Hook up thermostat

Selecting the proper thermostat. If you are retired or if someone is at home during the day you likely do not need a programmable thermostat. If this is the case the only benefit you will get from a programmable thermostat or thermostats is at night. Or I prefer to say in the morning because you can set it so the unit comes on just before you wake. That way the house is at a comfortable temperature when you get out of bed. I will describe the advantages of the programmable thermostat in full detail in a different section below.

Once you have made the thermostat selection you can proceed to the next step. Helpful Page to help you select the right thermostat opens in a new window. Honeywell Thermostats Available Here. Thermostat Wiring and Installation Advisory………. If you decide to install your own thermostat you do so at your own risk.

There are many incidences where the homeowner installed their own thermostat and was successful. There are also many incidences where the homeowner was unsuccessful installing a new thermostat. The people that were unsuccessful wasted part of their day, ruined a thermostat or two and caused the malfunction of an integral part of their system.

Wiring Set-Up Explained

That is not mentioning the fact that they ended up calling a professional HVAC Technician to fix the problems. Problems caused by improperly installing a thermostat. The unsuccessful end up paying three to four times what they would have paid if a professional was called first. Factor this into your decision and if there is any doubt call a professional.

Call a professional to install and wire the new thermostat. Before you begin to install your new thermostat turn the power off. These are the four wires that you need to control the heat, cooling and the blower or fan.

This is for most air conditioning and heating systems. If the colors of the wires do not match the colors described here make sure you mark the wires with masking tape. Sometimes you will have extra wires that are not connected. Thermostat wire comes in many different varieties. The contractor who installed the system probably used 5 wire or 8 wire thermostat wire bundle.

They used what they needed and simply twisted or cut the other wires off. Thermostat wire terminations should be neat with no excess copper exposed. Additional answers to your questions concerning thermostats can be found here in our thermostat category index. Other questions about a Honeywell thermostat, Honeywell thermostats, programmable Honeywell thermostats can be found at the Honeywell Thermostat website.

Additionally, see thermostat wiring color code chart to help with How to Wire a Thermostat. This thermostat wiring diagram is a split system.

Wire A Thermostat

The wires going to the condensing unit are shown in red and white. However, these colors can be different. One wire originates from the thermostat Y terminal and terminates at the condenser. The other wire originates from the common side of the transformer. The transformer is commonly installed in the air handler.

In rare installations, the condensing unit will have the transformer. The manufacturer did not install the transformer in the condenser.

Choosing the Proper Gauge: 18 or 20

The transformer was blown in the past. Additionally, the colors here are typical. However, they can be different depending on who wired the unit and their color coding system. Most HVAC technicians will use this color code. However, there is an occasional oddball who knows better than everyone else. Or perhaps the wiring color combination was not available for the new installation. Always keep in mind to properly dispose of hazardous materials responsibly.

Older mechanical thermostats contain mercury and mercury are extremely hazardous to human health and our environment. Most municipalities have a hazardous waste collection site. They will be happy to accept your old thermostat and dispose of it properly.

Thermostat Wiring for Dummies

Additionally, there are state and federal laws that are explicit about properly disposing of hazardous waste including products containing mercury. Please do not throw the old thermostat in the regular waste bin. Be responsible and properly dispose of the old thermostat. See the About the Author page for information about the author of this article. Photo Uploads If you are human, leave this field blank.

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Honeywell Thermostat Wiring - Wire Programmable Thermostats - Heater Air Conditioner HVAC Furnace

Upload your photos or documents here! Drop a file here or click to upload Choose File Maximum upload size: Hello I would like to know how to wire two heating Units on a same thermostat. Becasuse i have these two heating units running on a same open space. Thank you in advance. We cannot use one thermostat to control two different heating system which were controlled by two different thermostat. You mentioned that some older tstats may have just an R and W wire, and therefore a new digital tstat may require new wire to be run a bundle containing a C wire.

My old tstat has simply a W and a C black wire. Do I need to run wire that has W, R and C? And if so, would it save me a headache to run a bundle with more wires in case I install an air conditioner in the future? C refers to Common in the 24 volt circuit and on the old mechanical thermostat I am not sure what the C stands for but you do need three wires and yes it would be better to run a bundle of more in case in the future you upgrade. I typically recommend that the two thermostats be combined into one thermostat that will handle both systems if in fact you do have a central air conditioner system.

Wire A Thermostat

With two different thermostats it is easy to have both systems running at the same time which is a waste of energy. You can pick up multiple bundled thermostat wire at your local hardware store. Ibought a new 18 seer 5 ton stright cool condensing unit and can not get it to run it has 2 stage heating and cooling can you help me thanks. If it is a 5 ton straight cool air conditioner then it does not have heat.

Straight cool means no heat, just cooling. If your thermostat does not have a Y1 and a Y2 then then you can stage it.

The Thermostat Wiring Color Code Guide

It needs a two stage themostat. Probably best to call an HVAC contractor to wire this for you. They can quickly identify what you have and wire it properly for control. I have a separate boiler and AC unit. I would like to install a new thermostat that is a WIFI unit. I can send photos of the boiler and the old thermostat wiring.

The wire running to the thermostat seams to be from the AC unit not the boiler. How should I wire the new thermostat.


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It is also possible you only have one thermostat. It really depends on how the system was installed and wired. Probably best to call a professional to hook this up for you as it is difficult to say without looking at the system you have and how it was wired. So, do I need to get a new one like that? Since I plan to replace it with the same type model..

Only thermostat like that that comes to mind is the old Honeywell T Honeywell does make a newer round digital thermostat.