By James Stalker, MCS-accredited heat pump installer and freelance NAPIT assessor, Exmouth, Devon
Nobody has ever asked me about kilowatts on a first visit. They ask what the thing will look like sitting against a stone wall, whether the radiators will suddenly be twice the size, and whether the boiler cupboard is about to become someone’s least favourite room. Fair questions. Here’s what an oil-to-heat-pump conversion genuinely does to a period house, inside and out, with real jobs and real numbers rather than brochure claims.
The unit outside
The outdoor unit is roughly the size of a large chest freezer stood on end, and it needs a bit of clearance for airflow and access. On a stone-built terraced house in Street, Somerset, we sited it against a side return where the old oil tank used to sit, so the property lost almost no ground to heating equipment. The bigger design decision is usually the base it sits on. On a period property in Newton Abbot with an uneven driveway, we built a bespoke concrete base with an integrated soakaway rather than forcing the unit onto ground that wasn’t level, which is the kind of detail that either gets done properly or looks bolted on for the next twenty years.
Noise worries people more than it should. We run a sound calculation on every installation, an MCS requirement, specifically to check neighbours won’t be affected. Stand next to a running unit and you’ll hear it. Stand where you’d normally be, in the garden or a neighbouring window, and you generally won’t.
Inside: radiators, not a museum piece
The homeowner in Street had already had three separate opinions before calling us. One wanted to fit a 16kW system. Another told them to forget the idea entirely. A proper room-by-room heat loss survey showed both were wrong. The house needed a smaller, correctly sized unit, and only the radiators that the calculations actually flagged got upgraded. That’s the pattern I see repeatedly: an oil boiler runs radiators at 70 to 80 degrees, a heat pump runs them nearer 45 to 50, so a handful of radiators need to be bigger to put out the same heat at a lower temperature. Not the whole house, just the ones the sums point to.
On a heavier job, a period property in Newton Abbot that had been running on a twenty-year-old Aga-style back boiler, the answer was different: the existing pipework was undersized throughout, so we repiped the whole hydronic system and fitted fourteen new radiators, including rooms that had never had heating at all. That’s not a like-for-like swap, it’s a proper redesign, and it shows in the finish: even heat through rooms that used to be genuinely cold, rather than one roasting radiator trying to do the whole floor’s job. I’ve set out what a Devon oil conversion costs house by house if you want to see how jobs like these get priced.
The cylinder, and the space you get back
Every heat pump needs its own hot water cylinder. On that same Newton Abbot job, relocating the cylinder freed up enough space inside the house for the homeowners to go ahead with a bathroom extension they’d been planning. It’s a detail that has nothing to do with heating efficiency and everything to do with how the finished room actually looks and works, and it’s the kind of thing worth asking about before you assume the airing cupboard is fixed in place forever.
What it costs, and what changes now
For a straightforward oil conversion, a job like this typically lands around £15,000 before any grant comes off. The Boiler Upgrade Scheme then takes £7,500 off that. What’s changed recently is that homes coming off oil or LPG now qualify for an extra £1,500 uplift on top, taking it to £9,000, and it runs to March 2027.
A failed boiler concentrates minds faster than anything. A customer in Zeal Monachorum, Crediton, had their oil boiler die completely, no heating or hot water, and assumed a heat pump would mean months of delay. We had it surveyed within a week, the grant voucher arranged, and an 8kW system commissioned just over three weeks after the first phone call, with the external pipework properly insulated in trunking rather than left exposed. The finished cost came in close to what a straight oil boiler replacement would have, once the grant was applied. The extra £1,500 for oil and LPG homes has its own timing rules, which are worth reading before you book a survey.
The obstacle in a period house is never the walls. It’s the survey nobody did, and the radiators somebody guessed at.
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