There’s an unlikely sentence, what is he on about?

Blog post from Stephen Cockett – General Manager WCE.

Even as a bit of a green-tech-energy-geek there are always new things to learn, and just a few months ago I learnt a whole lot more about air-conditioning. And the headline there – if you can’t get the bottom of this post – is that air-conditioning works very well in reverse. Just as it cools air, air-conditioning will heat it.

Now why is that a thing that I am excited about when we all associate air-conditioning with being an energy guzzling extravagance? Well, it’s all about the efficient heat pump inside.

Heat pumps are a long-established piece of simple technology, and 98% of homes have got one already in the form of our fridges and freezers. Air-conditioning uses that exact technology to either heat or cool the air, that’s wonderful you might say but still why is that a good thing? Well, you’ll no doubt have heard a great deal of noise from the government and others about heat pumps and the reason for that is efficiency. A heat pump will take one Watt of electricity and turn it into approximately four Watts of heat.

On that basis it is immediately clear that if you have all electric heating in your house – like 10% (7,200) homes on the Isle of Wight – then your like-for-like running costs for heating can be reduced by 75% by changing to air conditioning, or as it might be better referred to, by changing to an air-to-air heat pump (A2AHP).

Outdoor unit, with a potenial heat output of 8 kw

So, how does it work? From what I can tell it’s a mysterious mix of chemistry and physics, and the easiest way I have found to explain it to myself is – when you squeeze and release gas under a certain condition it soaks up lots of energy from the air around it – and that energy from the air is where the 1 to 4 energy efficiency comes in. You get that heat push it down pipes and then a through a heat exchanger (a sort of radiator) and the heat pours off into the room.

And what kind of job is it doing? Keeping in mind that I am only one month into A2AHP ownership, but so far, fantastic. Until now our house has only had expensive to run electric heaters, which we have supplemented with a log burner. We have replaced the electric heaters in the living room, the office (where myself and the wife spend much of our days) and in the kids room (where the nipper spends ever longer on the Xbox..).
The heat produced by the wall units is blown out by an internal fan, which at first might seem unsettling and draughty, but we’ve not noticed that at all. When it comes to first switching them on, they do make a fair bit of noise as they blow strongly to heat the room, the upside of that is going from cold to warm in a matter of minutes. No hanging around, and there is no need to set timers to have the heat on before you get up when the room warms in the time it takes to make the coffee.
Once the initial heating is done the units settle down and produce a consistent warm airflow that can barely be noticed, not unlike the heat that comes from any regular heater you might be familiar with.

Wet dog tucked in next to the heater after a chilly walk.

And what does it look like? It looks like a box outside that hums quietly and heaters on the walls inside that sit either on the floor or up on the wall where you normally expect to see air-conditioning units.

4.5 kw floor mounted unit – ample heat for half the house!
2.5 kw wall unit – more than enough for a bedroom.

And what does it cost to run? Watt for Watt they are a quarter of the price to run of a conventional electric heater, but what does that mean in day-to-day use? For that we need to look back at our previous consumption and gaze into the future a little. I have been tracking our consumption for the last 6 years and tells me that we use around £1,000 in extra electricity over the six winter months compared to the six summer months, nearly all of that can be put down to heating. So, we could theoretically reduce that to £250 for six months heating. Alternatively, we could spend the same amount (£1,000 over winter) and have four times the heating! Realistically we will probably settle in the middle, that is double the heat for half the cost as we were never really warm enough in the house before and relied a bit too much on the log burner – which we are inclined to use less and less.
So I am guessing that we will spend – on heating – around £3 per day for twice the warmth we had before – the first meter reading suggests that might be £3.50 a day for a good sized 1960’s house. A considerable saving, for a large increase in comfort.

What energy geeks do for fun, six years of tracked household electricity use, clearly showing the winter peaks.
For info, this data also includes an electric car which was added between winter two and three. And solar PV added in the last year.

And what does it cost to install? First a bit of context. A quick search around the net suggests that a traditional gas fired heating system would set you back in the region of £6,000 to £8,000 for a house such as ours, and then cost around £900 a year to run. An air-to-water heat pump to replace the boiler and use the radiators seem to cost in the region of £12,000 to £14,000 for a typical instal, minus the government grant of £7,500 leaving a cost hovering around £4,500 to £6,500 for the homeowner to pay. And what did ours cost? £5,700 all in.

Trucking outside the house that connect the units

What did we get for the £5,700? In terms of material, we have one outdoor compressor unit and then connected by pipework we have two floor standing heating units and one further heating unit that pops up on the wall.
So only three units for a whole house? Yes, for now at least. The outdoor unit does have the capacity to run an extra heater and we may choose to install one more in the future, we didn’t install now for three reasons, firstly the costs were already significant for us, secondly the fourth unit would be in the main upstairs bedroom which is a bit hard to route the pipework to and that room does get the warmth from downstairs funnel up to it, and we are quite happy under our big quilt so no need to spend an extra £1,000 or so.
We have AMPLE heating from the unit’s downstairs which quickly heats the spaces and provides enough heat to warm the upstairs by convection.
We have lower energy costs thanks to the 1-to-4 heat pump efficiency.
And we have added value to our home.

What is the payback? We can assume around ten years for the upfront costs to be returned thanks to the day-to-day savings.
Other than that, not having rows with my dear wife about the temperature of the house? Priceless.


  • Instantly controllable room by room.
  • Puts out buckets of heat rapidly.
  • Cheaper to run than gas  and much cheaper than conventional electric.
  • Lower energy use from a grid which (slowly but surely) is using less and less fossil fuel.
  • Air-conditioning thrown in too! (when we get the odd hot day we might use it in the office and then it’ll run for free from our solar)
  • Availability of installers, our wait for quotes and our install was measured in weeks not months.


  • You still need to heat your water elsewhere, unlike an air-to-water system, – currently we have a typical immersion tank.
  • A touch of noise and a tiny bit of air movement, more than a ‘touch’ when first warming the spaces.
  • No grant funding – though it was VAT exempt.

Local Installers.
Wight Community Energy will not endorse any individual firm, but there a several well regarded air-conditioning contractors available on the Island who can supply and fit a variety of systems from different manufacturers.