My Urban Car

8 things to know about switching from gas or oil to an Air Source Heatpump

Please note, I have had an air source heat pump installed in my Victorian terraced house in Southwest London, but am not an expert in heating or air source heat pumps. This is what I have learnt from being on the homeowner side of the transaction as a result of having purchased a heat pump, having it installed and now having it heating my home and hot water. Nevertheless the pointers below should be useful if you, like me, are interested in switching away from fossil fuels to renewable electricity for heating and hot water. If (also like me!) your gas boiler has just broken down you need this even more! Any of the advice could change as new products come to market but we hope it’s broadly correct currently in UK in May 2021. My Heatpump also a moment of fame on the PM program on Radio 4

My Heatpump’s moment of fame on Radio 4 in Oct 2021

What is an air Source Heat Pump?

Air source heat pumps (ASHPs) extract heat from the outside air to heat your home and hot water. They can still extract heat when air temperatures are very low (even down to -20°C on the Swedish Nibe used here)
Matthew Parris put it rather well in a recent article in The Times
“Imagine plunging a red hot poker into a big bucket of cold water. The temperature of the poker will drop hugely. The temperature of the water will rise slightly. Overall, energy will have been neither lost nor gained but simply transferred from poker to water. Now suppose a machine could achieve the reverse: water cools slightly, poker heats up hugely and, again, only a transfer of energy”
Air source heat pumps need some electricity to run, but because they transfer heat from outside air, the heat output in your home is much greater than the electricity used to run it. While other heating like gas boilers deliver less heat than the energy they use.. (70-98% efficient) an air source heat pump can deliver between 3-4 times as much heat so an efficiency of 300-400%

1. Is your home suitable?

Like me you may be keen to replace fossil fuel gas heating and hot water. With sharp CO2 cuts needed between now and 2030 the prospect is attractive, especially with heat efficiently plucked from the air using renewable electricity. Before you rush off to installers though its best to check if your home suits current air source heat pumps.

  • Is it a new build in planning or construction?
    New build houses or blocks of flats can be designed for heat pumps from the outset, indeed in the UK new builds will soon not be allowed to connect to gas supplies at all. The sooner you involve a heat pump specialist the easier installation will be
  • Don’t let plumbers install microbore heating and water pipes
  • Do install water underfloor heating or check radiators are adequately sized
  • Is it an entire house?
    Sadly if you are one flat in a building currently available heat pumps probably aren’t for you. However if all the flat owners want to share heat and hot water from one installation then continue
  • If replacing a gas boiler in an existing home.. where would place your heat pump?
    Is your existing gas boiler accessible via a wall or roof to a suitable outside space? For example heat pumps are quite big and have to be at least metre from a boundary wall with a neighbour.
  • Do you either have a hot water tank or somewhere to install them. There are currently no equivalents to a combi boiler that provide hot water on demand without a tank
  • The good news is, if needed, heat pumps can use heavily insulated pipes to carry hot water over a good distance from where it enters the house.
  • Detached and semi detached houses should find a space reasonably easily.. while terraced houses like my own require a little more thought and imagination on placement!
  • We have no connection with EverGreen energy but their page here gives an good indication of the planning rules

2. Finding a professional installer

All renewable installations should be be carried out by an MCS accredited installer. Not doing so may void or reduce warranties, remove eligibility for government incentives and grants. Having said this I am informed that MCS is not a professional qualification nor a validation of their ability. There could therefore be both excellent and cowboy installers whether you choose an MCS or non MCS installer.

MCS Installer search page
Quick tip – after completing the boxes including the location of your home and pressing search use the sort by distance box to find installers located closer to you. While some installers from 100 or more miles away do installations I think choosing installers within an hour of your location is useful. Spend a bit of time. Personally I knocked out those:

  • without a working or relevant website or
  • seemed to be a single person operation rather than a team
  • that only worked with one manufacturer or
  • that appeared to be general plumbers trying their hand at installations

Talk to some promising companies. They should be interested in your property, where a heat pump could be located and informative about choosing a pump, your house size, radiators, cost and grants. Some of the best installers will be so much in demand that they might not be able to start a project for months. During my calls even the busy installers found time to give useful advice and were clearly enthused being in this business.

