An opportunity to reduce rural carbon emissions

Switching rural homes to renewable heating can result in far greater carbon savings than doing the same for a townhouse. It's such a great opportunity, currently not being fully realised.   

That's because rural homes tend to be less well insulated, they tend to be detached, they can be harder to insulate, an so use more heat as a result.

They also tend to be heated by oil, whereas a townhouse will tend to be heated by gas. Oil has far higher CO2 emissions per kWh than gas, around 42% higher in fact.

Let's take two imaginary homes, one terraced townhouse on the gas network, the other a detached, stone walled, rural cottage (with a single phase electricity supply) heated by oil.

Both are near Birmingham.

Townhouse

Peak heat load 8kW

Yearly consumption 11,600kWh

CO2/kWh of gas = 0.21

Efficiency of the boiler 0.85

CO2 = (11,600 x 0.21)/0.85 = 2.87 tonnes.

Cottage

Peak heat load 20kW

Yearly consumption 34,380 kWh.

CO2/kWh of oil = 0.298

Efficiency of the boiler 0.85

CO2 = (34,380 x 0.298)/0.85 = 12.06 tonnes.

Let's swap both to renewable heating

The homeowners take advantage of the BUS (Boiler Upgrade Scheme) grant. The owner of the townhouse takes out their gas boiler and gets a heat pump installed. The owner of the cottage takes out their oil boiler and tank, and swaps to a wood pellet boiler.

The CO2/kWh for electricity is 0.136, and for wood pellets is 0.053

Let's assume that the townhouse owners got lucky and found a very good heat pump installer and as a result their seasonal efficiency is 3.5 - so for every kWh of electricity they use they get 3.5 kWh of heat. The CO2/kWh for the heat pump system is then 0.136/3.5 = 0.038 kg CO2/kWh.

Let's run those sums again:

Townhouse

CO2 = (11,600 x 0.038) = 0.44 tonnes

CO2 avoided per year = 2.43

CO2 avoided over 15 years = 36.45 tonnes

Cottage

Efficiency of the boiler 0.85

CO2 = (34,380 x 0.053)/0.85 = 2.1 tonnes.

CO2 avoided per year = 10 tonnes

CO2 avoided over 15 years = 150 tonnes

Value for money

Now let's look at the value for money we delivered in reducing CO2 emissions:

Townhouse

BUS grant £7,500

£205 per tonne of CO2 avoided

Cottage

BUS grant £5,000

£33 per tonne of CO2 avoided

If the cottage got the same £7,500 grant then the cost of the avoided carbon would go up to £50/tonne avoided.

Swapping the cottage to renewable heating in our example above is 6 times better value for money in terms of carbon savings, coming in at just 16% of the cost per tonne of CO2 avoided for the townhouse.

The Boiler Upgrade Scheme currently puts many rural homeowners, who have the greatest potential for carbon emissions reductions, at a disadvantage because they receive £2,500 less than if swapping to a heat pump were possible for them, which is a shame, and a missed opportunity. 

It would make good sense for the grant to be £7,500 in both instances. Even then the cottage is still great value for money, coming in at over 4 times the carbon avoided per grant-pound.