Scottish Government

Chapter Four Energy Efficiency in the Home

4.1 The National Home Energy Rating ( NHER) score ¹⁸ provides a succinct measurement of the overall energy efficiency of a dwelling, through an assessment of its heating and hot water system or appliances and their controls and efficiency, as well as the ventilation factors and the insulation characteristics of the home. For any given size of dwelling, the lower the NHER score, the more expensive it will be to heat to standardised heating pattern. A NHER score of '0' indicates a poorly insulated dwelling that is reliant on an expensive form of heating, while a score of '10' indicates a dwelling that is extremely efficient in its overall use of energy. A dwelling built to the Part J heating and insulation standards of the 2002 Scottish Building Regulations typically scores between 8 and 10 on the NHER scale.

NHER Profile of Dwellings in Central Heating Programme

4.2 The detailed energy audit survey of every dwelling in this survey allowed a full NHER assessment to be completed on each dwelling using the NHER Surveyor 3 program. The overall NHER profile for the surveyed dwellings, comparing their NHER scores before and after the CHP improvements, is displayed in Figure 4.1. What is evident is the considerable increase in the NHER scores after the CHP improvements.

4.3 Prior to the CHP improvements, over 70% of all the dwellings surveyed (71.4%) scored less than 4 on the NHER scale (compared to 66.4% in the Year 1 sample, and 17% of all Scottish dwellings ¹⁹); while 89.7% scored less than 5 on the NHER scale ²⁰. The average NHER score of the Year 2 sample was 3.15 (compared to 3.31 for the Year 1 sample, and the Scottish average of 5.4 across all dwellings) ²¹.

4.4 This lower average NHER score is not surprising, as the general eligibility criteria for inclusion within the CHP (see Section 1.2) requires that dwellings do not have a central heating system. Heating is the single largest determinant of a dwelling's NHER score. Central heating systems can be significantly more efficient ²² to operate than individual room heaters (the minimum acceptable efficiency for boilers installed under the CHP is 78%, with some of those installed being rated at over 90%, compared to efficiencies of between 32 and 60% for most room heaters) ²³.

4.5 As a result of the CHP improvements, the average NHER score more than doubled, increasing from 3.15 to 6.67 (which is considerably above the Scottish average). With the new heating (and other improvements where installed), 39 dwellings (8.2%) still scored less than 4 on the NHER scale (compared to 26 dwellings (5.5%) in Year 1); and another 28 dwellings in the Year 2 sample scored 4 or better but less than 5 on the NHER scale. Further analysis of the dwellings scoring less than 4 and 5 on the NHER scale is set out below in sections 4.20 to 4.27.

4.6 Although the average increase in the rating was 3.52 on the NHER scale, the degree of impact varied considerably across the dwellings included in the survey. Figure 4.2 sets out the range of changes on the individual dwelling NHER scores as a result of the CHP improvements carried out. Over two-thirds of all the dwellings in Year 2 (68.2%) increased their NHER score by 3 or more points ²⁴.

NHER Profile by Tenure

4.7 The overall survey was disaggregated by household tenure - owner-occupiers, local authority, housing association and private rented - to examine the impact of the CHP improvements on the NHER profiles for these tenure groups within the sample population.

4.8 The average NHER scores for all four tenure groups, for both before and after the CHP works, are set out in Table 4.3. Comparisons of the range of before and after NHER scores across the different tenures are displayed in Figures 4.3 to 4.6 respectively. Considerable increases in NHER scores as a result of the improvements are quite evident across all four tenures.

4.9 Before the CHP improvements, the average NHER scores for all tenures were less than their respective Scottish median score ²⁵, reflecting the large number of low ratings in each tenure group (see Table 4.3). The percentage of the Year 2 dwellings scoring less than 5 on the NHER scale (that is, the SHQS standard that was introduced as part of the minimum energy efficiency standard for social housing landlords) ranged between 83.9% of the local authorities up to 92.7% of owner occupiers.

4.10 The Year 2 sample demonstrated a much wider range in NHER scores between the tenure groups than did the Year 1 sample. Prior to the CHP works, the average NHER score for the local authority dwellings was almost twice that for those in the private rented sector. In Year 1, there was less than a 5% spread between the highest (the owner-occupiers) and the lowest (housing association) average NHER score.

