I have a commercial building with about five thermostats for
heating. They are of the non-smart variety, maintaining the same
temperature regardless of time of day, with only a pair of 24v
contacts leading to them.

Given that it is a 10,000 square foot building, this is costing me a
lot of money spent on unnecessary heating during nighttime.

During the day, I want the temp to be 47 degrees, and at night, I
would be happy with 38 degrees or so.

Do programmable thermostats need a separate power supply, or can they
run themselves from just a pair of 24v wires that they open and close?

In other words, if I buy and install programmable thermostats, will I
have to run any additional wiring?

Thanks
i