WARM UP WITH SIZE MATTERS HEAT PUMP SYSTEM DESIGN SOLUTIONS
Detailed Heat Loss Site Survey
Heat Emitter Sizing and Selection
Detailed Heat Loss Site Survey
The heat pump survey involves measuring every room to be heated including windows, what the building is constructed from, all insulation types in walls, floors and ceilings.
Review the existing heating system - details, size and type of existing boiler, size of the existing radiators, size and design of the existing pipe work. It is vital this is carried with great care and accurate details are recorded to be able to undertake a heat loss calculation and heat pump design.
System Design
Heat Emitter Sizing and Selection
Detailed Heat Loss Site Survey
SiZe Matters heat pump system design is in accordance with recognised industry standards and guidance - MCS MIS 3005-D Heat Pump Design and CIBSE Domestic Heating Compliance Guide
Heat Emitter Sizing and Selection
Heat Emitter Sizing and Selection
Analysis of energy use - providing estimates of running cost and estimated savings
When installing an air source heat pump, the use of existing radiators can be problematic without careful consideration. Correctly specifying the heat emitters, be they convector radiators or Underfloor Heating (UFH) circuits, against the calculated room heat losses for given operating conditions is crucial to ensuring correct heating performance.
Analysis of energy use - providing estimates of running cost and estimated savings
Analysis of energy use - providing estimates of running cost and estimated savings
Analysis of energy use - providing estimates of running cost and estimated savings
While electricity is more expensive than gas, air source heat pumps benefit from exceptional average efficiency rates of around 300%. If that doesn’t sound impressive, we don’t know what will.
There is a range of cost-affecting factors that can shape the price of running an air source heat pump.
Heat Pump Efficiency
Naturally, the more efficient a heat pump is (or the higher its Coefficient of Performance (COP) is), the cheaper it will be to run. There are many highly efficient air source heat pumps on the market. Nonetheless, the heat pump variations from model to model are important when considering what your specific running costs will be after an installation.
Heating Demand
Obviously, the more energy you require from your air source heat pump, the more it will cost to run. What’s more, your home’s heating demand will be linked to the power of your heat pump.
So it may not necessarily be the case that you’ll end up running your heat pump more than a household with a lower heating demand but rather that you’ll be using a more powerful heat pump to meet your demand. Either way, higher heating demand is very much correlated with a higher running cost.
Household and Property Insulation
While heat demand is a key factor, how much heat demand will shape your overall running costs will in turn be affected by how well your home can keep the heat in. In the end, the goal is to heat your house only, not your neighbor's as well.
Heat Pump and Hot Water Cylinder Sizing and Selection
Analysis of energy use - providing estimates of running cost and estimated savings
Heat Pump and Hot Water Cylinder Sizing and Selection
Why does heat pump size matter?
You might be thinking the bigger the size of your air source heat pump, the better, right?
Well, not exactly. After all, you wouldn’t need an industrial sized gas boiler to heat a 2 bed house!
Air source heat pumps have a rating in kW, which represents their output. For example, a 10 kW rating on a heat pump will mean it delivers 10 kW of heat (based on the outside "design" temperature). Most air source heat pumps range between 4 kW to 16 kW. As a general rule of thumb, the greater your whole house heating needs are, the more powerful you’ll need your air source heat pump.
What size hot water cylinder do you need?
Just as important as getting your heat pump sizing right, is making sure your hot water cylinder can meet your home’s demands. An unvented indirect hot water cylinder is essential for systems with an air source heat pump. That may sound complicated, but it just means that the cylinder has a coil in it which is heated by the air source heat pump. This coil then heats the water in the cylinder.
Generally speaking, a typical domestic household will use around 45 - 50 litres of water for every person. Again though, it’s not always so straightforward. The habits of the people in the household will also need to be considered.
Room by Room Heat Loss Calculations
Analysis of energy use - providing estimates of running cost and estimated savings
Heat Pump and Hot Water Cylinder Sizing and Selection
To meet the MCS heat pump standard MIS-3005-D, a heat pump needs to be sized correctly to meet the heat demand of the building.
The standard states that a heat loss calculation should be performed on the building in accordance with standard BS EN 12831:2021 Heating systems in buildings — Method for calculation of the design heat load
This standard specifies methods for calculating the design heat loss and the design heat load.
The BS EN 12831:2021 standard is a room by room heat loss calculation which differs from SAP 2012 which implements a dwelling wide heat loss calculation. The BS EN 12831 standard takes into account the U-values of internal walls and the heat loss or gain rate through each wall into the rooms either side. This is needed in order to work out the heat emitter sizing in each room so that the room temperatures are met. Without a room by room heat loss calculation it could be easy to under size radiators
Distribution Network Operator Notification
SiZe Matters Air Source Heat Pump Surveying and Heat Loss Calculation Service
When installing an air source heat pump the property owner is required to get permission from the District Network Operator (DNO) before making the connection. This is because the DNO, who are responsible for managing the electricity distribution network, need to check whether the local network can handle the additional load from a new heat pump installation. If you install a heat pump without permission, you could be forced to remove it.
DNO applications for existing electricity supplies are handled by the installer. When considering which heat pump partner to choose, this is an important factor to consider.
Navigating the DNO process can be a challenge, and it is a requirement of the MCS scheme to have the DNO permission in place for a heat pump installation.
Noise Assessment Calculation in accordance with MCS020
An air source heat pump generates noise, and it can operate during the night and day. As a result, it has the potential to cause significant adverse effects to people living nearby. Since December 2011 Permitted Development rights allow MCS approved heat pump installations without the need for planning consent.
The MCS020 Planning Standard ensures the proposed location of the air source heat pump outdoor unit has a noise level lower than 37 dB (A) and therefore would not require planning permission from the local authorities.
On the 29th May 2025 MCS updated the MCS 020 standard, splitting it into two sections: MCS 020 (a) for air source heat pumps and MCS 020 (b) for small wind turbines. This update simplifies compliance for installers and includes a revised calculation methodology for air source heat pumps.
Key changes in the updated MCS 020 (a) include:
Sound level assessment:
Sound levels are now assessed to 37 dB LAeq, 5mins, down from the previous 42 dB.
Emphasis on sound power levels:
The standard emphasizes using sound power levels rather than sound pressure levels for assessment.
Improved assessment for multiple ASHP installations:
The assessment process for multiple air source heat pump installations has been improved.
Clearer definitions and barrier reduction values:
Definitions of acoustic barriers and updated barrier reduction values have been provided.
Clarification of conditions:
The update clarifies what can and cannot be considered a solid barrier, how to determine the assessment position, what can and cannot be considered a reflective surface, and the definition of a habitable room.
MCS Product Directory:
MCS will hold the A-weighted sound power level for MCS certified products on the MCS Product Directory.
Implementation guidance:
MCS has issued implementation guidance for the updated MCS 020 (a).
Mandatory compliance:
Compliance with this update is mandatory for installers seeking to install air source heat pumps under Permitted Development from September 20, 2025.
Consultancy Service
No matter how simple or complex the question is, I can help. By listening first, I can understand your concerns and needs thoroughly. I can guide you through the entire project and advise on solutions that fit your needs.
As an expert with over a decade of experience, I can address fundamental questions and concerns about the technical and financial aspects of installing an air source heat pump.
With links to manufactures and industry bodies I can answer any questions you may have about government legislation, policy, initiatives, or funding.
The consultation begins with a 30-minute call to better understand your questions or concerns. Then, we can agree on how the consultancy will progress and indicate the ongoing fees.
