the (entrance way ) is the breaching from the boiler to the stack

these are FD (forced draft fans) they force the primary air threw the boiler along with the products of combustion threw the stack breaching and up and out the stack

in the power house where i work we record
Red- tempature
Purple- flow Gas
Green- flow steam
Blue- flow oil
and they have to be changed every 24 hours

i have 3 york chillers in my boiler room and On December 9, 2005, YORK was acquired by Johnson Controls

you are correct it is used for respitory meassurements. its now caled a peak flow meter easly google it. most asthmatics use one every day and once every three months they have a lung capacity check

i remember when i wrote that the horid meories of that place the torture you went threw the friends that where just misunderstood or abused. the inicence taken from us why