Viessmann Heat Pump - Heat pumps vs solar panels

Air Source Heat Pump Regulations

Air Source Heat Pumps are fantastic for certain
homes. But there are a lot of rules around the £7,500 grant.
Find out more below.

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Air Source Heat Pump Regulations

alpha magis m air source heat pump

Introduction to Air Source Heat Pumps

So, you’ve decided an air source heat pump is a good fit for your home. It’s a great idea, we love them. They don’t burn fossil fuels, creating carbon-based emissions during use and could be used alongside photovoltaic (PV) panels to provide you with completely free (after installation) heating and hot water.

Plus, great news, there’s a government grant available of £7,500 to help you pay for it. If you would like to get a quote for an air source heat pump, please contact us on 029 2009 9898 and we’ll be happy to have a chat.

We are a Viessmann premium supplier. We work with Viessmann because of their quality manufacturing processes and industry-topping long warranties on products.

Let’s begin…beware, there is a lot of misinformation out in the world.

Air source heat pumps work best, and very well, in specific conditions at well insulated homes. They need to be set up correctly to ensure their high efficiency. If they’re not set up right they can cost you a lot of money by working harder than they should and this could also shorten lifespan.

We’ve tried to create a detailed and honest guide to answer all your questions surrounding what is and isn’t possible with air source heat pump installations. We’ll need to go through the heat pump units, the pipework, the radiators, insulation and more.

Please bear in mind that all homes are different and will have slightly different set ups and requirements.

Each of the below steps is something you will need to consider when thinking about highly energy efficient air source heat pump installations.

MCS (Microgeneration Certification Service)

MCS is a standards organisation that maintains and improves quality by certifying low-carbon energy technologies and contractors. They have strict rules to ensure that the heat pumps work to their specifications and are as energy efficient as possible.

Without MCS sign-off you will not be able to get the £7,500 grant after installation. They look after the following:

  • Choosing an installer

    In order to get the grant under the boiler upgrade scheme, you must use an MCS certified boiler.

  • Authority and consent

    Once chosen, an installer will need to submit an application for your property. Ofgem will then need to confirm the application, and choice of installer with you. Consent is requested to stop fraudulent claims of the grant.

    This application does not mean you have committed to using this installer or installing a heat pump.

  • Approval and payment of the grant

    Your installer will have 3 months from approval of application to completing the installation. If this deadline is missed, another application will need to be submitted. Once complete the installer will apply for the grant for you.

Your Installers Responsibilities

The scheme is installer-led and aims to simplify the process for property owners. This means that your selected installer will handle various tasks for you, including:

  • Submitting a BUS (boiler upgrade scheme) application for you
  • Liaise with Ofgem on most matters related to the scheme
  • Informing Ofgem upon the completion of your heating system installation
  • Requesting the grant funds from Ofgem at the project’s conclusion

The grant amount should be subtracted from your initial quote, and it’s normally the installer’s responsibility to extend the discount from the BUS grant to you as the property owner.

Home Requirements

Air source heat pumps run at lower temperatures than traditional gas, LPG or oil boilers. This keeps them highly efficient. But it means you may not be used to the slightly different way the system works day-to-day.

Heat Loss Survey

The heat loss survey aims to gather all necessary information to design an efficient and cost-effective heat pump system tailored to your property. During a heat pump survey, the surveyor will focus on several key areas:

  • Detailed Measurements

    A room-by-room heat-loss assessment will be conducted, including measurements of rooms, windows, and radiators.

  • Heat Pump Placement

    The best location for the outdoor heat pump unit will be determined.

  • Mounting Options

    Advice will be given on whether a floor or wall-mounted heat pump is more suitable.

  • Hot Water Cylinder

    The existing hot water cylinder will be assessed for compatibility with the new system, and if none exists, recommendations will be made for installation and cost.

  • System Layout

    Data will be collected to design the heating system, including the need for radiator upgrades, as heat pumps may require larger radiators for efficiency.

  • Settings and Configurations

    Flow temperature and settings will be discussed, as they can affect the size and cost of the heat pump.

  • Electricity Load

    The electrical load and meters will be reviewed for compatibility with the heat pump.

  • Sound Assessment

    A noise test will be conducted to ensure the heat pump’s noise level is below 42dB when measured from a metre away from the nearest neighbour’s door or window.

  • Special Requirements

    Any unique needs, such as Solar Thermal or underfloor heating, will be considered.

  • Payment Options

    Information on payment methods and government grants like the Boiler Upgrade Scheme will be provided.

viessmann air source heat pump internal and external parts

Both parts of the Viessmann Vitodens 150-A Heat Pump System

EPC rating

An Energy Performance Certificate (EPC) provides details on a property’s energy consumption and offers suggestions for reducing energy use and costs giving a ‘potential’ score. It is mandatory whenever a property is bought, sold, or rented.

Before approving any grant applications, the property’s EPC is verified to ensure it was issued within the last decade and contains no recommendations for loft or cavity wall insulation. EPC reports are not checked for eligible self-builds.

If there are any recommendations for loft or cavity wall insulation an air source heat pump won’t be eligible for the grant until this is sorted. Once sorted, you can get another EPC survey completed and submitted. This new EPC report must not then have insulation recommendations.

Check your EPC here >


In order to get the heat from the heat pump into and around your home the system needs to pump a high flow of water at approximately 40 degrees centigrade. This is otherwise known as Delta 40.

To allow this high flow around the system you will need to have at least 15mm into and between all the radiators and 22mm pipe from the heat pump itself. This means that if you have 10mm pipes feeding any of your radiators you will need to upgrade those pipe runs for as long as they’re 10mm.

The cost of a whole-house repipe depends on a lot of factors like the size of your house and where the pipes run. It could range from approximately £4,000 to £12,000. Of course you may not need a whole-house repipe.


