if you're planning to do 6 separate tankless heaters for each unit you'd more than likely require main gas line upgrade. (biggerpockets.com)
The two main gases, methane and nitrous oxide, are considered to be more harmful than CO2 (methane is 21 times more powerful than CO2 and nitrous oxide is 310 times more powerful than CO2) so the data suggests that this is causing a highly dangerous situation for ourselves and, more importantly, for future generations. (meatfreemondays.com)
The next phase of the Energy Supplier ECO and the Warm Home Discount scheme must have a particular focus on those living off the main gas grid and in poor health where help is most urgently needed to avoid excess bills and excess winter mortality.» (politics.co.uk)