Deciding on your heating system
Tim Doherty shares what you need to know to get this crucial element of your new home right
Tim Doherty shares his expert knowledge to help you find the best central heating options to suit your new home
Main pic and inset: This new property didn’t have a mains gas connection, so the owners chose to install an underfloor heating system by Nu-heat (www. nu-heat.co.uk), powered by an air source heat pump. The heating manifold controls the flow of water to achieve the desired temperature
Finalising your new self build’s central heating system is an important decision that needs to be made at the start of your project. But who chooses what’s needed, what are the options and where should you start? Here’s what you need to know.
Fabric-first approach
The type and performance of your building envelope is crucial to the design of your heating system. You’ll probably have heard of the fabric-first approach, where building designers talk about extra grades and higher specifications of insulation and how airtight their detailing is proven to be. This really does matter, as reducing heat loss and air leakage should be one of the core design criteria for your space heating system.
A good example is the philosophy behind Passivhaus – another term you’re likely to have came across. The concept is to make the superstructure so airtight and well insulated that conventional heating systems are not required. In these buildings, everything from human activity to cooking and lighting contribute towards your space heating. There are accredited Passivhaus buildings in the UK and their owners are rightly very proud of the unbelievably low running costs they benefit from, so we know through published measurement that these principles really do work.
Mechanical ventilation & heat recovery
All buildings need ventilation. Stale air must be replaced with a fresh supply, plus smells, pollutants and moisture removed, too. In new builds we are required to create forced, controllable draught in our homes, the amount of which is dependent upon occupant numbers and household activity. The best way of achieving this, and central to the design of any energy efficient build, is the installation of a whole house mechanical heat recovery and ventilation (MVHR) system.
In these setups, the warmth in the outgoing stale air is recovered and transferred into the fresh, cooler incoming supply so little additional heating is required. In very simplistic terms, if your MVHR is operating at 75% efficiency and your space heating is set to 20°C, on a cold day (say 2-3°C), the new incoming air will be circulated at circa 15/16°C.
Comfortable living
Whoever is designing your heating system will need to know all about the building’s insulation and ventilation standards, as both will influence their calculations. But space heating is not only about adequate performance – it’s also about comfort and control, so the setup needs to suit your lifestyle.
Underfloor heating (UFH) is attractive for several reasons. First because it doesn’t get in the way of furniture and, second, as it provides an efficient and even heat distribution in each room. Other benefits include its compatibility with renewable tech, the fact it feels warm underfoot and its low maintenance requirements.
Radiators have a quick heat response time and tend to be cheaper to install than UFH, but tend to be reserved for areas such as bedrooms and bathrooms (eg as towel rails).
Whether you’re keen on very basic controls for your heating or embrace smart tech for an easier lifestyle. All options are available, but everyone involved in the system design will need to know your preferences.
Heat loss calculations
The first stage of your design will be the SAP (Standard Assessment
Procedure), which has to be carried out as part of your building control process. The SAP score is rated between 1-100+ and will confirm whether the project complies with current standards. This exercise is undertaken before your self build is constructed and it may be necessary to improve individual elements in order to pass. Space heating is only one component, but clearly must be adequate for each zone of the house.
The assessor will want to know the U-value performance (a measure of thermal efficiency) of your walls, windows, doors, floor and roof. They’ll also ask for the building’s orientation, amount of potential solar gain, proposed lighting and any intended renewable technologies, including heat recovery, heat pumps and solar panels. You’ll need to state what your primary heating source and fuel type for both space heating and hot water will be, as well as if there is any intended secondary supply, such as from a woodburning stove.
Who specifies the heating system?
The two key elements that need to be decided are the size and capacity of the individual room emitters (radiators, heated towel rails, underfloor heating or warm air ducts) and the boiler output, ensuring the fuel matches the information provided in the SAP.
It is unusual for an M&E (mechanical and electrical) engineer to get involved, as they usually confine themselves to commercial projects. Instead, the most likely candidate to design your boiler and emitters is a heating engineer or expert plumber. On occasion it could be carried out by the boiler manufacturer or radiator/ UFH suppliers, but this is fairly rare. MVHR is almost always designed by a specialist provider.
Whoever sizes the emitters and boiler will need to prepare heat loss calculations for each room. This takes into consideration the U-value of each building element (floor, wall, ceiling, roof, windows and doors), as well as the length, width and height of all fenestration. This will lead to what emitter sizes are needed, calculated in Watts. For example, on average a small room requires little more than 1kw of heat and larger rooms with more windows potentially 2kw-3kw.
The aggregate of this output, together with some capacity for the domestic hot water, will lead your engineer to the size of the proposed boiler. A 30kw boiler is quite adequate for an average sized property meeting current thermal standards.
Designing a renewable setup
Many homeowners will be choosing between an oil or gas boiler, with gas being infinitely preferable if a mains supply is available. Remember your heating engineer must be Gas Safe registered for gas installations and OFTEC registered for oil.
If you don’t want or can’t have a connection to mains gas, bottled gas or tanked oil, and instead intend on using a ground source (GSHP) or air source heat pump (ASHP) to fuel your underfloor heating, then the specialist manufacturer will need to design this system for you.
They will carry out the same heat loss calculations as above, but the sizing of their equipment is generally unfamiliar to most regular builders or heating engineers, so must form part of their package of services to you. Discussions can end up being quite complex, especially if you are liaising separately with the UFH supplier; for guaranteed performance, you may need to join these two firms together. Where heat pumps are involved for space heating, the domestic hot water is usually powered by electric immersion, perhaps being partly substituted with solar panels.
Another renewable option is a biomass boiler. This is another specialist product and can be unfamiliar to trades. However, the output should be rated in the same way as a gas or oil boiler, with the physical size of the unit being one of the most important criteria – this
is influenced by the fuel they burn, whether it’s logs, chips or pellets. The other key consideration with biomass is its controllability, as you can’t just switch the unit off and this usually means the design includes a heat sink of sorts. It’s specialist equipment and the design of all component parts must be carried out by the manufacturer.
Other options
Some folks still prefer electric space heating, using night storage heaters in key zones and thermostatically controlled panel heaters in others. This is the easiest (and generally the cheapest) form of installation and will be carried out by the electrician having been given emitter sizes by the heating engineer. But it isn’t efficient in use, so running costs will be high.
Warm air systems do not seem to be as popular as they once were and they require a considerable amount of ducting, which has to compete for space with any ventilation ducting being installed for fresh air supply.