3. Is your home really suitable?

Ok so you think you have a good spot to place your heat pump and you’ve found an installer so just go ahead and order? That’s a start but no!

EPC Certificate
Before you place your order – You need a current EPC certificate to tell you whether your home is sufficiently insulated to be suitable for an air source heat pump and also eligible for the renewable heat incentive scheme (see under cost below). My understanding is you’ll need at least a D but do check. See costs for more info.

Heat Loss Survey

After you confirm you want to go ahead but before the installer orders your heat pump they will conduct a heat loss survey. This is like a more detailed EPC on a room by room basis

  1. For each room the insulation, windows, doors and walls are looked at and a calculation made of how much energy will be required to keep it warm.
  2. The survey then looks at the heat output of radiators based on the lower water temperature that a heat pump produces compared to an old gas boiler. Essentially a room losing a lot of heat may need a bigger radiator!

4. Choosing an air source heat pump

I am not in a position to advise you on this and that is why you need a knowledgeable professional installer who is able to recommend the best option for you from a variety of companies.

What I heard is that the German and Swedish makers have been making heat pumps for homes for years and are a little more expensive. Other brands primarily from Asia have got into heat pumps having been big producers of air conditioning units. They are less expensive but also less efficient and perhaps not as optimised in unusually cold situations. Finally some are just entering the heat pump business having been makers of gas central heating boilers.

I would listen carefully to any advice on these brands and products from your installer. In particular take into account brands that have a poor or unproven reputation for customer service as this is a complex piece of hardware that should last a long time.

5. Cost

The UK Government was just coming to the end of its latest green grant debacle when I was looking to order in Spring 2021. In theory the grant would have provided an up front grant of around £5,000. In reality the Government had randomly stopped paying this to installers who had already installed heat pumps so unsurprisingly installers stopped accepting installations using the grant.

The bad news

Heat pumps themselves are a lot more expensive than just replacing a gas boiler.

  • Gas boiler inc installation – I originally assumed a replacement gas boiler would have cost around £3k but having spoken to neighbours who installed a gas boiler the full installation cost £4k to 5k.
  • Air Source Heat Pump installation – £12k to £14k
  • Until the government provides another up front grant you may have to finance or pay the entire cost yourself. If you are able to do this look at the good news
  • it’s also worth noting that an air source heat pump might be a bit cheaper to run than an old gas or oil boiler but if you are replacing a newer condensing boiler bills are likely to be similar. Although heat pumps are super efficient the fact is energy in the form of gas is cheaper than electricity unless you generate your own power. One option in future may be to use a battery to download cheaper off peak electrify to power your home.
The good news
  • Luckily the Renewable heat Incentive (RHI) remains in place and in my case should repay about £10,000 of the roughly £14,000 installation cost, leaving the heat pump costing about the same as a gas boiler in the end
  • The original £5,000 Government grant would have been deducted from the RHI payments so the total amount you receive has not changed
  • Why is loss of grant an issue then? Well the RHI payments are quarterly over a 7yr period from the commissioning or “switch on date” so, although you get the same amount, the scheme without a grant makes it harder for the many people without £12k to £14k available to cover the initial cost up front
What affects how much renewable heat Incentive you receive?

If you looked at the definition of a Heat Pump above you’ll see they are more than 100% efficient. Essentially the RHI grant pays you based on how much heat energy was delivered over and above that 100%. This means

  • You get higher payments for a heat pump that is 350% efficient than one that is only 300%
  • The amount of energy used and saved is monitored to measure and set your payments. So if your house was so well insulated that it needed no energy to heat (and you had cold showers!) you would use no energy and receive no payments on your heat pump. If you have a band D energy home you will get bigger payments than a home that is band A
  • Although this may seem a little counter intuitive it does succeed in crediting you based on the amount of CO2 saved by your heat pump.

