Подскажите, что это за нагреватели?

vertical up-fired and down-fired heaters

мне ничего другого в голову не приходит, кроме как огневые нагреватели с пламенем, направленным вверх/вниз. но в инете такого нет

Заранее спасибо!

In the down-fired heater, combustion gases generated in the radiant chamber pass downwards through a refractory checker hearth into a collecting chamber beneath. From there the flue gases flow upward through the convection section and then out to the stack. The down-fired heaters are basically intended to fire on heavy residual fuels, where the flue gases are corrosive and may clog flue gas passages of conventional heaters.

Convection sections are thus protected by removal of combustion solids and are usually provided with inspection ports, soot blowing devices and tube facilities to keep the coils clean. Burners in down-fired heaters are always mounted in the heater-end walls.