I am running one experiment and I can find quite interesting results. Fuel is mixture of many elements.
Take a look at the attached plot and data. Could you calculate COP from this?
Measurement was made by IR gun that logged the temperature. You have to just ignore step around 200 deg C. This is measurement error (wrong E) and apply for both plots.
In both runs everything was same except the red plot - reactor has no Hydrogen inside - vacuum. Next comparison must be done with Argon.
What you can see is basically 600W of applied power at the heater -- identical for both cases -- and the power was cut completely. Before cut the power was stabilized and temperature equilibrated.
You can see Heat after Death for 30 minutes. There was no insulation whatsoever but with some wool around it could last few times longer.