## 4 Results and Discussion
### CO\({}_{2}\) Emissions for the Whole English Housing Stock  
Assuming that the 16,000 properties described in the EHCS are representative of the whole of the English housing stock, it is reasonable to extrapolate mean CO\({}_{2}\) emissions to the 22 million properties that currently exist in England, giving a baseline estimate of emissions of 112 Mt CO\({}_{2}\). Assuming this and the other assumptions described in Section 3.3, a series of scenarios have been modelled with the results detailed in Table 7 and summarised in Figures 7 and 8. For the current electricity grid CO\({}_{2}\) emission intensity, it is evident that at a heat pump penetration level of 55%, heat pumps performing at a mean CoP of 450% will realise an emissions reduction of 33%. With the penetration level increased to 75%, the emissions reduction increases to 38%. At the same grid emissions level and heat pumps operating at 250%, there is virtually no difference to the emissions reduction level of 17%-18% whether there is a 55% or 75% penetration level. At heat pump efficiencies of 200%, the reduction in emissions for 55% to 75% penetration levels is 8% and 3% respectively, _i.e._, there is a smaller reduction in emissions with a greater level of heat pump \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & & & **Total Annual CO\({}_{2}\)** & **Relative Reduction** \\
**Description** & **Grid Emission** & **Heating Technology** & **Emissions From** & **in Emissions** \\
**Intensitya** & **Mixb** & **English Households** & **Compared with** \\  & & & **(Mt)** & **Baseline** \\ \hline Only Gas & Current & 100\% B76 & 99 & - \\ Current Baseline Mix & Current & 85\% B76:15\% R & 112 & Baseline \\ HP COP 2.0, 55\% Pen & Current & 45\% B76:55\% HP2 & 103 & 8\% \\ HP COP 2.5, 55\% Pen & Current & 45\% B76:55\% HP2.5 & 92 & 18\% \\ HP COP 4.5, 55\% Pen & Current & 45\% B76:55\% HP4.5 & 75 & 33\% \\ HP COP 2.0, 75\% Pen & Current & 25\% B76:75\% HP2 & 108 & 3\% \\ HP COP 2.5, 75\% Pen & Current & 25\% B76:75\% HP2.5 & 93 & 17\% \\ HP COP 4.5, 75\% Pen & Current & 25\% B76:75\% HP4.5 & 69 & 38\% \\ Current Heating Mix & 2030 & 85\% B93:15\% R & 59 & 47\% \\ HP COP 2.0, 55\% Pen & 2030 & 45\% B93:55\% HP2 & 36 & 68\% \\ HP COP 2.5, 55\% Pen & 2030 & 45\% B93:55\% HP2.5 & 35 & 69\% \\ HP COP 4.5, 55\% Pen & 2030 & 45\% B93:55\% HP4.5 & 33 & 71\% \\ HP COP 2.0, 75\% Pen & 2030 & 25\% B93:75\% HP2 & 24 & 78\% \\ HP COP 2.5, 75\% Pen & 2030 & 25\% B93:75\% HP2.5 & 23 & 79\% \\ HP COP 4.5, 75\% Pen & 2030 & 25\% B93:75\% HP4.5 & 21 & 81\% \\ \hline \hline \end{tabular}  
* See Table 2 for grid emissions intensity; b B76 = Gas Boiler with mean efficiency of 76%, B93 = Gas Boiler with mean efficiency of 93%, R = Resistive Heating at 100% efficiency, HP2 = Heat Pump at COP of 2 (200% efficiency), HP2.5 = Heat Pump at COP of 2.5 (250% efficiency), _etc._ An increase in gas boiler efficiency is assumed for 2030 given increasing performance standards within the UK regulatory framework.  
\end{table} 
Table 7: Total estimated English household CO\({}_{2}\) emissions for different technology performance and penetration levels at current and aspirational electricity grid emission intensities. penetration. This anomaly for heat pumps operating at 200% is due to the smaller percentage of efficient gas boilers (93% efficiency in 2030) with a significant increase in relatively poor performing electrical heating systems within a high emissions grid. Thus, it can be seen that given the current emission factor ratio for electricity and gas respectively (2.78), for households currently heated by efficient gas boilers, only heat pump CoPs greater than 2.78 will deliver reduced GHG emissions for households. With a dramatic reduction in the electricity grid emissions intensity, Figure 7 shows that at a heat pump penetration level of 55%, heat pumps performing at 450% will now realise an emissions reduction of 71%.