As a result of this experiment, we learned that we were not able to maintain the car’s inside temperature above 40 degrees overnight when the outside temperature was below freezing. During our best effort, the car still cooled to 30 degrees, only slightly above the outside temperature by dawn.

While we were not able to meet our goal, the data we collected offers a plethora of insights into the small, overnight environment of the car:

Questions and answers:

How much did we influence the temperature inside a car on the street at night using common insulating techniques that we learned from people who live in their cars? Using thermal mass?

We were able to significantly influence the car's inside temperature at the coldest time of night. Although the temperature in the car dropped to 30 degrees with our experimenter inside, hardly a habitable temperature, the temperature could have dropped as low as 17 degrees.

Using simple insulating techniques, we produced a difference in temperature of 7 degrees between the car and the outside, and the car maintained its heat for 4 hours, leaving 7 hours of night unprotected.

Using thermal mass, we produced a temperature difference of 16 degrees, and the car maintained its heat for 6 hours, leaving 3 hours of night unprotected.

How much of a difference does warmth from a person make in the environment of a car parked on the street at overnight?

With a person radiating heat, we produced a temperature difference of 24 degrees, and the car maintained its heat for all but 1.5 hours.

In general we noticed that a person warms the car's environment 6-10 degrees over a similarly-insulated car with no person.

Further study:

If we were to do this study again, we would better insulate the car's floor. We noticed during this study that no matter what changes we made to the car's environment, the floor remained significantly colder than the rest of the car, never reaching above 35 degrees.