4.11 Subsequent to the CHP works, the percentage of dwellings scoring below 5 on the NHER scale ranged between only 7.1% of the local authority dwellings surveyed, up to 36.4% of the private rented properties. Despite the number of dwellings still achieving NHER scores of less than 5, all tenure groups achieved considerably higher NHER scores on average after the CHP works than Scottish dwellings generally.

Table 4.3: Average NHER Before and After CHP works: By Tenure

NHER Profile of Pensioner and Non-Pensioner Households

4.12 The overall survey was disaggregated by pensioner and non-pensioner households to examine the impact of the CHP improvements on the respective NHER scores. The considerable increase in NHER scores after the CHP improvements is quite evident for both groups when the before and after results are compared (see Figures 4.7 and 4.8 respectively).

4.13 The average NHER score for pensioner households was 3.08, while that for the non-pensioner households was slightly higher at 3.44 (see Table 4.4). Prior to the CHP improvements about 90% of the dwellings of both groups scored less than 5 on the NHER scale.

Table 4.4: Average NHER Before and After CHP works: By Age of Householder

4.14 As a result of the CHP improvements, the average NHER scores more than doubled for both groups: for pensioner dwellings the average NHER increased to 6.55, while non-pensioner dwellings increased to 7.16 (see Table 4.4). Despite these increases, 4.4% of non-pensioner dwellings households and 16.4% of pensioner dwellings scored less than 5 (see Table 4.4).

NHER Profile of Urban and Rural Households

4.15 The range of NHER scores was also disaggregated by rural and urban households, comparing both the before and after results (see Figures 4.9 and 4.10 respectively). Again, both groups show a considerable increase in their respective NHER scores as a result of the CHP improvements.

4.16 The average NHER score for urban households was 3.23, compared to 2.97 for rural households (see Table 4.5). Prior to the CHP improvements, 90.8% of the urban-based households and 87.8% of the rural ones scored less than 5 on the NHER scale (see Table 4.5).

Table 4.5: Average NHER Before and After CHP works: Urban and Rural Households

4.17 As a result of the CHP improvements, the average NHER scores more than doubled to 7.06 for urban households, and almost doubled to 5.79 for rural households. Dwellings scoring less than 5 on the NHER scale were significantly reduced to 7.3 % of urban dwellings and 17.6% of rural ones (see Table 4.5).

Combined Tenure, Age of Householder, and Locality

4.18 From the separate breakdown of the overall Year 2 sample by tenure, age of householders, and locality factors, the pensioner and owner occupier groups scored a mean NHER of less than 7, while the rural and private tenant groups scored a mean of less than 6. In contrast, the urban, non-pensioner, and the local authority and housing association tenant groups all scored a mean of above 7.

4.19 In Table 4.6, the before and after NHER results are disaggregated by the combination of all three of these factors ²⁶. It can be seen that the rural, pensioner, owner occupier group and the rural, pensioner, private tenant group account for the two groups with the lowest average NHER scores after the CHP works, as well as 61.2% of all the dwellings with a NHER score of less than 5.

Table 4.6: Mean NHER Before and After CHP works: By Tenure, Age of Householder, and Locality

Characteristics of Dwellings Still Scoring Less than 4 and 5 on the NHER Scale after CHP Improvements

4.20 While the tenure, age of householder and locality factors all have some effect on the low NHER scores achieved by some properties - 39 scoring less than 4 on the NHER scale and 67 in total scoring less than 5 - a more significant contributory factor here appears to be electric heating, or at least electric heating coupled with other factors. Of the 39 dwellings (8.2% of the sample) that still scored less than 4 on the NHER scale after the CHP works, all but one of these dwellings (97.4%) received an electric storage heating system under the CHP (see Figure 4.12). Of the dwellings scoring less than 5 on the NHER scale after the CHP works, electric storage heating was installed in 53 of the 67 dwellings (79.1%).

4.21 The mean NHER ratings of the dwellings, broken down by primary heating fuel are set out in Table 4.7. Dwellings with electric heating scored the second lowest NHER score on average before and the lowest NHER score on average after the CHP improvements.

