As part of the green transition a lot is said about heat pumps. Some of it is nonsense. They will never be the answer to everyone’s heating needs, but neither are they irrelevant to reducing our carbon footprint. They will suit some people and some buildings, but not others. So, what are the issues?
What is a heat pump?
Heat pumps have been in successful use in Scandinavia for decades, but are relatively new in the UK. Essentially a heat pump is like a refrigerator running backwards. Whereas a refrigerator cools the inside and disseminates heat through the coils on the back, a heat pump reverses the process, warming the inside (via water for radiators, or air) while cooling the outside (air or ground).
Pros
Heat pumps are good for the environment. Where oil and gas boilers burn fossil fuels and put carbon into the atmosphere, heat pumps use electricity. Provided the electricity is generated from renewables they produce no carbon. And they get 2–3 times more heat out of every unit of electricity than electric fires or radiators. And, as the Scandinavians can testify, they can still extract heat from the outside air, even when that air is well below freezing.
Cons
However, they are not simple substitutes for traditional central heating. Because they work at lower temperatures than a gas boiler, they take longer to warm a room from cold. So they need to run continuously, which makes them especially suitable for underfloor heating systems, where steady low-level warmth works well. They still can work with radiators, but because of the lower temperature, some houses will find that those need upgrading. They heat domestic water, and once a week they run a sterilisation cycle for an hour or so to protect against legionella.
They also need space outside and inside the house. An air source pump needs good air circulation, so it can’t be tucked into a corner out of sight, and the fan makes some noise – though they are getting quieter – but it could annoy neighbours. Inside the house, a water-based system needs a storage tank, like a traditional immersion heater tank, plus some extra equipment.
Heat pumps are more complex than traditional boilers, so you will need an expert assessment of the house’s heating needs before going ahead, and there is a shortage of skilled technicians to do this, and to install and maintain pumps. Because the government is keen to encourage the switch from oil and gas to electricity, grants are available to help with these costs, but even with those, a new heat pump is likely to cost more than the grant to install. In the right circumstances the extra cost will be recovered over time, but you do need the capital up front.
But critically, they will only work if the building is sufficiently insulated. Otherwise, you are wasting energy heating the outside, through windows, walls, roof and draughts. For that reason, government grants used to be only available for houses with Energy Performance Certificates rated at A-C. That requirement has been removed, but if your house does not meet that standard, you should think carefully about whether to go ahead.
Three case studies
Three of us have experience of heat pumps. Each is different, but together they can shed some light on how to think about switching.
A – Stephen – ASHP with radiators in a very old house
We live in a very old, four-bedroom thatched house with solid walls and floors, double glazing throughout and substantial loft insulation. There is no mains gas. The very old oil boiler was running 23 radiators, including a large conservatory (only heated for frost protection).
The house narrowly scraped an EPC rating of C, so there was a grant. Since we had sufficient savings, we bought a large, Daikin high temperature ASHP five years ago, expecting that it would turn out cheaper as oil prices rise over time. We only had to replace three radiators.
For a couple of fairly sedentary pensioners at home all day, it works well. It keeps the whole house at a steady 21°C throughout the winter. We have a woodburner in the living room, but mainly because we like the look of a visible fire, not because it is necessary. One trivial mistake, our outside unit faces the back door, blowing out cold air. We never leave the door open when it is running!
On balance, this works about as well as the old boiler, and the running costs are about the same. So, in these circumstances, don’t expect to save money. For us, the heat pump made sense because we had savings to pay the initial costs. It was always an investment in the future of the planet.
B – Kathryn – ASHP with underfloor heating in a modern bungalow
I bought a well insulated bungalow, built in 2013 with an EPC rating of C. It came with underfloor heating throughout and an outside Vokera air source heat pump. Each room has separate thermostat controls.
The village has no gas, and I was used to a gas boiler. So I had to adjust my thinking on how to heat the bungalow. Since it takes a good 18–24 hours for the room temperatures to rise from cold to a comfortable temperature, I learned to run the heat pump 24×7. Room thermostats adjust living room and bedroom temperatures. Only our dog found the living room floor too warm.
Like a gas boiler, there is an annual service of both heat pump and the underfloor heating valves which sometimes stick leaving cold patches in the floor. The main challenge has been servicing. The company which previously serviced Vokera heat pumps now say they are happy to service them, but they cannot repair them!
There have been no major issues, the heat pump is a bit noisy but not unduly. Thankfully, we have a wood burning stove as power cuts do occur in rural areas, so we always have a means of warmth and basic cooking.
C – Elana – GSHP with underfloor heating in a new build
Our old house collapsed during renovation. So we had to rebuild, to high insulation standards which met the EPC test for a heat pump grant.
Where an air source pump takes its heat from the air, our ground source system takes it from the earth. Fortunately, there was enough land around our house to enable a couple of miles of trenches 1.5m deep to loop the pipes carrying natural warm water from the ground (8-12°C in the UK), around and into the house. Here, the heat pump raises the temperature for use in the underfloor heating system for both up and downstairs. Since 2000 the system has been completely trouble free. The house stays permanently at a comfortable 21°C all the year round. We also have a woodburner to top up occasionally.
Although the initial costs were relatively high at about £12,000, the government grant covered half those costs and the quarterly payments for the following 7 years more than covered the rest as well as the running costs. What we have is an environmentally friendly, low-carbon and sustainable system that is also extremely efficient, reliable and cost effective.
So, ask yourself
- How well insulated is your house? Does it have an EPC of C or better? If not, consider improving insulation first.
- Do you have sufficient space for the inside and outside units?
- If you want a ground source pump, do you have enough land?
- Do you have, or can you raise, the capital required to top up the grant for installation?
- Do you want to lower your carbon footprint?
If so, a heat pump may be right for you. But make sure you get more than one quote and assessment of your needs.
In Norwich, ‘Our Power’ is a Community Interest Company which introduces people considering heat pumps to people who already have one, so you get a chance to see it and talk about the pros and cons. They are organising an event ‘Future-Proof Your Home: green home upgrades explained’ at 7.30–9.30pm on 24 March at the Norwich Quaker Meeting House.
You can book your place at https://future-proof-home.eventbrite.co.uk
Or if you are interested the Heat Pump Buddy scheme you can email heatpumps@ourpower.org.uk
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