Are air source heat pumps any good?

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Are air source heat pumps any good? It’s a question so many people are asking themselves. The problem is that realistic information is pretty thin on the ground, so it’s tough to decide whether to go for it or not.

Some thoughts from one who knows:

My first recommendation is to stay away from the popular press. Comments are often negative with little actual fact or experience behind them. Much better to speak to people who have heat pumps and ask how they are getting on.

As the owner of an air source heat pump (ASHP), I encourage you to think seriously about it. In terms of climate action, they are a definite win. Heat taken directly from the air – what’s not to like?

Gas boilers are much more familiar of course, but they won’t always be an option. Much better to look into the alternatives while you have time, rather than be forced into it before you’re ready.

Common questions:

Let’s address the most common questions and concerns about this new form of energy production:

It runs at a lower temperature, so will the house be cold?

An ASHP does run at a lower temperature – 55°C – but that doesn’t mean your house will be cold. You just need to approach it in a different way. Rather than setting your time clock to turn the heating on and off each time you leave the house, you set the thermostat to the temperature you want, then leave it alone.

With the traditional gas system, heating comes on in the morning so you’re warm to start the day. After that initial blast, the radiators go off while you’re out, then fire up again for your return. Each time the house has to warm up from scratch and because the heat is short lived, all that gets heated is the air.

With an ASHP, the lower constant heat means the fabric of the house has time to warm up with a resulting steady temperature which doesn’t need to be any higher than 55°C.

We still have thermostats in the house with the temperature set to vary according to when we need it most. It never goes off entirely – we just set it lower at night when we’re in bed.

What about energy usage?

I know this sounds expensive, but the reality is that we are saving loads of money on energy. I think of it like personal training:

The gas boiler is a sprinter. It has to work hard for short periods of time, with rest and recovery in between. First thing in the morning, it goes like the clappers to warm the house up so you can get out of bed in comfort. Then it rests while you’re out, before going hell for leather to be ready for your return home. The boiler heats up all it can in the time available – the air – heat that is lost quickly once the boiler turns off.  

In contrast, the ASHP is a marathon runner. It goes at a steady pace over a long time without the need for rest and recovery. Because the heat is consistent, both the air and the fabric of the house warm up. So even when the pump isn’t working the building remains warm. Since the pump doesn’t need to provide sudden heat, it can do its job perfectly well at a lower temperature.

Coefficient of Performance (COP)

But there is another very good reason why the ASHP uses less energy and that is the Co-efficient of Performance. This is the measure of how much energy goes into the system compared to the amount of energy that comes out as heat.

With a gas boiler or standard electric heating the COP is 1:1. This means that for every unit of energy you put in, you get one unit of heat energy back.

However, with an ASHP the COP is 1:3 to 1:4. This means that for every unit of energy you put in, you get between 3 and 4 units of heat energy out. As the machines improve then the COP will also improve and there are already some machines that promise 1:5.

In short – you get at least three times more energy for your money from an air source heat pump than you do from a gas boiler.

Do you have to have a well-insulated home?

If you have a cold draughty house (like ours was originally) then an ASHP will need to work hard to keep up with the cold air coming in. The marathon runner is required to sprint which is just isn’t built to do.  Of course you can have an ASHP but it won’t run as efficiently as it could do. Obviously if the building is well insulated and airtight (like ours is now) the heat from the ASHP can perform well in the marathon of warm home heating. 

So yes, it’s much better to have a well-insulated home. And for more reasons than just the ASHP. Good insulation and airtightness will reduce your carbon emissions, your energy bills and make you significantly more comfortable, so it makes sense to do as much as you can.

Some elements of insulation you can do yourself if you are up for DIY. Others may need a builder. But you are always in charge and can do as much as budget and appetite for disruption allows.

 Is an ASHP noisy?

I was very concerned about the level of noise. I read enough of people’s concerns to know this might be an issue. We asked our supplier to take us to see one he’d fitted already and that soon put my mind at rest. And just to be sure we went for the quietest machine on the market at the time.

There will always be differences between pumps in terms of noise – just as there are with gas boilers and any machines in our homes. Permitted development requirements state that “heat pumps must not generate a noise above 42 decibels within one metre of a neighbour’s door or window.” Heat pump manufacturers say that most pumps produce between 40 to 60 decibels of noise so this is an unrealistic restriction .

This is all very well if you know what a decibel sounds like. According to Audicus 40 decibels is equivalent to a quiet library and 60 is an electric toothbrush.

In fact there have been very few complaints about noise from heat pumps so DEFRA are suggesting that the 42 decibel restruction is dropped from permitted development.

You can read more of the detail about noise here 

We have our ASHP on the flat roof above our living kitchen, so I spend most of my days sitting underneath it. When the weather is really cold, there is a gentle thrum sound, but I only notice this when it’s all quiet around me. But then I used to hear the gas boiler when it came on – it was always very obvious when it broke down because the house was so quiet. In addition, the noisy part of the ASHP is outside the house, whereas a gas boiler was inside.

I have also heard people express concern about noise when you sit in the garden in the summer. In the summer it is unlikely to be running so even if it was noisy, you wouldn’t notice it.

Will we have enough hot water? 

Another concern is that the ASHP won’t produce enough hot water.

If this is a problem, then it reflects the size of the hot water tank, not the ASHP. We have always had as much hot water as needed. My daughter, who also has an ASHP, has two teenagers who are very keen on multiple daily showers and they haven’t run out of hot water yet.

When I asked our provider about water temperature he pointed out that everyone will add cold water in the shower. If you can stand under a constant flow of 55°C water, then you have skin like a crocodile. So water heated to 55°C is hotter than you’ll even need.

Does it take up a lot of space?

The heat pump sits outside the house in the garden on a side wall or flat roof. Ours is a Mitsubishi Ecodan and the dimensions are: width – 1050mm; depth – 480mm’ height – 1020mm. For optimal efficiency, there needs to be a minimum of 300mm around the sides and rear of the pump and 1.5 m of unobstructed space in front. If you need to disguise it, then any fencing must be a lattice to allow for air flow – after all that’s what the machine is working with.

Inside the house there needs to be space for a hot water tank, and a header tank plus the sophisticated electrics and plumbing that make it so efficient. If you presently have a combi boiler that heats water on demand then you will need to find the space to put in all these workings. On the bright side, we now have a really good airing cupboard around the workings.

If you don’t want to place the pump right up against the house, it is possible to put it further down the garden (if that’s an option for you). You just need to factor in the cost of extra pipework and lagging to get the heat into the house.

I have also heard of pumps being installed in flats, so do ask around if you want a non traditional arrangement.

They cost far too much money

The cost will vary, of course, depending on which pump you choose and who installs it. We spent approx. £13,000 three years ago. Looking at various providers on the web, new pumps seem to come in at between £10K and £13K fully fitted. There seem to be some very good deals out there, so it’s worth taking time to search. I’ve also seen some energy providers who provide no interest loans.

Government grants have just increased so you can claim £7,500 towards the cost.

There will be an additional cost for plumbers to link the ASHP system up to your existing heating circuit and if your new ASHP is sited in a different location to our gas boiler then you would need a survey and quote from a plumber.

In terms of money retained, we are now saving 75% of our energy usage after insulating the house and installing a heat pump. So an ASHP is not only good for the climate, it’s good for your bank balance.

Next steps

I hope this helps, but if you’re still unsure reach out to anyone who has a heat pump and ask if you can visit them to learn more about it. If you’re nearby, you can ask me! But whatever you do, avoid the sensational press – they will only wind you up and cause problems where problems don’t exist.

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