Conduction heat not balanced?

Nepal

Hi all,
I'm testing a conduction only case (no convection , no radiation), but the Heat added is not same as the solids gained!
my case is:
(dimension unit is INCH)
A solid(aluminum) cuboid 2x2x2 with 1x1x1 cuboid inside it. The small cuboid served as a heat source ,and now my condition and result shown below,<font color="blue">
1.) all solid initial temp= 0 degF, heat source (Total source) 20 Kg-m^2/S^-3(ie 20 watts), and simulation time=100 s.
2.) after run , I set the heat source as 0 watts and run it for steady state by using the previous result as initial result.
3.) the final solid temp=22.4683 degF </font>
and then I check the Heat added/gained are,
Qin=20 watts x 100 sec= <font color="red">2000 watts</font>
Qgained=M x Cp x dT
where M=Volume x Density=2 x 2 x 2 x (0.0254)^3 x 2702 =0.354223 Kg
Cp=903 [J kg^-1 K^-1]
dT=22.4683-0=22.4683 degF=12.4824 degC
So Qgained=0.354223 x 903 x 12.4824=<font color="red">3992.656 Watts</font> ?

Why I supply 2000 watts into the solid and I gained 3992 watts?
Is there something wrong with my calculation?