Heat pumps

This is our heat pump.  It was cheaper than a gas boiler to install, it's cheaper than a boiler to run, it keeps the house warmer, and it will last longer than a boiler. And with most of the electricity to run it coming either free from solar or cheap from smart tariffs, it's one of the two critical techs to get you to net zero. It feels like a piece of high tech magic, sourcing the renewable heat for your home literally from thin air. It's the kind of thing visiting aliens would introduce us to while cringing at our smoky old fossil burning habits!

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So why haven't we all got one? Well, many of the these advantages only came about recently. In 2017 we first looked at heat pumps and decided against. They were more expensive and noisier than a boiler, and the evidence base for their performance was limited. There were not enough installers -  We could only get one quote. And there were no smart meters or smart tariffs, so you had little choice what you paid for imported electricity.

 

All this has now changed with innovation not just in heat pumps but in electricity tariffs and, importantly, in UK government support for the transition to heat pumps. The Boiler Upgrade Scheme (BUS) offers £7,500 towards a heat pump, which will normally make a heat pump installation cost similar to or less than a new boiler.  This grant is important because, without it, there's no doubt a heat pump looks expensive - maybe £8-12,000 for a typical installation without a grant. Most people would not choose that over £4,000 for a gas boiler, but the BUS grant evens things up. So now is a great time to get a heat pump.

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Can any home have a heat pump?

Yes! You may have seen media coverage saying that heat pumps won't work in British homes. This is not true, it is part of a vigorous, organised campaign by the boiler industry to try and stop heat pumps. But in 2023 a government funded research project examined the performance of over 700 heat pumps in the full range of British housing types and found that all of them - even the old and leaky - could be effectively heated by heat pumps. They also found they were 3x as efficient as gas boilers. This is crucial because, of course, electricity costs more than gas, per kWh. If you want further proof that heat pumps are effective, you can just look at our neighbours, many colder than us, who are enthusiastic users of heat pumps - in fact they are the main heating method in Norway, Sweden and Finland.

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That said, there are some homes which will find it harder to fit a heat pump. The main challenge is in small flats - simply because they may not have the space to fit a heat pump, which is bigger than a boiler. It needs some outside space (wall or roof fitting is possible, but obviously more complex), and it needs a hot water tank or other thermal store for hot water. But if a flat has an airing cupboard type space available, and some outside space, then it can take a heat pump.

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Space will not normally be an issue in a house, even a small house, though be aware that there are UK planning rules which state that a heat pump must be at least 1m from the boundary with neighbours, or otherwise it will need planning permission. This rule seems be based on the old problem of noisier heat pumps, and may change given how quiet many now are. We have to walk right up to ours before we even know if it's running or not.

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What about costs?

You have installation and running costs to consider, and trade off.

Firstly, Running costs are more important! You may spend a few thousands on installation, but in the lifetime of the heat pump (which is longer than a gas boiler, ~20 years), you could spend £20,000 or more on energy, just as you would with oil or gas. Of course, we plan to drastically reduce this, but we need to make good design decisions at the installation stage to do so. If you follow Net Zero Home advice your heat pump should be cheaper to run than mains gas, under current pricing regimes (2023). If combined with the other Net Zero measures on this site, you have the potential to get to net zero cost for your home! Heat pumps are a great net zero solution because they run on electricity, which you can generate yourself using solar PV, which has cheaper smarter tariffs available, and is much easier to decarbonise in the grid too.

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The installation cost is supported by the £7,500 BUS grant, which will make the cost to you comparable to or cheaper than a gas boiler - it is even possible to bring it in for free. Most probably you will pay from a few hundreds to a few thousands. Eg the installer project cost might be in the range £8-12,000, which after the grant is £500-£4,500. This compares with a gas boiler replacement cost of maybe £2-4,000 - and there is VAT on a boiler, but not on a heat pump or its installation.  Whether your installation costs at the upper or lower end of this range will depend on:

• The size of your house: bigger house = bigger heat pump (and maybe inflated quotes)

• The complexity of the installation. Note that it doesn't have to be complex, but some houses and installers make it so. If your existing heating system is complex, or you want extra bells and whistles like zoning, or your installer wants a buffer tank or other non-essentials, then the cost will rise - running costs as well as installation costs, so try to keep it simple.

• Your design flow temperature (ie the intended radiator temperature in cold weather). This may seem like a detail, but with heat pumps it's the most important choice in the design. If you choose a high design flow temperature, eg 50C+, the installation will be simpler and cheaper because you keep the same radiators, but your running costs will be higher, perhaps higher than with gas.

• Your diligence in getting lots of quotes and negotiating - although it is rather a sellers' market right now.

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What differences will I notice in a house heated by a heat pump?

You will have been in many buildings which use a heat pump before, as they are very common in commercial buildings, schools etc, as well as homes abroad, and you will not have noticed anything.

For the homeowner, the only difference may be that the temperature with a heat pump is more even, and the house feel warmer, as the "long and low" recommended way of running a heat pump will deliver more consistent temperatures than the "burn and cool" approach that many homeowners use to save money with gas or oil boilers. And this means that you may change the way you manage your heating. Talking with installers, householders tend to manage their heating in one of two ways: the "set and forget" group and the "tinkerers". The latter are forever intervening and tweaking their heating to fine tune temperatures or save money by turning down/off zones or the whole system. I know because I was one of them! But a heat pump does not work this way - or at least, it will not give the best results from this approach. A heat pump responds well to being left on most of the time, with little temperature variation or zoning, and gives amazing efficiency from this approach, even if it is not perhaps intuitive for many of us who equate economy with turning things down. After getting the hang of it over the first winter, you really can set and forget. We find we are saving money even as the house is more completely and continually heated, having abandoned all the old zoning and tweaking.

