We used easy bolt-on measures to achieve Net Zero Carbon and Net Zero energy bills, with a good payback. Here's how we did it.
A few years ago we made the typical switch that many new parents make if they can: out of a city flat, and into a house in the countryside. Just as typically, the house was in a bit of a state, structurally sound but with cracked render and blown double glazing. Couldn't see all that on a sunny day though...
It also came with a thirsty 30 year old oil-fired boiler, and in the garden was big oil tank, and in just 6 months we paid £1200 to have more of the smelly stuff poured into it.
I work in sustainability, and it had always been my ambition to have some kind of eco-house. But we never had either the site or the money to construct one of those white glistening edifices, filled with the latest gadgetry, that you see Kevin McCloud enthusing over.
The alternative was to retrofit. And to be honest, I preferred this option - and not just because it was the only one we had (apart from continuing to shell out £2,000+ per year). But more importantly, most of the housing stock we will live in in 2050 is already built. To get to net zero, we have to retrofit what we have. I wanted to achieve this in a way which could be replicated by most house owners, and crucially, was affordable - even profitable. The transition to a clean future will never work if we all have to pauper ourselves to do it, and many sceptics, especially in the media, are always claiming it's unaffordable.
So - spoiler alert - we did it, probably sooner and more easily than I would ever have dreamed! We're saving thousands too. Here is how it worked, and you can use the how-to guide that we developed to help you do the same on netzerohome.uk.
Planning the net zero home retrofit
So you're faced with a new (to you) house. It's a big mass of masonry after your old flat. It has holes, cracks, gaps, cold bits, warm bits. You have general headings in your mind: solar, heating, insulation. Fix the holes. Make the cold bits warm! Make the place look nicer. And how much money have we got to do this? We made some savings on the purchase price because of all those holes and cracks, but what to spend where? I knew a bit about sustainable energy, but not so much about bricks and builders.
So we didn't know everything, but we could set out some priorities. The first bit was nothing to do with net zero; we fixed a big hole in the roof! Easy choice. But then we faced choice paralysis. On the Energy Menu were solar panels; gas boiler (or heat pump?); new double glazing (or triple?); external wall insulation? But there was the Nice Home menu too: redecoration; carpets; sort out knackered kitchen, bathrooms, windows and render. And strangely enough, a limited budget. A microcosm maybe of the world (or at least the developed world) going into the energy transition.
And this is where, luckily, we managed to figure out the big picture: this was not a house in need of an energy refurb. It was a house in need of a refurb. Yes, we could make some improvements to the fabric along the way, which would insulate and save energy. But these would never have made any financial sense for energy reasons alone. So this is the first big lesson: Do energy work in line with your wider maintenance and refurb plans. That way you do the work you were going to do anyway, but the net zero way. It will often cost very litttle extra. This approach can of course delay your progress, but that's better than unsupportable costs (this of course applies to the whole economy too).
With this in mind, our array of options fell into two main groups: the straightforward, cheapish, standalone bolt-ons, versus the scary expensive, dusty refurb. We decided to progress the former while planning the latter.
Moving on from oil-fired heating
The big oil bills made it obvious to focus on heating first. A surprising apparent bonus with the house was a gas connection. Yes, gas connection, oil heating. Go figure. The connection was only used for the hob. So a dash for gas was one option, and we got quotes for a shift to gas central heating. But what I really wanted was a heat pump, I knew this was the low carbon option, so we got quotes for that too. Correction, one quote. In 2017 a heat pump was a rarer beast than now, and we could only find one local installer, who wanted £11,500 to install a 11.5 kW heat pump. The cost would be defrayed by the renewable heat incentive (RHI) which was then the relevant support mechanism.
Long story short, we didn't go for it. The financials were ok, just, but there was a real lack of evidence about how well it would perform, and what there was suggested the supplier's performance claims were fanciful. The carbon numbers for gas still offered a big saving, and I was just slightly uncertain over whether we'd be warm enough. Climate change may be very scary, but a cold family is too. And finally, at the reference site we went to visit (always insist on a cold day), the pump was quite noisy.
So we went for gas. Still quite expensive by the way - you keep hearing about £3k installs but that is only the simplest. Our old oil boiler exhausted up the chimney, we weren't allowed to keep that internal location due to new flue rules, so we had to shift it across the house. £7,000 in the end. So remember gas is not always a cheap option! But we still cut our emissions in half, and fuel costs by about a quarter.
Solar PV or not?
Surprising as it seems now, I was not initially wedded to the idea of getting solar panels. We have an attractive pantiled roof, and I was worried about the change in appearance. We all want our house to look nice. So I took to Photoshop and mocked up pictures of how the house would look with PV panels. This worked very well and reassured us, so we got planning.
