I never had any problems with frost, apart from having to fire for heating! Remember that the Lancashire boilers were in steam all the time and even at winter shut-down you had hot brick settings, boiler and 7,000 gallons of hot water, all of which never really cooled down. When we eventually closed the mill Newton and I made sure there was anti freeze in the air pump and coffin bottom and drained all the other systems down. Even in derelict mills that had been closed down for many years, it took a very hard frost to penetrate the structure. Probably because they were so heavily built of brick and stone, different than modern portal frame and cladding structures. Only trace element heating I ever saw in a mill was on a black oil burner installation at Stainland. Problem there was that when the 'experts' went in to re-commision the boiler they assumed it was still on heavy oil when actually it was on 28 second oil. Result was a massive flue explosion when they pressed the red button after leaving the heaters on all night. Very embarrassing and quite a shock for them!
Hard frost at Bancroft in 1977.