I am still not completely sure what they use them for. The locations I know of now are.
1. 5880 Woodway 77057 (Fire Station 2) Whelen 3016
2. T.C. Jester and Darling St. (Fire Station 11) Whelen 4004
3. 3100 Laura Koppe 77034 (Fire Station 34) Whelen 3016
4. Saturn Lane and Gemini (Fire Station 72) Whelen 4004
5. Gessner and Kempwood (Fire Station 77) Whelen 3016
6. 11236 Braesridge Drive (Fire Station 82) Whelen 4004
7. 911 F.M. 1959 77546 (Fire Station 93) Whelen 4004
8. 7409 Willowchase 77064 (Fire Station 96) Whelen 4004
Anybody know of any others

***UPDATE***
I went through the entire list of Houston fire stations on Google maps and found several more Whelens.
Here is the map link
http://maps.google.com/maps/ms?msid=207 ... 42eb&msa=0
While looking through the fire stations I also found a couple more Thunderbolt locations. Whether they are still there or not I do not know. I will try to make an old system map later on.