Your home must meet the following criteria in order to for you to be able to install an air source heat pump. In most cases it's relatively easy to fulfil these criteria, but there are some challenging cases as we have flagged below. If we have included a heat pump in your pathway, it means we think a heat pump is a good option for your home, but the following criteria may require further evaluation.
Sufficient space for the outdoor unit
An air source heat pump always has an outdoor unit that collects heat from outdoor air. You need enough space for this outdoor unit. There are various regulations that govern where you can put a heat pump. It cannot be mounted on a wall facing a highway and in Wales it currently must be more than 3m from a boundary, which makes installation difficult for many terraced houses. In England, that distance is only 1m.
Sufficient space for a hot water cylinder
A heat pump needs a hot water cylinder in order to provide hot water. If you currently have a combi boiler then you will not usually have a hot water cylinder. Combi boilers do not require a hot water cylinder because they are extremely powerful and can instantaneously heat up your water when you need it. A heat pump can't provide heat that fast, and so it needs to gradually heat up water and store it for when you need it. Common locations to add a hot water cylinder include an airing cupboard, utility room or a room in the loft if it is suitably insulated. If vertical space is a challenge, then a horizontal cylinder can be used. In cases where there is no room for a cylinder, smaller thermal stores can be used. They do slightly reduce the heat pump's efficiency but enable heat pump installations in homes where they wouldn't fit otherwise.
If you already have a cylinder then that's great. It may even be possible to re-use your existing cylinder with an external plate heat exchanger to save the cost of a new cylinder.
Adequately sized radiators and pipes
Heat pumps work most efficiently at low flow temperatures. The more efficiently your heat pump runs, the less you will spend on your bills. In order for a heat pump to provide your home with enough heat while running at a low flow temperature, your radiators and pipes need to be big enough.
It is likely that your existing fossil fuel heating system runs at a relatively high flow temperature and so your radiators and pipes may be too small to heat your home at a lower temperature. This isn't always the case - sometimes the radiators have been oversized for your old system, or your home could have been improved since the radiators where installed meaning that some, or all of your existing system could be perfect for a heat pump. If your current heating system only has to run for a few hours on even the coldest days, or if it can heat your house adequately with the flow temperature set at 50 C, then your radiators may be sufficient for a heat pump already. If your radiators are too small however, you have two options:
- You can either add radiator area by installing bigger (taller, wider or simply deeper) radiators or more radiators,
- and/or you can improve your homes insulation so that your home doesn't need so much heat and hence your existing radiators are sufficient.
The systems that transfer the heat into the air in your home are called 'emitters'. While radiators are the most common in the UK, there are alternative options that also work with heat pumps, such as underfloor heating and fan coil units.
It's also possible to heat a home with small radiators and a heat pump running at a high flow temperature. The issue is that your heat pump efficiency will be lower, and your bills will be higher than they could be if you had bigger radiators.
Enough space on your electricity panel
If you don't already have a 100A fuse you will need to ask your network operator for an upgrade before starting any work. It is very unlikely that you will require a three phase connection for a heat pump!
(Sometimes) space for a buffer tank
In some cases you may want to install a buffer tank on your heat pump to store extra heat. Adding a buffer tank improves the flexibility of your heating system such that you can run your heat pump when electricity is cheap and then use the heat later. Buffer tanks are not always required and will inevitably lose some heat and so reduce the overall efficiency of your heating system. Not having space for a buffer tank definitely isn't a deal breaker!