The Death of Central Heating?

For the past couple of years, the PassivHaus has been the buzz concept in housebuilding. Hailing from Germany, PassivHaus is a performance standard for both new and refurbished homes, which is so exacting that you no longer require a central heating system to keep warm. Instead, the heat load is designed to be met by the incidental heat given off by the people living in the house and the electrical appliances. That’s not to say that a PassivHaus has no heating at all: generally they are fitted with radiators in the bathrooms and also with small booster heaters, sometimes powered by air-source heat pumps, on their ventilation systems, but these are generally used in only the coldest of weather.

If there is one criticism of the PassivHaus standard it is that it is incredibly demanding to build. The houses are cocooned in a 300- 400mm blanket of insulation, and the levels of airtightness demanded are more exacting than anything yet achieved in the UK.

But there are lots of homes now being built in Britain which also dispense with conventional central heating systems, but which fall some way short of the insulation/airtightness levels demanded by PassivHaus. One reason for this is that our climate is comparatively mild. In Bavaria, they design their heating systems to be able to cope with temperatures as low as -15°C; in the UK, our design temperatures vary from -1°C in southern England to -4°C in Scotland.

The examples I have come across have been built using SIPs (structural insulated panels) which is a construction system very similar to timber frame but with improved insulation and airtightness. That’s not to say that these homes could only be built with SIPs – in theory, any construction method is capable of delivering a low-energy house – but SIPs in particular sell themselves on being a relatively easy way to get a well-insulated, near-airtight structure.

Rather than having no heating system at all, these properties tend to be based around the idea of having a stove in the living room and then using a mechanical ventilation system to distribute the resulting heat around the rest of the house. These homes tend to have a few back-ups in place, such as electric convector heaters or even the odd fan heater, plus some form of additional heating in the bathrooms; but they have dispensed with the main part of a central heating system: the pipes and the radiators.

Steve Lax and Christine Goddard are Yorkshire self-builders who have gone down this route. Their 120m² SIPs house is heated by:

• a 4kW woodburning stove
• an electric convector heater using a plug-in timer (for cold mornings)
• an electric fan heater in the study
• a solar panel on the roof for summer hot water
• an immersion heater for winter hot water
• electric underfloor heating mats in the bathroom
• a mechanical ventilation system with heat recovery (MVHR)

What was their experience like over the first winter? Steve comments: “On the whole, it’s been great. We kept our small 4kW wood stove going throughout the winter and we burned a lot of logs — maybe five loads at £45 a time. In addition to this, we use a convector heater on a plug-in timer for a short while on the coldest of mornings and I have a fan heater in my study which, again, I only use for brief spells on the very coldest of days. We’ve used just over 6,000kWh of electricity through the year: well over half of this is accounted for by lighting, appliances and the various pumps we are running. All in all, over the winter we spent around £200 on logs, and about the same amount on electric heating for the hot water and the supplementary heaters. The internal temperature has never fallen below 18°C, despite it having been a pretty cold winter.”

Steve and Chris seem very happy with the performance so far. They have essentially heated their home with a wood stove, coupled with a whole-house ventilation system. Though it’s still some way short of the PassivHaus standard in terms of insulation, the overall primary energy use per square metre (which is how PassivHaus is measured) is within 20% of the PassivHaus target. That’s a good result, making it between 50-100% better than a house built to current Building Regulations.

But whilst these are homes without conventional central heating systems, they are not ‘homes without heating’. A 4kW woodburning stove may look ridiculously small, but it still consumes masses of logs during the winter months. And the resultant heat is being pumped around the house by the MVHR system, so there is still heat distribution taking place, even if it’s not radiators or underfloor heating. But the overall energy bill for Steve and Chris’ house is around £800 for the year (£600 electricity, £200 logs) which is something to shout about. So, in conclusion, it may be an exaggeration to state that central heating is dying — but low-energy living is certainly growing up.

The Stove in Question

Steve and Christine heat their home mainly by firing up this 4kW woodburning stove (PICTURED BELOW). They burned five loads last winter, at a cost of around £45 a time. Aside from this, they use electricity to supplement their home’s heating — utilising underfloor heating mats in the bathroom, an electric fan heater in the study and an electric converter heater on a plug-in timer. They estimate they spent around £400 over winter in heating costs. According to the UK Office of National Statistics, the average four bedroom house with a condensing boiler would cost £716 to heat over winter.

Greener Options for Heating Systems

There are more greener heating options than you might think. Biomass is one of the most popular options, with woodburning stoves (2) and biomass boilers (3) – which provide a greener central heating system – coming rapidly to the fore over the last year. For highly insulated houses, a single gas fire (4) could be all you need in the main living area to keep warm, or electric underfloor heating (3) in the bathroom will keep your feet toasty — either way you could forgo central heating. Renewable central heating options can be powered by solar (5) and ground-source heat pumps — which are an excellent way to power underfloor heating. Mechanical ventilation is already an essential component of super-airtight houses, so combined with heat recovery will provide both heating and cooling as and when you need it.

ABOVE: 1 & 2. Biomass boiler and Mozart woodburner from Euroheat; 3. Warmup® Foil Heater electric underfloor heating; 4. Gazco Riva gas fire; 5. Solar panels from Smart Solar

In Defence of Central Heating

Martyn Bridges, Director of Marketing and Technical Support at Worcester, Bosch Group, argues why central heating definitely isn’t – and shouldn’t be – dead.

“The case for cutting out a central heating system is certainly not for everyone, and, with the latest advances in heating technology, it needn’t be so. There is plenty that can be done to both new and existing properties to make the most of systems already installed and to harness free energy sources to increase efficiency, lessening their impact on the environment.

“For those wanting to renovate with an existing radiator system, something as simple as replacing an old, inefficient boiler over 15 years old with a new ‘A’- rated condensing boiler will see energy efficiency increase from around 50% (‘G’- rated or less), to over 90%, seeing savings of up to £275 a year in fuel (according to the Energy Saving Trust). “Upgrading controls to weather- or load-compensation models will additionally reduce the demand on the boiler and subsequent gas supply, effectively keeping the boiler temperature at a minimum yet maintaining a comfortable temperature.

“Renewable technology has also become a more accessible option. Solar remains one of the cheapest and easiest renewable technologies to install, and a solar water heating system really is an investment for both now and the future, giving instant savings on fluctuating fuel bills. The average household could see a reduction of around £65 on their annual fuel bills and around 325kg/CO2 (according to the Energy Saving Trust).

“In the same way Steve and Christine use solar energy to generate hot water in the summer months, going down the solar water system route means that more households around the country have the opportunity to switch their boiler controls off completely in the sunnier months, whilst still meeting all of their hot water needs for free.

“Other options, such as ground-source heat pumps and air-to-air and air-to-water heat pumps, are available to install now but will no doubt gain greater share going forward – particularly where new build is concerned – as we move towards a zero-carbon era.”

Visit worcester-bosch.co.uk or call 01905 752780.

Further reading:

• PassivHaus: The Last Word in Green Building?
• Are SIPs the Right Choice For Your Self Build?
• Choosing the Right Heating & Plumbing Systems for Your Self Build