Your choice of system is not right.
For sewage pump station, you need to supply and exhaust air at 12 ACH while maintaining negative pressure with dual flow rates if you have gas and oxygen sensors and the like, see NFPA 820 ventilation chapter.
YOU need an Indeeco explosion proof duct mounted heater upstream of the supply fan.
Why go radiant when what you need is to heat the OA coming in, not the objects in the space.
How come your screen room is occupied? Screen rooms are seldom occupied, stinks like hell in there, one could pass out easily from exposure to excessive H2S if they stayed long periods in such an environment.
Read your NFPA 820 and stick to that, stop messing with your brain about system choice.