Looking again at the IR type heaters, I have used them before for commercial applications and they have been very effective, as someone mentioned usually controlled by a Pir or occupancy sensor.
The biggest complaint we use to get was on picking PC stations in cold warehouses, the pickers would stop by the station to swap code readers and get warm then feel colder when they went off picking again.
I can see the point raised above, of those Sat close to them will roast while the further away will feel little benefit.
I have seen fans on heating as
@Simon47 describes above installed in a church before, they had to get it all running an hour before it needed to be warm but once working did a good job, they also had heating pipes under the pews to add some upward warmth.
That was oil fired and was a reasonable system. Probably one of the better system I have seen installed in a church so far but not without limitations, if it was really cold for a few days you could feel it creeping into the building.
I think most of these buildings you have to use a variety of methods to heat various different areas within the building.
Some I go to have a right mix of sizes and shaped rooms that all present different challenges!