For the record, cold blooded animals also produce heat as a byproduct of respiration and exertion, they just don't self regulate their temperature like warm blooded animals and as a result generally produce much less body heat.

They are also just as vulnerable to losing body heat if the room is cold. They don't "run warm" but they bask to raise their body temperature and lose that body heat to the air and the ground as they go about their day if their energy level is insufficient to make up for losses to the air. If snakes were comfortable being the same temperature as the air they wouldn't need to bask in the light.