Power supply to heating thermostats. Commercial building.

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

Reply to
Ignoramus21023
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I think if your thermostat uses power it'll require at least three conductors. Unless you can find a battery-powered thermostat?

nate

Reply to
Nate Nagel

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

Reply to
The Daring Dufas

Hi, Yes, if three leads coming into present 'stat for blower, heat, 24V AC control power lead, you can have programmable 'stat easily. Just make sure the 'stat you will get has enough wide range of temp. settings.

Reply to
Tony Hwang

No wiring needed. Programmable stat use batteries to power the clock but the same wires are all that is needed to make them work.

You will find that they have a minimum setting of 40 degrees. Yeah,

33 would save fuel, but 40 give a safety factor in case the heater break down.

I've had good experience with Honeywell and White-Rodgers. We have a couple dozen or so in our building.

Reply to
Ed Pawlowski

This is the crux of my question. Supposedly, some thermostats can charge their batteries from two 24v leads when not closing the contact, and use the battery when closing contacts.

i
Reply to
Ignoramus21023

I have only two leads.

i
Reply to
Ignoramus21023

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

Reply to
Ignoramus21023

And those, are two wire programmable thermostats with a battery? Right?

Reply to
Ignoramus21023

If you think it is costing you a lot of money on unnecessary heating just wait until you have a pipe burst when you try to save money by turning the heat down lower...

A setback to 38 degrees is too close to freezing considering that it might be colder further away from the thermostat location...

Reply to
Evan

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

Reply to
The Daring Dufas

-snip-

How's that going to work at 38-47F? I'm not sure if that will extend the battery life, or render it ineffective.

Jim

Reply to
Jim Elbrecht

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Take a look at any of the programmable thermostats at HD or online. Everyone that I've seen runs off batteries and will work with a simple two wire connection. Some will also use 24V, if available. Some also have an internal failsafe switch that will close at around 40 or so in case the batteries are dead. I'd check the min temp before you buy one. The ones I've had for sure will not go down into the 30's. Think

45 might be the lower limit.

And before going below 45, I'd consider where pipes that could freeze are located. For example if they are in outside walls, it's going to be substantially colder there than where the thermostat is located. When I've set back real low, like below 50, I make sure to leave open the cabinet doors under sinks that are on outside walls too so that it can get some more warm air in there.

Reply to
trader4

I doubt the batteries would work at -47°F but modern alkaline batteries don't seem to have a problem at 38°F at all. ^_^

TDD

Reply to
The Daring Dufas

I put a residential type Honeywell thermostat in my motor home. As there really isn't any 24 volts, AC, it runs off the internal batteries switching 12 volts DC. The batteries will last the entire summer season but may die sometime before doing the spring cleanup. Actually, sometimes they are still good in the spring. It sounds like your application is in a storage warehouse, or something similar. Is it possible to just use one thermostat at night, set to the low temp, to switch on and off the 24 volts to all the individual thermostats which are set to the higher temp? As we don't know the application and how critical the evenness of temperature is, this was just a light bulb idea.

Reply to
Art Todesco

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You can't find the time to reset them before leaving in the evening?

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Reply to
dpb

The nice part about programmable is reliability. No one forgets to turn them back, no one is chilly and pushes them up to 80. The ones in my shop are programmed and locked. You need a code to adjust them. That alone saves a bundles on energy.

Reply to
Ed Pawlowski

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You apparently missed the object of my posting, Ed. It was pointy-stick prodding only...

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Reply to
dpb

On 12/31/2011 11:57 PM, The Daring Dufas wrote: [snip]

One of the few things DST is good for. Set your clocks too.

Reply to
Mark Lloyd

I rather like DST (wish it were double) but the solstice is another good time.

Reply to
krw

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