Enjay's Lepido turns greasy kitchen fumes into restaurant heating

Every restaurant kitchen vents enormous heat straight into the sky, and the reason is simple: the exhaust air is thick with grease and soot, which stick to the surfaces of ordinary heat exchangers and kill them. As Hamburg University of Technology thermodynamics professor Arne Speerfork explains in the BBC's report, that contamination is why hot air produced by cooking is simply pumped out of the building.

Enjay, a start-up from Malmö in southern Sweden, spent its early years on a different question: what if the exchanger were designed for dirty air? Its answer, Lepido, is bigger than a conventional unit and built so the grease and soot flow past the metal coils that transfer energy rather than onto them. The hot air then passes over pipes carrying cold water, warming it for use around the building.

The economics did the selling. A Burger King franchise in Malmö that piloted Lepido in 2016 saves the equivalent of about $16,000 a year in heating bills; Enjay co-founder Nils Lekeberg says an average restaurant can cut heating bills by up to 90% and its carbon footprint by 30 tonnes a year. After going on sale in 2018, Lepido spread to around 25 Burger King franchises across Sweden, Norway and Denmark, plus school and hotel kitchens across the Nordics and Benelux — and after the energy crisis, enquiries in early 2023 ran five times their level a year earlier.

Don't filter the grease — reshape and resize the exchanger so grease and soot flow past the coils, then use the recovered heat to warm the building's water.

Heat exchange is textbook industrial kit; kitchen grease was treated as a law of nature that made it impossible. Questioning that assumption opened a market every restaurant was literally venting.

The mechanism is honest physics, not marketing: particles pass the coils, heat still transfers, and the building's existing water system does the rest.

Payback inside two years means the purchase decision runs on arithmetic, not green sentiment — which is why a fast-food franchisee, not an eco pioneer, was the first customer.

When a contaminant fouls a classic solution, the fix is geometry, not filtration. Enjay designed around the grease instead of fighting it — and the industry's biggest waste became its cheapest heat.

Lepido is installed in around 25 Burger King franchises across Sweden, Norway and Denmark and in school and hotel kitchens across the Nordics and Benelux, with UK trials under way at a Burger King in Welwyn Garden City and Turtle Bay restaurants in Salford and Birmingham. A four-person British rival, Dext, developed a similar Dirty Air Heat Exchanger with Nando's, now in 14 restaurants — evidence the market Enjay spotted is real.