How to Build a No-Heat Home

The very title of this article causes more head-scratching and soul searching than any other aspect of self-build today. It’s an immensely attractive idea: insulate your house so well that you don’t need to heat it. But is it practical? Or even possible?

The short answer to these questions is— No. Not if you want to enjoy a warm and comfortable home throughout the year. But it’s a No with certain qualifications. You can get most of the way there – in fact, almost all of the way there – and the amount of heat you require to get that last mile is minimal by our accepted standards, and as a result you may be able to save money on not having a conventional central heating system.

So how do you do it? You need to work to a plan. Just adding extra insulation is not enough. The obvious model to work to is PassivHaus, regarded as the world’s most demanding low-energy standard. Typically, to build a PassivHaus, you need at least 300mm of insulation in your walls, even more in your roof, and almost as much under the floor. You need to fit triple glazing. And you need to build a house that is far more airtight than anything we have been used to building in this country — so airtight that it has to be fitted with a whole house mechanical ventilation system with heat recovery (MVHR).

By doing all this (and more — there are various additional features you need to take into account), you find that normal everyday activities like breathing in and out,cooking, washing, watching TV and running computers generate almost enough heat to keep warm. Energy wonks call this‘incidental heat’, and it may contribute asmuch as 2kW of background heat,as long as people are occupying the house.

Now, the effect incidental heat has on the house depends very much on how it has been built. Take these three typical example houses:

• In an old pre-insulated house, it will lift the internal temperature by around 1°C

• In a house built to current Building Regulations (2006 version), it will lift the internal temperature by around 3°C

• But in a state-of-the-art massively insulated PassivHaus, it may lift temperatures by as much as 6°C. That’s enough to keep the house warm through most of the autumn and spring, when most people’s boilers are still powering away. And in the depths of winter, it means that you need far less energy for your space heating.

This energy saving can be expressed as a performance metric, which indicates the likely heat consumption in kWh per m² of internal floor area per annum — written kWh/m²/a. This metric is set to become the standard measurement of energy efficiency for homes in the future. This is how it looks on our three houses:

• Pre-insulated house: floor area 200m²; energy used for space heating 50,000kWh/a; performance 250kWh/m²/a

• Building Regulations 2006 house: floor area 200m²; energy used for space heating 12,000kWh/a; performance 60kWh/m²/a

• PassivHaus: floor area 200m²; energy used for space heating 3,000kWh/a; performance 15kWh/m²/a

Indeed, one of the things that defines a PassivHaus is that it should require no more than 15kWh/m2/a for space heating. But PassivHauses are not homes without heating: they are invariably fitted out with some form of space heating, though this is not normally a conventional central heating system. What PassivHaus builders usually do is add some form of heating element to the ventilation system, thus turning it into a warm-air heating system. This may consist of something like a 3kW heating coil, which is enough to take the chill off the coldest nights in winter and keep the whole house at a snug 18°C.

Is it possible to go beyond the PassivHaus standard and build homes that are heated entirely from incidental heat? In theory, it is possible to go further, but in practice insulation is subject to the law of diminishing returns and you would end up with walls and roofs so thick that you wouldn’t have much house left! In some climates, it is also possible to latch onto winter sunshine to make up the small additional heat demand with passive solar heating, but the problem in the UK is that the climate is too variable to make this a reliable heat source.So inevitably we fall back on having to use some form of additional space heating.

What is a PassivHaus?

It’s a standard – established by the PassivHaus Institut in Darmstadt, Germany, 1996 – for airtight homes insulated to a very high level, which allow the sun and other passive heat gains to produce enough energy to meet heating demands. See passivhaus.org.uk for more details or read more about it here.

Is Heating Cheating?

In recent years, many British selfbuilders have built homes that do without conventional heating, but few have gone as far as to build to PassivHaus standards. Instead, they opt to include some other form of energy-efficient heating, which is a perfectly acceptable compromise.

For example, Steve Lax and Christine Goddard built a 120m² house in Yorkshire in 2008 (BELOW), which they manage to keep warm in the depths of winter with little more than a 4kW wood stove as a heat source. The house is constructed using structural insulated panels (from SIPS@Clay in Skipton), which give a very highly insulated shell that is also inherently airtight.

Their heating and hot water strategy consists of: a 4kW wood - burning stove; an electric convector heater using a plug-in timer (for the odd 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 in the bathroom; and a mechanical ventilation system with heat recovery.

Steve comments: “On the whole, it’s all worked out just as planned. We have kept our wood stove going throughout the winter, and we’ve used just over 6,000kWh of electricity through the year — but only a very small fraction of this is used for space heating. In summer, the solar panel meets almost all of our hot water needs. The internal temperature never falls below 18°C.”

Read about three self-built houses without conventional heating systems...

Further reading:

• Passivhaus: The Last Word in Green Building?
• The Death of Central Heating
• SIPs: Faster, Greener, Warmer?