heat questions on amps

i bought two small 40 watt solid statecombo amps- one for guitar, one for bass for home playing and small venue worship only.
1.the bass amp has grill at the back which shows the heat sink inside. is that enough to let the heat out or should i let a tech install a small fan?

2. the guitar amp has no grill, but the power supply (transformer) is exposed under the amp near in the speaker compartment. is that enough to let the heat out or should i let a tech install a small fan?

a friend said heat will cause an amp to burn up and fail.
thanks,

ldr

in theory, the designer of the amp should have solved any problems regarding heat and ventilation ... i wouldn't worry about it ...