Grant eco12/16 external wall hung. The Grant Eco wall hung oil-fired condensing boiler range includes four internal and four external high efficiency models. Ther boilers are available in 12-16kW and 16-21kW outputs in both system and open vented versions. These unique appliances are pre plumbed and encompass the patented Grant Vortex stainless steel heat exchanger.Internal wall hung models fit with Grant's EZ-Fit low level, high level and vertical flue systems, so almost any installation situation can be catered for. Grant Vortex Eco External wall hung models come with a factory fitted low level flue, robust external powder coated paint finish, built-in boiler frost protection, mains isolating switch and a test switch.