusing on what changes in your home when you move from an oil boiler to an air source heat pump.

Why an oil to air source switch is a bit different

If you’re on mains gas, switching to a heat pump usually means disconnecting from the gas network. Off-grid homes skip that step entirely, since there was never a gas connection to remove. In some ways, that makes oil heated homes some of the best candidates for a heat pump.

What you do need to plan for is everything that comes with an oil system: the tank, the boiler itself, and often pipework and a heating system that were designed around a boiler running at a much higher temperature. None of this is a barrier to switching, it’s just part of the job, and it’s exactly the situation the government’s current £9,000 grant uplift for off-grid oil and LPG properties is aimed at.

What actually changes when you switch

A heat loss survey first. Before anything is fitted, we calculate how much heat your home loses through walls, windows, floors and doors. This tells us what size heat pump you need, and whether any other changes will help the system run efficiently.

Radiators, or underfloor heating. Heat pumps run at a lower flow temperature than an oil boiler, so they work best with a larger heating surface. That sometimes means upsizing radiators, and if you’ve already got underfloor heating in part of the house, that’s ideal. Your existing radiators aren’t necessarily too small, we’ll check as part of the survey rather than assume.

A heat pump compatible hot water cylinder. Most oil fired homes already have a cylinder, but it will usually need replacing with one designed to work with a heat pump, often a bit larger to make the most of longer, steadier heating cycles.

The old boiler and oil tank removed. Once the new system is in and commissioned, we decommission the boiler and take away the oil tank, which frees up useful space outside, often exactly where the new outdoor unit can go.

An outdoor unit. This needs roughly a 2m by 2m space outside the house. It runs quietly, but we’ll always plan the position carefully, particularly if you’re close to a neighbouring property.

What about running costs?

Oil prices swing about more than most homeowners would like, and a heat pump takes that volatility out of the equation. Air source heat pumps typically deliver three to four units of heat for every unit of electricity used, which is a big efficiency jump over any boiler burning fuel directly. We’ve broken the full cost picture down, including typical installation and running costs, in our air source heat pump cost guide, so we won’t repeat all of it here.

The £9,000 grant, in brief

From 21 July 2026 to 31 March 2027, eligible off-grid homes replacing an oil or LPG system can claim an increased Boiler Upgrade Scheme grant of £9,000, up from the standard £7,500. As of April 2026, you no longer need a fresh EPC to apply if yours has lapsed, alternative evidence such as a recent utility bill can be used instead. The Energy Saving Trust’s guide to the scheme is a good independent overview if you’d like to read more, and for the full eligibility criteria, including who doesn’t qualify, our guide to the £9,000 grant covers it in detail.

Only MCS certified installers can apply for the grant on your behalf, so it’s worth checking that whoever you get a quote from holds current MCS certification.

What installation week looks like

Most air source heat pump installations take between two and five working days, depending on the scope of work. We’ve written a full day by day breakdown in our air source heat pump installation process guide, but in short: the outdoor unit and any groundwork happen early on, the indoor components (cylinder, wiring, pipework) follow, and we test everything thoroughly before handing over.

A real example

We recently completed a project in Gillingham where an ageing oil boiler was decommissioned as part of a full renewable upgrade, replaced with a 12kW Grant Aerona air source heat pump alongside solar panels and battery storage. It’s a good illustration of how a single visit can deal with the oil system, the heating, and future energy costs all at once, though plenty of homeowners choose to switch the heating on its own first and add solar later.

We’ve also worked on older, period properties nearby, including a Victorian cottage where the owner was understandably particular about getting the details right. Age and character aren’t a barrier to a heat pump working well, though older homes do sometimes need a closer look at insulation and radiator sizing as part of the survey.

A few questions we’re asked often

Can I keep my oil boiler running as a backup?
No, not if you’re claiming the Boiler Upgrade Scheme grant. The heat pump needs to fully replace your existing fossil fuel system, rather than sit alongside it.

What happens to my oil tank?
It’s removed as part of the installation, once the new system is up and running. Most homeowners are glad to have the space back.

Is my rural, off-grid home actually a good candidate?
Often, yes. Off-grid properties are exactly who the current £9,000 uplift is designed to help, and many already have the outside space an air source heat pump needs.

Do I still need a valid EPC to apply?
Not necessarily. As of April 2026, alternative evidence such as a recent utility bill or photos of your existing heating system can be used if your EPC has lapsed.

Thinking about making the switch?

If you’re heating your home with oil and want to know whether a heat pump makes sense for your property, we offer a free, no obligation site visit and quote. Get in touch and we’ll talk you through what a switch would actually look like for your home.