What Are the Disadvantages of a Heat Pump? An Installer's Honest List

The short answer

A heat pump's real drawbacks are emitter sizing, upfront cost, a different way of running, and the siting of the outdoor unit. Those are design and expectation problems, and all four are knowable before you sign anything. What they are not is the two claims that dominate the internet: that heat pumps do not work in cold weather, or that they cannot heat an older house.

1. Your radiators may be too small

This is the one that causes most disappointment. A boiler sends water to your radiators at roughly 65-75°C; a heat pump is at its most efficient around 35-45°C. The same radiator emits far less heat at the lower temperature, so some rooms need larger emitters — or underfloor heating — to hold temperature on a cold day. The room-by-room heat loss calculation tells you exactly which ones, and a quote without that calculation is a guess. If a quote is unusually cheap, this is usually where the difference is hiding.

2. Higher upfront cost

Even after the grant, a heat pump costs more than swapping a boiler for a boiler. In Cornwall a typical air source installation is £11,500-£16,800 before grant; the Boiler Upgrade Scheme takes off £7,500, or £9,000 until March 2027 where you are replacing oil or LPG and have no mains gas connection. Ground source is £18,000-£32,000 before the same grant. The return comes from what you stop buying — oil, LPG or peak-rate electricity — which is why the case is strongest off the gas grid and weakest against cheap mains gas.

3. It runs low and slow

A heat pump is designed to hold a house at temperature, not to blast heat for two hours twice a day. Households used to firing a boiler morning and evening often fight the system for the first winter — deep setbacks, then a cold house that cannot recover in time. Weather compensation and long, low run times are the answer, and they are a habit change as much as a control setting.

4. The outdoor unit is visible and audible

Modern units are quiet, not silent. Permitted development requires compliance with the MCS 020 a) planning standard, which caps predicted noise at 37.0 dB(A) at the assessment position one metre outside a neighbouring habitable room window or door. In a tight terrace that calculation, not the paperwork, usually decides which part of the yard the unit can occupy. Ground source avoids the question entirely because there is no outdoor unit, at the cost of groundworks.

5. A leaky home stays expensive

The insulation precondition was removed from the Boiler Upgrade Scheme in May 2024, and the valid-EPC requirement in April 2026 — so nothing stops you installing a heat pump in a poorly insulated house. Physics is less accommodating: the higher the heat demand, the larger the unit, the higher the flow temperature and the worse the running cost. Loft insulation and draught-proofing are still the cheapest kilowatt-hours you will ever buy.

6. Planning, if you are listed or in a conservation area

Since 29 May 2025 most air source installations on houses are permitted development under Class G of Part 14 of the GPDO. The exceptions bite in Cornwall: no Class G rights on a listed building or in its curtilage, and in a conservation area or the Cornwall and West Devon Mining Landscape World Heritage Site the unit cannot go on a wall or roof fronting a highway, or nearer a highway than the house. That is a real constraint on a street-facing terrace, and it is worth resolving before a survey, not after.

Where we say no

• No workable position for the outdoor unit that passes the noise assessment — usually a mid-terrace with a shared light well and no rear access.
• A property being sold within a year or two, where the disruption will not be recovered.
• Emitter replacement the household will not accept — if the honest radiator schedule is unacceptable, the system will underperform and everyone will be unhappy.
• Cheap mains gas plus a young boiler: the sums rarely work yet, and saying so is part of the job.

What the drawbacks are not

Two myths worth retiring. Heat pumps do work in cold weather — they are the standard heating system in countries far colder than Cornwall, and our mild maritime winters are among the easiest conditions in the UK for one. And older houses are not excluded: solid-wall Cornish cottages work when the heat loss is measured and the emitters are sized for the result, which is exactly what the survey is for.

If you want the local version of all of this — grant bands, costs by property size, planning and the coverage map — see heat pumps Cornwall, or the Boiler Upgrade Scheme in Cornwall for eligibility in full. Where land allows, ground source heat pumps Cornwall removes the outdoor-unit question entirely.