[quasse]

If you're still talking about electrical heaters here, there's literally no where for the energy used to go other than into heat for the room.

If you have two 1000w heaters, one made from a potato and ten clothes hangers and the other made from the highest quality materials known to man, they will still both heat a room the same amount.

Granted, one might have a better fan or more airflow and might therefore provide a more even heat distribution in the room, but they will both be providing the same amount of heat to the interior of the room. That's just how energy balances work. If 1000w is flowing from the plug into the heater and it's not being stored anywhere in the heater itself there's nowhere for it to go but into heat for the room.