“Our oil boiler was standing here, in the middle of the kitchen”, says Maria, who lives in a village near Deddington.

“It was about 30 years old, not efficient and leaking. We mopped the floor several times a day. We knew we had to replace it.”

At first, she and her husband Tim looked at a new oil boiler. “But, honestly, I couldn’t find it in my heart to burn more oil,” explained Maria, who citing her concern about climate change.

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It was not an acceptable choice for her husband either: “Modern, condensing boilers are very complicated. You cannot buy a simple one anymore, those days are gone, and I didn’t want to have a thing more complicated than it needs to be.”

After some research they found out about air source heat pump technology, which is subsidised by the government. They asked for quotes and it turned out that the cost of installing and running an ASHP, with the incentive deducted, was just as good value as the oil boiler.

An air source heat pump uses electric energy to extract the heat from the air outside the house.

Maria explains: "A refrigerator cools down the inside of the fridge and releases the heat into the kitchen. An air source heat pump does the same – it cools air outside the house, pumping the heat inside."

Tim raises his finger: “But here comes the magic: due to a physical phenomenon called latent heat of evaporation, when you put 1KW of energy into your ASHP, on average over the year, it turns it into 3.2KW worth of heat and hot water in your house."

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What about when it is very cold outside, so it seems there is no heat to extract?

Maria laughs: “Those are working in Scandinavia, in far worse conditions than we can even think of in England. The one we have works as long as the temperature doesn’t fall below -15 degrees Celsius. It needs more energy in the winter to extract the same amount of heat from colder air, that’s all."

Tim adds: "In the summer, it uses barely any electricity to heat our water. And I must say, that it does splendid job there, as even in cold months water was very, very hot."

Asked about disadvantages, Maria and Tim point to requirement of providing a certificate of insulation efficiency – the better the insulation of the house, the greater the subsidy from the government.

"And if you want to claim the Renewable Heat Incentive, the supplier needs to have a certificate for the Microgeneration Certification Scheme," Maria explains.

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“Don’t wait until it’s urgent, because this is going to take longer than you think”, advises Maria. “And talk to suppliers, get references, see local examples of their work to make sure they do domestic refit central heating and know their kit well."

And in the summer it can work as an air conditioning unit.

As the ASHP runs on electricity, it is not carbon-neutral by itself, for which reason Tim and Maria also signed up with a green energy provider Bulb.

They added: “We willingly pay more for electricity to encourage development of renewable energy.

"It is not the cheapest on the market, but that’s not what we were looking for."