Alongside the pipes needing to be thicker, you may need chunkier radiators in order to allow heat into the room.

A lot of people will have seen, or know about the double panel double fin radiators, also known as Type 22. In older, less insulated properties you may also need to replace these with larger, triple panel triple fin radiators that will work with the lower temperature water.

Other additions

As already discussed, you will also need a hot water cylinder for your hot water taps and shower(s). If you already have one, the survey will note if it’s compatible. If it’s not then you will need a new one. If you don’t have one, maybe because you currently have a combi boiler, space will need to be made available. Ideally as close to the air source heat pump as possible.

If the external heat pump unit is not being wall-mounted it will require a solid base to sit on. This may require a concrete pad or something sturdy to hold it down to stop them becoming damaged.

Gaining Permission


You shouldn’t need planning for an air source heat pump. There is a section of the planning regulations or permitted development rights (PDRs) called ‘Class G’. According to Class G, you don’t need planning permission to install an air source heat pump on a house, bungalow, or block of flats. However, there are specific conditions and restrictions:

  • Volume and Number

    The pump’s volume is limited to 0.6 cubic metres, and you can only install one air source heat pump per building or within its curtilage.

  • Certification

    The air source heat pump must comply with the Microgeneration Certification Scheme (MCS) or equivalent standards. See the MCS section above.

  • Location Restrictions

    The pump must not be within 1 metre of the property’s curtilage, on a pitched roof, or within 1 metre of the edge of a flat roof.

  • Historical and Conservation Areas

    You can’t install the pump in a listed building or scheduled monument without further planning permission. In conservation areas or World Heritage Sites, the pump can’t be installed on an elevation that fronts a highway.

Distribution network operator (DNO)

DNOs are the companies who look after the physical network that transfers power and gas around the country.  There are a few of them, but they are not the company that you buy the power from. There are also a number of Independent DNOs who can work on the network too.

Why are we talking about DNOs? Because full air source heat pumps need authorisation from your region’s DNO in order to be installed, wired in, and turned on.

But, why? It’s to do with the Amp capacity of the network in your area. Some local networks could be chained (where power may come to your property but then go straight to your neighbour). Another issue is that the heat pump’s compressor can create ‘noise’ in the infrastructure, like an electrical vibration, which could affect people within the local network.

As we’re talking about amp capacity, you will need a 100A fuse for your home or heat pump circuit rather than the standard 60A…just something to think about.

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Frequently Asked Questions About Air Source Heat Pumps

The government grants are for £7,500 and can significantly reduce the initial installation costs. [Correct as of October 2023.]

If you’re considering home renovations or an extension, you’ll need to complete these changes before designing your heat pump system.

Major structural alterations can affect the heat loss and thermal performance of your property, which in turn impacts the heat pump’s efficiency and size requirements. Failing to account for these changes could result in a less efficient system that may not meet MCS standards, affecting your eligibility for government grants.

You will need to complete your extension or renovation and then get a new EPC report to show that you don’t need any changes to become an as efficient home as possible.

However, you can prepare your home for a future heat pump installation during the renovation process by considering the following:

  • Underfloor Heating/Radiators: Opt for underfloor heating or high-output radiators that are compatible with heat pumps.
  • Pipework: Ensure a minimum pipe size of 15mm for conventional heat pumps. Smaller pipes may require a customised system. 22mm pipes will be required from the heat pump itself, but this will be installed during the heat pump installation.
  • Space: Plan the locations for your outdoor heat pump and indoor water cylinder; the closer they are, the better. 
  • Insulation: Use the renovation as an opportunity to improve your home’s insulation, enhancing the efficiency of any heating system you choose.

All this depends on the actual make and model of the unit being installed. The external part of a heat pump has dimensions approximately 1m x 1m x 2m. Think about the rough size of an air conditioning unit. Some can require a metre of clearance on each side and in front for optimal airflow.

Indoors, you’ll need room for a hot water tank, which has dimensions of 2m x 1m x 1m, comparable to a contemporary fridge freezer. This tank can be situated on either the ground or first floor, ideally closer to the external unit for efficiency.

Contrary to this belief, our meticulous home surveys ensure that the heat pump system we install is tailored to your home’s needs. Unlike gas boilers, which can cause temperature fluctuations, heat pumps maintain a consistent, cosy temperature without incurring extra costs. As long as your home is insulated well enough and the pipework and radiators can get the heat into the property.

Modern air source heat pumps can operate efficiently even at temperatures as low as -20°C. In countries like Norway, where cold weather is the norm, heat pumps are a common household feature. While they may consume slightly more energy in extreme cold, they still outperform gas boilers in efficiency.

The compressor, the main engine of a heat pump, is regulated to operate within 40-60 decibels at a one-metre distance. This is comparable to the noise level of a fridge freezer or a gas boiler, and since the unit is located outdoors and mainly used on colder days, it’s generally unnoticeable.

Heat pumps are built to last as long as possible, nearly double the lifespan of a typical boiler, and they require less expensive upkeep. Installations come with a multi-year warranty (the length depends on the manufacturer) for the heat pump (subject to annual servicing) and a warranty for hot water tanks and radiators.

If you don’t want to get the grant of £7,500 from the government you could do pretty much what you like. You will still need DNO authorisation, but you could install it without the upgrades to pipes and radiators. But be aware, if not installed correctly it may need to work a lot harder than it should for maximum efficiency. This means it will cost a lot more to run and it’s lifespan could be affected.

We understand that there are a lot of hoops to jump through. But as it’s tax payers money it needs to be treated correctly. The grant scheme is very strict and if you don’t adhere to their rules you will not be eligible for the £7,500.

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