I've lived near Cuyahoga County, OH for about 4 years or so, and I have extensively photographed most of the last remaining operational Thunderbolts in the county. If you know Cuyahoga County's CD System as far as the history goes, most of the Thunderbolts in the Greater Cleveland metro area were single-toned, 1000 models, branded by Federal Enterprises, and installed from 1951-1953. They featured the 6M series blowers on them. The Thunderbolts were all-roof mounted as far as I can tell. The three remaining units in the county (1 inactive, abandoned in place in Cleveland, two in operational service in Independence) are all-roof mounted. They are all jailbar grille units; consistent with the first few Thunderbolts that were ever installed. The old CD system also featured Federal Sign and Signal branded (as well as some Federal Signal Corp. branded) Model 5A/7A single toned omni-directional sirens, as well as more common 5AT/7AT dual-toned omni-directional sirens. The Model 5/7's and 5T/7T's were pole mounted for the most part; again the only last few units in operation are in Independence, and those are pole mounted, but the ones that used to be in Seven Hills (at least one of them) was mounted on the roof atop their FD (a 2001-130 on a pole now sits at that location; Seven Hills replaced those 5/7's in 2015). Anyways, on to the Thunderbolts: their BLOWERS are NOWHERE to be found. I've done some research, and since they indeed have blowers and they're not mounted on the roof with the siren head and the standpipe goes inside the buildings they are in, my most logical explanation at this time is to conclude they're mounted inside the building (because checking Google Maps confirms they aren't on the roof).
My question is: are there any other installations that were conducted in this manner, and were they common?
If you want to look at Google to see for yourself, the first Thunderbolt is on the Independence Service Center and the second Thunderbolt is on the roof of Mill and Motion Inc., a machine shop.