Replacing a boiler with a heat pump in Hertfordshire

Is swapping a boiler for a heat pump a straight swap?

Not quite. A boiler heats water to a high temperature in a small, wall-mounted box. A heat pump heats it more gently, using an outdoor unit and a cylinder, so the change reaches your radiators, your hot water storage and your electrics. The old boiler is the easy part to remove. Planning what replaces it takes more care.

Many people replace a boiler at the point it fails or ages, but a heat pump can also be planned ahead of that, which leaves time for a proper survey and for any insulation or radiator work to be done first.

Where do I start?

With a heat loss survey, which is a room-by-room calculation of how much heat your home loses on a cold day. It tells the installer how big the heat pump should be and which radiators need to change. If a quote arrives without one, ask why.

The survey also tells you what is not worth doing. Sometimes the best advice is to improve loft insulation, draught-proof or fit better controls first, so the pump can be smaller.

What happens to my old boiler and gas supply?

For a gas boiler, taking it out means disconnecting and capping the gas supply, and that is restricted to engineers on the Gas Safe Register. A heat pump installer may do this themselves if they hold the registration, or use a separate Gas Safe engineer. Ask who is responsible for it and for the meter.

LPG falls under the same gas safety rules, so disconnecting an LPG boiler is also work for a Gas Safe registered engineer qualified for LPG. An oil boiler is a different trade, so ask who will decommission it. A redundant oil tank or LPG bottles or tank need removing safely, and if your LPG supplier owns them, ask the supplier about collection. Say which fuel you use when you enquire.

What if I have a combi boiler?

A combination boiler makes hot water on demand, so there is probably no tank. Most heat pump systems store hot water in a cylinder, which needs floor space and a place near the pipework. An airing cupboard, a utility room or a loft can work. Ask what size cylinder is proposed and how it will be fitted and certified. Unvented cylinders fall under Building Regulations.

Without a cylinder, the choice is limited. Ask the installer what they would do in a home with no room for one.

Will my radiators and pipework cope?

Heat pump radiators run cooler than boiler radiators, so they often need to be bigger to give the same warmth. Your survey should say, room by room, which radiators can stay, which need replacing, and where underfloor heating might be a better answer. Old pipework can be too narrow, and the installer may propose new runs.

A system that has had a boiler for years can also hold sludge. Expect a conversation about cleaning or flushing it.

Is my property allowed to have an outdoor unit?

Permitted development rules in England allow many houses to have an air source heat pump without a planning application, but only if a list of conditions is met, and the rules have changed in recent years. Flats and conservation areas need extra checking. A listed building has no permitted development rights for a heat pump, so it needs a planning application and usually listed building consent. Ask the installer to check your position against the current rules, and speak to your council if there is any doubt.

What can I claim help for?

The Boiler Upgrade Scheme offers a government grant towards replacing a fossil fuel heating system with a heat pump in some homes. It requires an MCS certified installer, who applies for the grant on your behalf. We do not quote figures, because the scheme and its eligibility rules change. Check the current scheme on gov.uk, and ask the installer how it applies to your home.

What about disruption?

Installing a heat pump usually takes longer than fitting a boiler, because pipes, a cylinder and an outdoor unit all need attention. Ask how long the installer expects the work to take, whether you will be without heat or hot water at any point, and how they will protect floors and furniture.

What should I include when I enquire?

• the fuel you use now: mains gas, oil, LPG or electricity
• the make and age of the boiler, if you know them
• whether you have a hot water tank, and where it is
• the type of home, roughly when it was built, and any insulation work done
• whether the property is listed or in a conservation area