| Value | Category | 
                                    
                    
                        | 1 | Central heating | 
                                    
                    
                        | 2 | Electricity | 
                                    
                    
                        | 3 | Solid fuels (coal fire wood) | 
                                    
                    
                        | 4 | Gas | 
                                    
                    
                        | 5 | Liquid fuels | 
                                    
                    
                        | 6 | Combination: Electricity+ | 
                                    
                    
                        | 7 | Other combinations | 
                                    
                    
                        | 11 |  | 
                            
            Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.