Recuperators: Use waste heat from exhaust gases to preheat incoming air or gases, increasing combustion performance. Historically, market was focused on heat cascading (reusing heat) as the cheapest and simplest choice of heat delivery (Show 3). Heat pumps had been pricey and never capable of delivering temperatures over 100°C, and https://purethermal.co.uk/media-news/november-launch-waste-heat-recycling-design-support-service-from-pure-thermal-and-oilon/