Air Source Heat Pump Disadvantages

The disadvantages, in brief

1. The outdoor unit needs a suitable position

A narrow passageway between houses often rules itself out. The heat pump needs room to move air, space for servicing and a sensible route back to the heating system. The airflow requirements are there for a reason, even if it's inconvenient.

I check the particular model's clearances. There isn't one distance that applies to every heat pump, and fitting the cabinet into a gap doesn't mean the position works.

Noise can rule out a position

I've ruled out proposed locations near a neighbour's window after doing the sound calculation. That hasn't necessarily stopped the installation. We've looked for a better position.

Modern units are much quieter, and customers are often pleasantly surprised when they hear one. I encourage people to listen to a working installation. They make a noise, but that doesn't necessarily make them noisy. My heat-pump noise guide explains the difference.

A quiet model still needs proper siting. Putting it somewhere awkward and promising nobody will hear it isn't a design.

2. Replacing a combi means planning hot-water storage

A combi heats water as you use it. A conventional heat-pump installation heats stored water, so I need somewhere for that storage to go. In a small terrace, this can be the hardest part of the survey.

I've fitted Mini Stores where the boiler used to be and under a utility-room worktop. We've also used purpose-built insulated external cylinder cupboards. I usually find an option, but I can't promise every property has a practical one.

These aren't interchangeable boxes. I need to match the storage and reheating arrangement to your baths, showers and household routine. A compact option that fits beautifully but doesn't meet your hot-water demand isn't the right choice.

Energy Saving Trust's heat-pump guide also identifies hot-water storage as a key change from a combi. My heat-pump hot-water guide covers the options I use.

3. Installation is more involved than a boiler swap

Our heat-pump installations normally take three to four days. A straightforward boiler replacement can often be completed in one. Converting from a combi generally adds more work because we're introducing hot-water storage as well.

There can be new pipe routes, electrical work and radiator changes. Long pipe runs add time and cost. Ask which rooms we'll need access to and what needs lifting or drilling. Hot water is normally back on the same day, ready for the evening. Heating is normally off for one or two nights.

Radiator changes should have a reason

You might need several radiators changing, one or two, or none. I calculate what each room needs and check the radiator output at the proposed flow temperature: the temperature of the water going to the radiators.

I want the quotation to explain which radiators need changing and why. You shouldn't have to accept a houseful of replacements simply because someone has said “heat pumps need bigger radiators”.

Our heat-pump installation guide takes you through the work from survey to handover.

4. You need to allow more time for heating

Lower flow temperatures are more efficient, but a system designed to run steadily at those temperatures has less spare output for a sudden warm-up. Often the adjustment is simple: start the heating earlier instead of expecting a short, very hot burst.

In colder weather, I generally advise steadier temperatures and a smaller setback, often around 2°C below the comfort setting. I agree that with the customer for their home. It isn't an instruction to heat every empty house at the same temperature all day.

I ask when you're home, which rooms you use and how quickly the property loses heat. Energy Saving Trust's operating guidance explains why flow temperature and allowing enough heating time matter.

If you've always had a combi, a hot-water schedule is new too. We plan cylinder reheating around when you need water, rather than waiting for the shower to provide feedback.

Heating just one small room needs thought

If you work from home and only want to heat a small office, tell me. A heat pump has a minimum output and needs enough water moving through it. I've used larger volumisers, which hold extra heating-system water, to manage small zones. They need space too.

Not every installation needs one. Your routine isn't automatically a reason to reject a heat pump, but it has to be part of the design.

5. Servicing and repairs need specialist knowledge

Heat-pump servicing costs more than a straightforward gas-boiler service in our business. Finding someone who can diagnose a fault can also be harder. I would ask about both before choosing an installer, not just who is available to fit it.

Manufacturer backup matters to me. I've had good experiences getting Vaillant and Bosch support around Lincoln. That is my experience, not a promised response time for every breakdown.

• Servicing: who will do it, what does it cover and what does it cost?
• Repairs: does your installer diagnose faults, and how is manufacturer support arranged?
• Backup: what will provide heating or hot water while a fault is being resolved?

Where the cylinder has an immersion heater, we check that it works and replace a failed one when needed. That gives hot-water backup, not central heating. We can also lend temporary heaters when needed.

Don't assume every compact hot-water option has an immersion heater. Ask what backup your particular installation includes, and keep to its servicing and warranty requirements.

6. Lower fuel costs aren't the whole calculation

In my experience, our systems generally cost less in fuel than gas. That doesn't mean I can promise the same saving to every household, or ignore servicing and the cost of changing the system.

Removing gas completely can remove its standing charge. Keeping a gas hob or fire can mean that charge stays. Compare the full annual cost, using your tariff and a realistic estimate of system performance. I've set out the workings in our heat-pump running-cost comparison.

A small bill leaves less money to save. If your heating costs £600 a year, an illustrative 20% reduction is £120 a year. That isn't a saving forecast. It shows why I wouldn't talk only in percentages when asking someone to give up cupboard space and change a working system.

The upfront quote also needs to include the cylinder, radiator work, pipe routes and electrics it actually requires. Any grant or tax treatment must be confirmed for the job, not assumed from an old headline.

7. Sometimes the compromise isn't worth it

I would be cautious about a high-heat-loss home with no space for larger radiators, decorative radiators the owner wants to keep, or building restrictions that prevent the changes we need.

If the design still needs 70–80°C water to keep the rooms warm, I wouldn't recommend an all-heat-pump approach. Some equipment can reach those temperatures; that doesn't make it the system I'd choose for efficient everyday heating. A hybrid system may be worth assessing instead.

An old house isn't automatically unsuitable. I look at practical insulation and draught improvements alongside the heating design. We don't need new-build insulation levels, and I won't prescribe a complete renovation by default.

The RICS consumer guide makes a useful distinction: considering the whole building doesn't mean doing every improvement at once. Any work needs to suit the building and preserve necessary ventilation.