## 3 Savings and Comparisons
### Estimates of Annual Gas Savings  
As energy efficiency becomes a central focus in building decarbonization strategies, upgrading household heating systems is gaining renewed importance across Europe. Natural gas boilers, still widely used in residential buildings, vary significantly in efficiency depending on their age, design, and technology [31; 32]. Older boilers often operate with efficiencies as low as 55%, resulting in substantial energy losses and higher operating costs. In contrast, modern condensing boilers can achieve efficiencies exceeding 90%, offering both economic and environmental advantages. Assessing the benefits of upgrading to a high-efficiency boiler requires a clear and quantitative understanding of fuel consumption and potential cost savings. This is particularly important for homeowners, policymakers, and energy advisors who aim to promote informed investment decisions and support climate targets. Standardized estimation procedures allow for consistent comparison of different boiler models, accounting for variables such as annual fuel use, fuel prices, and thermal efficiency. \begin{table}
\begin{tabular}{c c} \hline \hline
**SEDBUK (Seasonal Efficiency of Domestic** & **Energy-related Products (ErP)** \\
**Boilers in the UK) Efficiency Classes 2** & **Efficiency Classes 3** \\ \hline \hline \multicolumn{3}{c}{A++: 98\% and above} \\ A: 90\% and above & A++: 95\% to 98\% \\ B: 86\% to 90\% & A: 92\% to 95\% \\ C: 82\% to 86\% & A: 90\% to 92\% \\ D: 78\% to 82\% & B: 82\% to 90\% \\ E: 74\% to 78\% & C: 77\% to 82\% \\ F: 70\% to 74\% & D: 70\% to 77\% \\ G: Below 70\% & E: 65\% to 70\% \\ \multicolumn{3}{c}{F: 60\% to 65\%} \\ G: Below 60\% \\ \hline \hline \end{tabular} 1 Requirements are the same for new and existing buildings; only the way that the efficiency information is shown is different under the 2015 ErP Directive. 2 SEDBUK originally used a percentage-based system to indicate the efficiency of boilers, but it is now often presented as a letter rating, similar to energy-related products (ErP). 3 Since 2021, the current energy label with energy classes from A++ to D is gradually being replaced with a new, simpler scale from A (most efficient) to G (least efficient) [30].  
\end{table} 
Table 3: Energy efficiency class symbols 1. The following example outlines a step-by-step method for calculating the annual gas and cost savings when replacing a low-efficiency boiler with a high-efficiency model. This approach not only illustrates the potential for household savings but also provides a framework for broader cost-benefit analyses in the residential heating sector. Steps to estimate gas savings include the following (example is for switching a 55% efficient boiler with a 95% efficient one):  
Determine annual fuel consumption of the current boiler: Find out the annual fuel consumption of your current boiler. This can be obtained from the gas bills or estimated based on heating needs. Assume the current boiler consumes 1260 m\({}^{3}\) of natural gas per year. Calculate the annual heating cost with the current boiler: Multiply the annual fuel consumption by the cost per cubic meter. For example, if the cost is around EUR 0.50/m\({}^{3}\)[11; 12], this gives EUR 630. 1. Calculate the effective heating output of the current boiler: Multiply the annual fuel consumption by the efficiency of the current boiler (55%, i.e., 0.55): 1260 m\({}^{3}\)\(\times\) 0.55 = 693 m\({}^{3}\);
2. Determine the required fuel consumption for the new boiler: Divide the effective heating output by the efficiency of the new boiler (95% i.e., 0.95): 693 m\({}^{3}\)/0.95 \(\approx\) 729.47 m\({}^{3}\). Calculate the annual heating cost with the new boiler: Multiply the required fuel consumption by the cost per cubic meter: 729.47 m\({}^{3}\)\(\times\) EUR 0.50/m\({}^{3}\)\(\approx\) EUR 364.74. Estimate the annual savings: Subtract the annual heating cost of the new boiler from the annual heating cost of the current boiler: EUR 630 - EUR 364.74 \(\approx\) EUR 265.26.