Of course, you can set and forget with oil or gas as well, and if this is you then you can keep on just exactly as you are when you get a heat pump. You will probably make even greater savings as you will have had higher oil/gas bills before.

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Other heat pump differences include:

• Space: you will get some space back indoors where the boiler was, and if you have an oil boiler, you can remove the oil tank, use that formerly smelly space for something else,  and you never need to worry about running out of oil again!

• You may be able to disconnect your gas supply altogether if you use electric cooking, thus saving on the standing charge.

• the heating may feel quieter, as the heat pump is outdoors, whereas some boilers make a noise indoors.

• You will cease to have the vapour plume that a boiler produces on a cold day

• One novel effect you may notice is ice forming on the heat pump in colder weather, as the temperature approaches zero. This is a normal effect of the heat pump extracting heat from the air, and it will occasionally automatically run a defrost cycle, just as your fridge does (although you may not be aware of it). This defrost cycle sometimes causes water vapour to rise from the pump - again perfectly normal and harmless.

 

Outside noise can be an issue with a heat pump, depending on your situation and make of heat pump. An air source heat pump has a fan, and it makes a humming or wind noise like a fan, which is louder in colder weather when it works harder.  At its loudest this is similar to a microwave oven, so if you want to simulate the effect, try running a microwave out in the garden in the spot you think you'll use for the heat pump (though you may get some funny looks!). It is unlikely that you will hear it inside the house if windows are closed, which they tend to be when you need heating. Having said that, you may not wish to locate it under a bedroom window, especially if you have single glazing. You will still be using it in the summer too, for hot water.

 

The noise level varies a lot between makes, with older ones tending to be louder, while ours is barely audible at all above about 8C, and even when working harder it's inaudible in the house or outside more than a few metres from the pump . If you think noise may be a concern, check the manufacturers specs for the sound levels, measured in dB (decibels) - there is plenty of variation. While noise is subjective and you may not know what a particular dB level means, it gives a method of ranking heat pumps by noise. Compare the sound power levels and make sure you are comparing the same operational mode. Eg in the example below, the sound power is for A7/W55, which means an outside temp of 7C and flow temp of 55C.

 

 

 

 

 

 

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How low carbon is it?

A heat pump is the only zero carbon heating solution. Forget the distractions of wood burning and hydrogen, these are polluting, impractical, inefficient or all three. A heat pump runs purely on electricity and is therefore zero carbon and zero local air pollution (smoke, carbon monoxide etc)  at the point of use. If you have a zero carbon electricity grid (like Norway or Iceland) then it is zero carbon in operation. If you have a decarbonising but non-zero grid like the UK, then a heat pump is not zero carbon yet, but it is much lower carbon than gas, and its carbon footprint decreases with that of the grid. Current policy is that the UK grid will be zero carbon by 2030-35, so that is when our heat pumps will be zero carbon. Meanwhile a gas boiler put in today will still be puffing out as much pollution then as it does now. 

Because most of the heat energy from a heat pump is renewable, coming from the air around your house, it is cleaner than a gas boiler even if all the electricity came from burning gas! This works as follows: for every unit of gas burnt in the power plant (CCGT) you get 0.6 units of electricity (due to losses at the power plant). The heat pump turns this into at least 1.8 units of heat for your house (assuming a low COP=3). Meanwhile a gas boiler would turn that same unit of gas into just 0.9 units of heat for your house, assuming a 90% efficient boiler. So heat pump  grid emissions would be half that of the boiler.

But we are not using 100% gas fired electricity in the UK; zero carbon power sources (wind, solar, nuclear) exceed fossil sources (gas, coal). And the net zero home generates as much electricity from solar as is used by the heat pump. This means it has net zero electricity consumption, and net zero emissions, whatever the characteristics of the grid around it.

 

Embodied carbon: this is the carbon represented by the heat pump product itself, which includes steel, plastic, electronics etc. The embodied carbon of a heat pump is not zero, it has a carbon footprint if it has been manfactured in any country with a non-zero carbon electricity grid (which is most), and also from the impacts of mining/extraction of metals, petrochemicals etc. While this applies to a gas or oil boiler too, the heat pump is likely to have higher embodied carbon due to being a bigger device than a boiler.  However, the gas use by the boiler is likely to outweigh any embodied carbon advantage many times over - see this analysis  by Mitsubishi.

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To minimise neighbour impacts, planning rules require a heat pump to be at least 1m from your boundary, which may be a constraint in terraced housing. As of early 2024 it is possible government will remove this requirement - check the latest.

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It's also worth noting that there are some very loud oil or gas boilers. Our neighbours have a gas boiler that is audible 30m away, and much louder than our heat pump 3m away.

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How does a heat pump work?

The quick answer is just like a fridge, or air conditioner. Imagine a portable air conditioner cooling your room, the duct through the window dumping hot air outside. Then swap the duct so the cold air goes out of the window and the heat goes into your room and voila, you have a heat pump (technically an air-air heat pump). If you walk in front of a heat pump you will find it blowing out cold - even freezing - air, just like an air conditioner trying to cool the whole atmosphere!

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