The range cooker wasn’t intended for modern homes — and must be planned for in the design of one. Our guide explains whether an aga (or range cooker) can run central heating, the design principles behind them as well as a look at different models and sizes of Agas, Rayburns.

The main problem in the relationship between a modern house and an Aga – or other cast iron range – is that a modern house is, by design and regulation, thermally efficient. It is good at retaining heat and needs relatively little to heat it. A 200m² floor area house built to current Building Regulations standards will need 11,000kWh of space heating energy across the year. With the new Regulations planned for 2013, that figure is likely to drop to around 9,000kWh.

The Aga, on the other hand, first came to the market in the 1920s and was designed to deal with large, old, draughty 19th century houses. The design and efficiency of the Aga has changed since then but the technology is still from a different age.

(MORE: Buyer’s Guide to Range Cookers)

According to Aga, its electric cooker with ‘intelligent management system’ (called AIMS) consumes 190kWh per week. That is 9,984kWh a year and most of that energy is emitted to the house as heat. A two-oven gas-fired Aga with AIMS consumes 17,680kWh per year and a four-oven oil-fired model, for which AIMS is not available, will use 28,000kWh. A good deal of that heat will disappear up the flue but some 10,500kWh and 17,000kWh respectively will be emitted to the house.

In winter, our 200m² house will need around 280kWh of heat per week (it will vary with the outside air temperature) and then the electric Aga with AIMS is making a useful contribution — but even a two-oven oil-fired Aga could meet the whole of that demand on its own. Unfortunately it will still put out that same amount of heat in summer. In the case of the AIMS-equipped Aga, it is fairly short term – like a traditional cooker – and we have learned to cope with that. But the heat storage models are more of a problem as they put out heat all day, every day.

The solution lies in design and calculation. If we assume that the Aga is an essential part the design, then the house has to be designed around it. There is a relationship between the Aga, the size of the house and the level of insulation, and they have to be brought into balance.

A new build is controlled by Building Regulations, so we have to achieve a given level of thermal efficiency. Currently that equates, very broadly, to a maximum space heating energy consumption of 55kWh per m² floor area per year — so a 200m² house will need 11,000kWh of heat. All but electric Agas put out more heat than the house needs.

Designing an open plan living area that allows the heat from the Aga to circulate naturally from, say, the kitchen to dining room and family room makes obvious sense. As does designing in stairwells, atriums and internal balconies that allow ground floor air to circulate to the first floor. But there will still be a need for another heat source. The Aga produces low-grade, background heat spread across the day rather than the shorter-term, higher temperatures that a normal occupancy pattern wants.

Heat recovery ventilation also helps move the heat around the house and will be effective in spring and early autumn. But it will not be enough to heat the lounge or bedrooms in winter and a boiler and heating distribution system will be needed.

For refurbishments or a very large new build there may be a bit more flexibility. If the preference is for a gas- or oil-fired Aga then the actual heat output to the house needs to be calculated, as it will vary with the size of the Aga and the fuel. Then it is a matter of designing the insulation and, more importantly, the airtightness to suit. There will still be minimum standards to meet but a low airtightness figure (15m³/hr perhaps) will provide greater air movement and allow some of that excess heat to be dissipated — essentially reverting the design towards the 19th century draughty country pile the Aga was designed for.

In this situation, moving to the Rayburn Heatmaster may be an option. A couple of Aga models will provide domestic hot water as well but the Rayburn can be the primary heat source, running central heating and domestic hot water from a back boiler. This range can also run on wood fuel — a bit of a nuisance perhaps but cheap to run and carbon neutral. Generally using these machines to heat water is a poor idea given their inherent inefficiency when compared to a modern boiler, but if the Rayburn is going in anyway…

Happily the Aga is ignored in SAP assessments as it is a cooker (the Rayburn is assessed as it is a primary heat source), which may be just as well given the CO₂ emissions. An electric Aga will produce some 5.9 tonnes of CO₂ per year versus 1.9 tonnes for a gas boiler producing the same amount of heat.

So can you live with an Aga in a modern home? The answer is yes, but it is a matter of picking the right Aga for the house. The Aga Total Control range operates in almost the same way as a conventional cooker so the waste heat emitted to the house is minimised. The older Aga can be upgraded to become programmable like the Total Control range.

But this all ignores the running costs, which will vary from around £800 per year for the smallest gas-fired model with AIMS to around £1,700 per year for the largest oil-fired cooker without AIMS, with electric Agas somewhere in the middle. But the Aga is a lifestyle choice and running costs have to be irrelevant. A bit like the Rolls Royce, if you have to ask how much it costs to run, you can’t afford to run it.

(MORE: Buyer’s Guide to Built-in Ovens)

What exactly is an ‘Aga’?

The difference between the modern Aga and a conventional cooker is largely in the eye of the beholder, but essentially an Aga is a cooker — unlike a Rayburn, which is a cooker with a back boiler, able to drive some radiators and provide domestic hot water. Some Agas can deliver hot water but they are still essentially cookers.

The classic Aga and Rayburn operate by running 24/7 and provide slow or fast cooking options to ovens and hob. The Aga Total Control and iTotal Control ranges can be switched on and off at will – just like a cooker – and do not store (or emit) heat in the same way as the classic Aga.

While the name ‘Aga’ has become virtually a generic term for traditional cast iron range cookers (a bit like ‘hoovers’), there are a number of competitor companies producing quality ranges in a similar style — and they don’t necessarily appreciate the comparison.

The Least You Should Know

  • A traditional heat-storage Aga is on 24/7 and emits heat, so the house has to be designed to suit. Some newer models may be switched on and off as needed.
  • An Aga with a back boiler, called a Rayburn, provides central heating and domestic hot water.

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