6. Time to Install

I once went to a holiday restaurant with a prominent sign that said “If you’re in a hurry you’re in the wrong restaurant”. Likewise a retrofit of an existing gas heating system in winter is not quick so I would urge you to carry out the changeover when your existing boiler is still running or ensure your old boiler breaks down in summer not winter! That way the changeover period without heat will be a matter of a day or two, not weeks.

DateTask Schedule
8th Feb 2021received quote
11th Feb 2021Deposit paid
16th Feb 2021received EPC certificate
19th Feb 2021Switch from Vaillant aroTherm 10kW model to a smaller Swedish Nibe F2040 12kW pump
23rd Feb 2021Heat loss Survey
5th Mar 2021After a delay Nibe delivery est week of 15th March
22nd Mar 2021Nibe heat pump actually delivered/ installation begins
11 days installation time
7th Apr 2021Heat pump commissioned and providing hot water and heating

From around the middle of January 2021 when our gas boiler had to be shut off because of dangerous levels of carbon monoxide we relied on an immersion heater for hot water and for heating
1 DYSON Pure Hot+Cool Advanced Air Purifier and 1 Dyson Hot + Cool AM09 Fan Heater
While I’m sure the electricity bill took a hit, it was quite remarkable how these 2 Dyson fans and some light jumpers managed to make outside temperatures down to -9C manageable in a Victorian house.

As you can see from the schedule, a winter installation after your boiler has been taken offline is one for the brave, determined or foolish! The biggest time losses were finding a good installer, getting on the schedule for the installation team and the time for the heat pump to be delivered. Do bear in mind most really good installers will have weeks or even months worth of installations already scheduled. Some we spoke to were perfectly open in February that the soonest they would be able to install was june or july!

The 11 day installation time involved a couple of days of less activity, most days with 2 members of the installation team and a couple where 3 to 4 were needed for specific tasks. If all parts had been available when needed it might have been cut to a 7 working day job.

For this installation I used Elite Renewables. Although there were delays they were exactly the kind of installer I would recommend. Everyone from Martyn Fowler, the director I first dealt with and everyone on the various steps to James my lead installer was friendly, knowledgeable, professional and happy to answer my endless questions in a way I could usually understand!

7. Size and space

You might think that with a large heat pump outside your home that would free up space on the inside. Think again! Every manufacturer has slightly different kit requirements but a Heat Pump is an almost magical but also quite technical piece of kit to install compared to a gas boiler. There are lots of parts needed to perform this magic.

  • We picked a Swedish Nibe F2040 12kW pump
    Its 89.5cm tall, 1035cm wide and 42.2cm deep. It weighs 90kg
  • The originally planned Vaillant aroTherm would have been slightly more efficient but 97.5cm tall, 110.3cm wide and 46.3cm deep and weigh in at 126kg
  • Essentially the air source heat pump has a fan and condenser. Some also contain the water pump but on ours this is in the house
  • In the house there is a buffer tank. Essentially the hot water for heating and water comes from this buffer tank. The air source heat pump then tops this up as needed. There are also expansion tanks which were also new.
  • In the house there is a control system box, a lot of pipework, 2 water water pumps (there are 2 separate circuits for the water from the pump to a buffer tank and then from there to the heating and hot water
  • We had a megaflow hot water tank at mains pressure in the basement. Unfortunately this also needed replacing (all included in the quote) because heat pumps need a bigger heating coil to get your hot water heated enough.
  • My understanding is all heat pumps come with an immersion heater as back up in your hot water cylinder. Not because they are unreliable but because every few weeks the immersion is briefly used to increase the hot water temperature to protect against legionella.
  • Do check the sound rating of your heat pump. Ours has a quiet rating but I really wouldn’t want it to make more noise. Noise is most not surprisingly in cold weather when it is working hardest. It is very quiet when windows are open in summer. Do ensure yours sits in the foam tracks that are made for them – a harder surface like concrete tiles will increase noise and vibration.
  • one plus point of a heat pump is no more lethal carbon monoxide coming out of a flu pipe. Which means it’s no longer illegal to open the window next to where the flue used to be.

8. You don’t have to be hot to be warm

You have probably heard that the hot water from air source heat pumps isn’t as hot as from a gas boiler. That is correct – usually it’s around 50C.. mine is just below that. So without replacing any radiators and without any underfloor heating what has it been like to live with?

