Where exactly can you see "Heat" stat?
Click the Whiteboard link at your house.
It doesn't show the exact percentage, but says stuff like "It's very cold outside" or "It's getting warm."
There's also the walkie-talkie icon in the lower left corner of the screen. It changes color from blue to yellow to red depending on how much heat you've got.
I once sold about 40 drug shipments to the Distributor at once and got something like 300-400 heat from it, but there was no instant arrest or anything. The icon turned red and there were signs of increased surveillance all over the different districts, but I got home and went to bed and the heat dropped just fine. The 404 Bleach service helped there too.