Solar PV panels are literally a bolt on technology. For most people you choose your supplier, and they will recommend their preferred panels, and the internal electrical unit known as an inverter. But I wanted to get the max power out of the minimum size array, so I wanted the highest efficiency panels available. There was only one clear leader in 2017, which was US company Sunpower. This at least made choosing a contractor easier. There were plenty of options then as now, and they are all required to be certified by UK body MCS (as for heat pumps). They are required to provide you with an estimate of annual electricity production, and financials which help you decide whether this makes sense. Quotes were quite similar, all in the £6-7,000 range, and as with any building project, we picked the local firm which we thought had the best balance of professionalism and price. They arranged scaffolding, and put the 4kW array on in one day.
It was a great moment to see energy flowing out rather than in. Once you have solar, you can't believe others just sit there under barren, baking roofs paying for power when they could have it for free! In the first year we generated 4500 kWh in the East of England, cutting our electricity use by 40%. I have to admit that, even six years later, I still get a kick out of it. As power prices (including what we earn for export) have risen, our savings and earnings from solar have too, so that we expanded it this year by putting 6 extra panels on the garage. With cheaper panel prices that was only £2500 for 2.4kW, and it looks like giving us a 20% return on our investment!
So how scary was the refurb?
First, it was scary because the money was bigger. But how big? What was worth spending? What would the savings be? What would the house end up looking like? It wasn't exactly beautiful to start with (see above), but a quick way to lose money is to ruin the appearance of your house.
As a sustainability consultant I'm used to giving advice, but here was the time we decided to get some instead. We had an architect put the house through some energy modelling software, to answer some of our questions and help us work out how much to spend and on what. This told us our windows were the leakiest part of the house with one third of all heat loss, which was handy because we found them ugly and they had deteriorated badly. But it also told us the walls were thermally good. And it costed various other measures, revealing the most cost-effective measure of all - trebling the loft insulation. This was just £500 (and a dusty day's work), and saved about 12% of our energy bill.
But best of all was that the architect process, and the quotation process that followed, also told us what we didn't have to spend. Or, put another way, what we would have to spend regardless of our energy saving aspirations. Because it turns out it is not that new energy-saving windows are expensive... it is all new windows that are expensive! According to checkatrade a new set of windows will set you back around £20k, and that's just for standard double glazed uPVC that meets building regultions. But get this: it only cost us about £3k to upgrade from double to triple glazing. That was the cost for the high performance, getting our U-value (the critical heat loss parameter for building materials) down to about 1, vs 1.6 for building regs and maybe 2.5 for our old windows. This is why you do your energy work when you're doing your wider refurb work. Such a cost would never have made sense or paid back through energy savings alone.
It turned out the same applied when we re-rendered the house. In this case the difference was a whole £0! This is because insulated render attracts VAT at only 5%, which cancelled out the extra cost of the insulated layer. So even though our walls were already thermally ok and the insulation would only take a little off the heat loss, it was free so we did it.
After that we took time off from refurb. Time when other developments begain to pile up, both good and bad. Global temperature records kept getting broken. The UK government (and many others) declared a climate emergency, setting a Net Zero target, rather than the 80% cut by 2050 that had been in place when we started our planning. UK electricity generation cut its carbon by far more than I had expected when I did our original gas vs heat pump calculations in 2017. Gas and electricity prices soared after the Ukraine invasion. Solar panel prices tumbled. And new innovation in the energy sector saw new smart tariffs available, for both the imported electricity you buy, and the PV power you can sell.
All this meant that by 2023 there was a case for some further changes, and all with a positive bottom line! The easy one was to add some extra solar panels on the garage, as mentioned above. While the main point of this was to earn money through export using the Octopus Outgoing fixed tariff, it also had the benefit of raising our cloudy day production from around 3-400W to 4-600W. This would cover most of the power required, on an average winter day by a ... heat pump.
Heat pump redux
Yes, it was time to revisit this decision. New heat pumps, new evidence and new government support meant that the argument had changed. I was initially doubtful about the timing - after all our gas boiler was only 6 years old. But lots of spreadsheet modelling convinced me that it would pay off. (In fact, the heat pump cost may be paid off before we would even have needed a new boiler). I felt more confident in heat pump performance, partly because of new evidence like that from the Electrification of Heat programme, partly because our house was now less leaky, but also because I had become much more familiar with all of this. Finally, I calculated that this would enable us to get to Net Zero carbon, and even (yes, it was a surprise) Net Zero cost.
So, how to close this particular deal? Well, I could have just asked a bunch of installers round for quotes (there are more installers now). But our first go at this had not been positive. I hadn't been able to make an informed judgement on the quote: the size of heat pump; design features; likely performance. So I wanted to do some homework to get an idea of what we should be looking for in these areas.