  • Luckily despite missing most of the winter, April 2021 was one of the colder April’s with a record number of overnight frosts so a reasonable test of the heat pump even if next winter will tell me more
  • If you arrived back to a cold home and in English style wanted the house to be warm in half an hour you would be disappointed. Getting up to temperature might take a day or 2 in cold weather. So that is not how you use a heat pump
  • Instead you tell the heat pump how warm you want the house to be and your heat pump simply keeps it at that comfortable temperature all the time. The heat pump runs most efficiently that way and keeps your house warm effectively that way too.
  • Leaving it running works. Even though, to the touch, your radiators rarely seem more than lukewarm. It doesn’t feel like it should work but it does. It probably leaves the air in your home with more humidity too.
  • We have some rooms with oversized radiators and others that are undersized which always left these rooms a bit cold when our gas boiler switched back on after cooling between timer cycles. While it is hard to be sure till we get into another winter, the permanently lukewarm heating seems to keep even the rooms with undersized radiators much better heated than the gas “hot heat” to “no heat” cycles.
  • The only room that is a little cold is the downstairs toilet that used to be home to our boiler. Although it still contains our heating equipment and controls it is all so well insulated that the room is definitely cooler having lost the waste heat from the gas boiler.
  • Provided your radiators are close enough to the output they need and you use the always warm approach your heat pump should be able to keep you nice and warm. Do remember that insulating a room better including with double glazing could be a better alternative to bigger radiators

Would you/ should you still switch from gas to an air source heat pump?

Yes yes yes! The fact is we need to roughly halve our carbon emissions between now and 2030. In essence though when you ask the question “how can I heat my home efficiently using renewable power instead of burning fossil fuels” air and ground source heat pumps are currently the only convincing option. While some want to push hydrogen it simply doesn’t achieve the goal. Currently 90% of hydrogen is produced from methane (worse for heating the planet than CO2!) or produced from electricity so inefficiently you would need many times the electricity production to heat the same number of homes.

Gas central heating has had a good run but is close to being phased out.

The UK government is likely to announce new rules and incentive arrangements in order to help decarbonize domestic heating in line with climate change science based targets. Bloomberg reports that in 2020, 20.8% of UK CO2 was produced by domestic heating.
There are issues with heat pumps including cost but this is largely compensated for by the renewable heating incentive.

It does take a little more time, complexity and cost to install but my experience to date is it heats the house better all day long than our gas boiler on off cycles. It may be best if you think about it not as a direct swap for a gas boiler, but a step into a whole new low carbon heating upgrade for the future.

What do we need for this market grow and thrive?

  • What we do need to see is heat pumps come down in cost as installations grow from around 35,000 a year today to millions a year by 2030
  • Even though heat pumps do vary in design I do think the extra kit that comes with them should become more standard between different brands. This will lower cost and reduce the amount of equipment that needs to be renewed when you eventually need to replace your heat pump.
  • Work also need to be done to make heat pumps easier to install. Currently the training and knowledge is something that would be challenging for an existing heating engineer to transition to quickly and we need them to convert to installing heat pumps in their tens of thousands.
  • We also need new products that can be fitted to a wider variety of homes including more retrofitted houses and flats.

This will all happen as the heat pump business grows and matures.

The video below is an interview of the client and installers of a domestic air source heat pump in Scotland.

David Nicholson

David Nicholson Is the founder of Rivergecko Ltd & MyUrbanCar which provide consultancy and advice for drivers and fleets to speed the transition from dirty fossil fuel transport to clean vehicles powered by renewable energy on land water and air.

The @MyUrbanCar twitter feed is a source of news & reviews of electric & plugin cars and vans in the UK.
The @rivergecko twitter feed & websites bring news and opinion on cleantech transport including cars, vans, buses, trucks, shipping, rail & aviation as well as autonomous vehicles & renewable energy, air pollution & motor industry news.

David Nicholson has worked as an underwriter at Lloyd's of London since the 1980's. His interest in technology goes back many years including interactive mapping, apps, green tech, boats, solar and cars.