A set of pages designed to help you plan your DIY heat pump or air conditioner installation.

Checkmark is based in Bromley, South East London / Kent. Our typical coverage is inside the M25 or within 20 miles of Bromley. See ‘what we do’.

Whether you use our services or not (and we hope you decide to!), the aim of these information pages is to offer some insight and to help you decide if you want to install your own air conditioner / air source heat-pump (ASHP).

What is the difference between air-con and an ASHP?

The answer is - not very much. Both take latent heat from the air and move it somewhere else.

‘Heat-pump’ often refers to a system which creates and circulates hot water around a central heating system. Modern air conditioners have indoor units that can blow warm or cool air into a room, but don’t usually heat water. People associate cooling with air-conditioning, but the reality is ‘conditioning’ actually includes cooling, heating and dehumidification. However, the distinctions are often blurred.

Can I DIY an install?

You can do most of an install yourself. But by law you can’t touch the refrigerant gas connections - and that’s where Checkmark can help. You do the preparation and we can connect, test, commission and certify your install. Also see working with F-gas.

Home DIY installers usually choose to install a mini-split air conditioner. A ‘mini-split’ consists of separate indoor and outdoor units, joined by refrigerant pipes.

Why a ‘mini-split’ air conditioner?

Modern mini-split units are efficient and can provide both heating and cooling to a room. With their compact, discreet indoor units, they are ideal for a home or garden offices, living spaces or even a workshop.

These information pages focus on installing a ‘mini-split’ air conditioner. However, much of the information given here is applicable to other systems like air source heat-pumps and multi-room split systems too.

Will I save money on my heating bills?

The efficiency of air-source heat-pumps / air conditioners depends on the unit and on the outside temperature. Above around 3°C most units offer efficiencies of between 3:1 and 5:1. This means for every kW of electricity put in you get between 3 and 5 kW of heat out. Below 3°C, the efficiency reduces - the exact reduction depend on the model.

The UK has a lot of days when it’s single digit temperatures and ‘a bit miserable’. But that’s when these units perform well!

We’re increasingly seeing some very hot and uncomfortable summer days too, and the cooling that these units offer is vastly superior to a portable air conditioner. They can provide a welcome respite from the heat.

Daikin’s UK website has a page that explains more about efficiency measurement Opens in a new window.

Will I save money by doing a DIY install?

Yes. Checkmark isn’t trying to compete with companies offering a full (non-DIY) install. Instead, we want to help competent DIYers install systems, save money, and gain the satisfaction of doing a good job. Going DIY will save most people around a £1000 for a comparable installation.

Is DIY installation difficult?

If you are a seasoned DIYer, you shouldn’t find it difficult. These information pages are comprehensive - we hope you find them useful.

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Need to know

Safety and legal information you must know before you start a DIY heat pump or air conditioner install.

Plan and prepare your DIY install

Planning and preparing your own DIY air source heat pump or air conditioner install.


Things to consider during installation.

The Checkmark service

Connect, test, commission, certify - the installation steps that must be done by a qualified F-gas professional.

Frequently Asked Questions