On 12/31/2011 11:24 PM, Ignoramus21023 wrote:
On 2012-01-01, The Daring wrote:
On 12/31/2011 9:10 PM, Ignoramus21023 wrote:
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

Most electronic thermostats have a battery compartment for two AA or AAA
batteries with an option for powering the T-stat from the 24 volt supply
but you usually find more than 2 conductors in a thermostat cable. Most
thermostat cable has 5 wires colored white, red, green, blue and yellow.
Normally red is the hot wire with blue being ground or common. A
mechanical heat/cool thermostat will use all but the blue wire. A heat
only thermostat will use red and white but green will used if the fan
can be turned on without the heat. Unit heaters, the type you may see
hanging from the ceiling in a lot of warehouses are usually controlled
using only two conductor cable. A programmable thermostat can work with
a two wire system if you remember to change the batteries once a year.

TDD

If it is once a year or even once per quarter, I can live with it.

The batteries will more than likely last more than a year but like
battery powered smoke alarms, change the batteries with the change of
season or daylight savings time change.

TDD