The Energy Company Obligation (ECO) works alongside the Green Deal. Under the ECO, energy companies with over 250,000 customers have an obligation (placed on them by Ofgem) to provide additional financial help for energy efficiency measures. For example, hard to treat cavity wall insulation may be the best energy efficiency option for a particular property – but may be cost prohibitive for the property’s owners. In these situations, the ECO can help homeowners realise their energy ambitions for efficient improvements.