For this I needed two things: 1. Data, of course. 2, Social Media. Social media? It turns out that there is a lively heat pump social media scene (!), and I had absorbed quite a lot from the esoteric debates, (not to mention rants) between installers and other experts. That the flow temperature of a heat pump is critical to its performance, and therefore costs. That careful design is more important than which heat pump brand you choose. And that hydrogen is absolutely rubbish as an alternative form of home heating (it needs 6x as much electricity. 6x!).
So back to data. I know not everybody loves data, or even numbers, but they are the way to know things and prove things for certain and luckily I get on well with them. I used my smart meter data to see how much gas we used on the coldest day. That told me how big the heat pump has to be, as it has to be able to deliver this much power. I experimented with heat pump style lower flow temperatures on our gas boiler, to see if our radiators could still deliver enough heat (answer: fine in all but 2 rooms). Then I crunched numbers to see how much electricity a heat pump might use, taking into account our solar PV production and the new smart tariffs, and compared these to our gas use. I couldn't be sure about our hypothetical heat pump performance, so I tried it with several scenarios, to get the best and worst case. This told me that, if I was unlucky or someone, most likely me, screwed up, we might save no money vs a boiler, but we probably wouldn't be worse off.
Now this may all sound like a lot of bother, you can't expect everybody to do this. I quite agree, and this was a major reason I set up netzerohome.uk. There you can read our distilled learning on Getting a Heat Pump, but here are our top tips for a cheaper installation and bills that are less than fossil:
Heat pump top tips
Don't assume you need extensive extra insulation. Most houses don't.
Keep the installation simple. Avoid zoning, low loss headers or buffers. Try to keep your existing hot water cylinder. Take chances with radiator sizes, if you're wrong about a couple it's cheap to upgrade.
Avoid oversizing: the coldest day trick above will tell you how big your heat pump really needs to be.
Use smart electricity tariffs, they can drastically cut your bills.
Exploit the synergies: solar PV is a great investment anyway, but even better with a heat pump. Surprising how many cold but sunny days there are in winter.
Make sure you run your heat pump "long & low". Don't try to burn & cool the way many people do with a gas boiler, it will cost more.
So how did this all work out in the end? Heat pump performance headlines:
Installation for just £800, on top of the £7.5k grant. ie £8,300 project cost.
This simple installation is delivering an efficiency (SCOP) of 4.5. You need 3.2 to beat gas.
At the time of writing (midwinter), our real heating costs are roughly halved compared to gas, helped by smart tariffs and solar input.
The house is warmer than with gas, due to long and low running.
The Net Zero Home is reality
So now we've done the sums and we're there. Zero net energy cost. Zero net carbon emissions. We encounter some disbelief, but you can see the process in the graphs below. Note where the zeros are! We spent about £14,000 on energy related stuff to get here, demolishing the roughly £1,500 we used to spend on energy bills - 11% return. The fabric energy efficiency work knocked around 35% off our energy bills, and for the house size delivered an energy demand (including electricity for appliances) of around 50kWh/m2/year, which is better than a UK new build home, although not quite PassiveHaus standard!
So why do I say it was surprisingly easy? All the important bits were not expensive or disruptive - just a case of bolting on solar panels, heat pump, loft insulation. In the case of the smart tariff, you can switch in less than a minute. The big house refurb items - render, even the kitchen etc - were much more time consuming, disruptive and expensive, and marginal to the net zero accomplishment. This is also apparent from the graphs below, which show that the smallest improvement came from the biggest work, steps 2 to 3. That's why we suggest only doing this if the house needs it anyway. Send it to the bottom of the list.
It does of course help that we didn't screw up or have bad luck - mistakes can be costly and stressful. And it did take some serious work to analyse our actions and minimise the risk of errors. And there was some good luck - the emergence of smart tariffs with major savings, for example, was not inevitable.
Wouldn't you have expected it to be harder? Perhaps not even possible? It is this belief that is perhaps the biggest net zero obstacle. Not just for individual houses, but for other sectors and the whole global economy. Everywhere there are naysayers complaining that Net Zero is impossible, or unaffordable, or will make us cold and miserable. Some of them are the predictable vested interests - such as housebuilders and fossil energy and car companies, speaking openly or through hidden PR channels, bots and clickbait media. Others are more innocent, perhaps lack much science background, and take on these messages, mix them with the natural human wariness of change, and proliferate them. But who should you believe? The reactionary alliance of the biased and the uninformed, or the real experience of those who've done it?
And if sorting one average type house turned out to be surprisingly easy, what might this mean for the rest of Net Zero?
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