Harold Kestenholz
I will rephrase your question to try to understand it in order to answer. You have 75 bathroom wall heaters that are made of copper tubes and something is lit, probably natural gas, by direct spark ignition or use of a match. There is no name plate on them so you can’t identify them therefore there is no serial number either.
Anyone who answers must guess at what this is. They might assume that there is no flue, so the units are in a small space without a chimney to vent the products of combustion. They could be radiant wall heaters with peizo-electric ignitors Like Empire Corcho 5000 btuh units. Perhaps someone in the world has seen something like this copper tube unit – or were there just pieces of copper tube that were supplied with the unit?.
You wish to replace them with heat lamps. This is fun trying to play Sherlock Holmes. I remember that Kelly Field was the name of an Air Force base near San Antonio, Texas where my grandfather designed the control tower.
I think it is illegal to install units without a nameplate and manufacturer rating approvals, so you might have something there as evidence of unsuitability.
