energyefficientconversion.com

Doing some background research produces the following figures. In this case I’m quoting from Wikipedia, but the figures are corroborated across several well established sources.
“The housing stock in the United Kingdom is amongst the least energy efficient in Europe. In 2004, housing (including space heating, hot water, lighting, cooking, and appliances) accounted for 30.23% of all energy use in the UK (up from 25% in 1970 and 27.70% in 1990). The figure for London is higher at approximately 37%”
The use of domestic energy is split (in 2003) as follows…

• Space heating – 60.51% (57.61% in 1990)
• Water heating – 25.23% (25.23% in 1990)
• Appliances and lighting – 13.15% (13.4% in 1990)
• Cooking – 2.74% (3.76%)

Please read the rest of this Wikipedia article for lots of good detailed information, the link is on our Resources page.
Hence it is pretty clear that the priority order is now set out.

Space Heating

To reduce the space heating demand there are only four main choices…
1. Reduce the heat lost by improving insulation
2. Reduce the heat lost by preventing draughts (up to 30% of space heat can be lost this way)
3. Reduce the temperature difference to reduce the rate of heat loss
4. Install more efficient heating systems (e.g. condensing boiler) or swith to renewable (e.g. biomass/ wood pellet)

Domestic Hot Water (DHW) heating

To reduce the energy demand for DHW we can…
1. Use less hot water (shower, not bath)
2. Reduce the DHW temperature (to a limited extent this is worthwhile)
3. Heat it from a higher efficiency or renewable source

Appliances and lighting

For appliances ensure that all new appliances are rated “A” or “A+” for energy efficlincy. But beware of throwing out exiting serviceable units as new ones come with their energy of manufacture on toooo of th power one feeds into it.
For lighting switch to low energy lighting, notably fluorescent not incandescent lighting.

Cooking

The energy used here is really small copmpared to the others, so not much to do apart from being sensible and, when buying new, ensuring the appliances are “A” or “A+” rating.

What improvements can we realistically seek to achieve?

Great question! Let’s start from this figure from bvenergysaver…
“A typical household with gas central heating consumes about 23,000 kWh of total energy each year.”
Now let’s see the effect of applying it to the originally quoted case and applying some notional improvements…

For level 1 assume a reduction to 40% for space heating, 30% for DHW, 60% for appliances, 100% cooking, overall down to 42% of initial consumption.
For level 2 assume a reduction to 20% for space heating, 20% for DHW, 60% for appliances, 100% cooking, overall down to 28% of initial consumption.

Targets

Back to our question, are these improvements achievable? Well, for space heating they are if you are building from scratch using a standard like the Passivhaus standard. There the design goal is a space heating demand of 15kWh/m2/yr. So, for a two floor 3 bed house @ 150m2 that equates to 2,250kWh/m2/yr, not far from our figure in the last column in the table. However, to get to that level requires a significant attention to basic design, selection of specialist materials and fittings, and great attention to detail during construction. So Level 1 is more sensible for a cost effective refurbishment.
As for water heating, that level of annual replacement of gas or electric heating is achievable from the use of solar heating.
For appliances and lighting the modest reduction should be achievable through a combination of a switch to fluorescent/ compact fluorescent lighting, the use of A rated devices as and when replacement is needed and keeping an eye on consumption by switching off as many devices as possible when they are not in use.