4.22 In Year 2, electric heating accounted for 40.4% of all the primary heating systems before the CHP works, but accounted for more than half (52.2%) of the dwellings with the lowest NHER ratings ( i.e. those with a NHER of less than 4) overall (see Figure 4.11). Poor ratings for dwellings relying on direct acting electric heating appliances is understandable given the high cost of electricity charged on the standard tariff, but over 40% of these electric appliances (82 of 192) were electric storage heaters, using so called 'cheap rate' electricity.

Table 4.7: NHER scores by primary heating fuel: Before and after CHP improvements

4.23 Subsequent to the CHP improvements electric storage heating systems accounted for a fifth of all heating systems installed (21.1%) within the dwellings surveyed. However, even with the installation a new electric storage heating system the NHER achieved in more than a third of these dwellings (38 of 100) was less than 4 on scale. Subsequent to the CHP improvements, electric storage heating accounts for almost all of the lowest ratings.

4.24 Unlike Year 1, when electric heating accounts for a much larger percentage of the primary heating in dwellings in social tenure groups than in the two private sector groups, this was not the case in Year 2 (see Table 4.8). Many more owner occupiers in the Year 2 sample had some form of electric heating before and after the CHP improvements.

Table 4.8: Electric Heating by Tenure

4.25 While electric storage heating uses electricity charged on an off-peak tariff, which is cheaper than the standard rate tariff, it is still more expensive for a useful unit of heat than some other fuels. This price differential is exacerbated if electric storage heating is installed in dwellings with poor insulation characteristics, or other factors that will contribute to higher total heating costs, which will be reflected in lower NHER scores. Of the 38 dwellings with electrical storage heating that scored less than 4 on the NHER scale after the CHP improvements,

• 30 of the 38 (78.9%) have a wall construction that does not lend itself to an inexpensive insulation solution ( e.g. sandstone, solid concrete, and non-traditional constructions)
• 21 of the 38 (55.2%) were in rural areas where there was no mains gas supply at all
• 17 of the 38 (44.7%) were bungalows (the built form with the highest ratio of heat loss surface for a given floor area and volume)
• 12 of the 38 (31.6%) were bungalows with wall constructions that cannot be inexpensively insulated located in rural areas without a gas supply (and 8 of the 12 are detached bungalows). The one non-electrically heated dwelling scoring less than 4 on the NHER scale after the CHP works shared all of these characteristics as well.

4.26 Of the additional 27 dwellings that scored 4 or more but less than 5 on the NHER scale, 15 of them had electrical storage heating installed, 8 had oil central heating installed, and 5 had gas central heating. Electric storage heating was more prevalent in this group amongst the urban dwellings than in the rural properties, accounting for 9 of 11 urban dwellings compared to 6 of 17 rural dwellings). Breaking this group down further,

• 15 of the 27 (55.5%) have a wall construction that cannot be inexpensively insulated (8 with oil central heating, 5 with electric storage heating and 2 with gas systems)
• 14 of the 27 (51.9%) were in rural areas where there was no mains gas supply at all (8 with oil central heating and 6 with electric storage heating)
• 13 of the 27 (48.1%) were bungalows (of which 10 of the 13 were detached bungalows)
• 8 of the 27 (29.6%) were detached bungalows with wall constructions that could not be inexpensively insulated, located in rural areas without a gas supply. None of these 8 dwellings had electric storage heating installed under the CHP.

4.27 As can be seen in Figure 4.12, higher NHER ratings can be achieved with electric storage heating. However, in certain circumstances and dwellings, electric heating may not be the most appropriate heating system to specify. Other forms of heating may be more appropriate.

Overall Comments on Chapter Four

4.28 The overall impact of the CHP improvements is to considerably increase the energy efficiency of dwellings as reflected by the dwelling's NHER score. The consequence of this improvement is the likely reduction in the level of fuel expenditure required of those in these dwellings to achieve the satisfactory heating regime. The overall increase in NHER scores is mirrored in disaggregated data. This impact will be looked at more in Chapter 5.

4.29 However, in assessing the impact of the CHP programme on tackling fuel poverty, the issue is not the resultant NHER score, or how much the NHER score changes. However, low NHER scores are indicative of higher fuel bills.

4.30 Amongst the group of dwellings that are still achieving low NHER scores after the CHP improvements, there are a number of common characteristics: electric storage heating, walls constructions that are expensive to insulate, rural locations, a detached built form, and in particular, detached bungalows