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bephoto
New Member

USA
15 Posts

Posted - 11/16/2013 :  09:33:15 AM  Show Profile  Reply with Quote
Hey guys,

I visited this topic a little while ago, but am still a bit confuesed on the subject.

Specifically,

I'd like to install http://www.smarthome.com/2441TH/INSTEON-Thermostat/p.aspx for heat only.

I have open walls right now where I'd like to install these so i can re-run wire with no problem. Currently, there are 2 wires running to the thermostat, both connected to the T posts on my honeywell r845A.

I'm aware there is no C post in a honeywell r845A to power my thermostat so I will need the Venstar ACC0436 - two wire kit.

Here's where I get confused... I understand the idea of plugging the 24VAC adapter into the wall and being able to run power to the thermostat -- but where exactly would the 24v relay that is included in the kit go in my situation? in between the r845A and the thermostat, or somewhere inbetween the r845A and the furnace...?

Furthermore -- I've got 4 zones in my house, each with a thermostat I'd like to replace with an insteon thermostat -- is it possible to power more than one thermostat via one venstar 2 wire kit, or should I just purchase separate ones for each?

BLH
Advanced Member

5600 Posts

Posted - 11/16/2013 :  10:22:52 AM  Show Profile  Reply with Quote
Thermostat turns the relay On and Off. Relays output opens and closes the T Terminals on the R845A.
I believe someone here used a single heavier furnace control transformer and individual relays for the T connections on each zone.
As I don't think the wall wart AC supply in the two wire kit can handle too much extra load.

Edited by - BLH on 11/16/2013 10:24:40 AM
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stusviews
Moderator

USA
15603 Posts

Posted - 11/16/2013 :  12:30:42 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
The 2-wire kit cannot be used to supply power, only control. You need a 2-wire kit for each thermostat. With only two wires, you also need a power supply for each thermostat even though one power supply is adequate for all thermostats. Power consumption by a thermostat is negligible and you have only one furnace (best guess).

The wall are open. It'd cost considerably less to run new thermostat wire. You will need a minimum of three wires. If you run 18-5, then for a few dollars more you'll be prepared for possible upgrades.

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bephoto
New Member

USA
15 Posts

Posted - 11/17/2013 :  07:27:10 AM  Show Profile  Reply with Quote
Thanks guys-- still a couple follow up questions... The way things are run currently, with no insteon involved on a 2 wire system -- the thermostat essentially closes and opens the T connections on the r845A - correct? wouldn't a new powered thermostat do the same thing, and the only thing missing would be power to the thermostat? -- i.e. -- I'm not understanding the reasoning for a need for a relay in between the new thermostat and the r845a -- Isn't the r845A essentially just a relay and transformer in one.... with the 120v Relay being controlled by the low voltage T connections opening and closing...?

I'd just really like to fully understand how this works! :)

Also - since I'd like to power 4 thermostats eventually -- this idea of powering by way of a heavier furnace control transformer is intriguing -- anyone done this / can share insight into what they used and how it works. - --

And yes - 4 zone controllers r845a's on 1 furnace.

Already bought 18-5 thermostat wire, just need to figure out how to get power to the thermostat! :)
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BLH
Advanced Member

5600 Posts

Posted - 11/17/2013 :  09:58:38 AM  Show Profile  Reply with Quote
Here is a link to the Honeywell R845A data sheet with diagrams.
https://customer.honeywell.com/resources/techlit/TechLitDocuments/60-0000s/60-2481.pdf
One of the T terminals goes directly to its transformer.
Depending on which T terminal is on the R terminal of the 2441TH along with the one lead of the external supply for its power.
When you call for heat and R connects to W that is connected to the other T terminal.
You could get all kinds of strange voltages between the R and W connections.
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stusviews
Moderator

USA
15603 Posts

Posted - 11/17/2013 :  1:14:27 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
Info first
The 2-wire kit allows you to use/wire a thermostat with more functions when there are not enough wires for that added function, for example, when adding cooling to a system that has heat only. The included relay is to provide that added function. The relay independent of the rest of the HVAC system.

If you do not already have power at the thermostat, then, if you want a programmable thermostat, you must use an external power supply. The kit cannot be used to provide power from the existing power supply. At least three wires are required for that.

An single power supply can be used for many thermostats. Thermostats consume little power from that supply, none if it's a battery powered thermostat. Most of the load is the existing relay that controls the furnace and/or compressor. The thermostat is, basically, a temperature sensitive on/off switch. Switches, of themselves, use no power. For a thermostat, the power is for the display and programming. Minimal!

Two possible solutions
Run the 18/5 from each thermostat location to the zone control panel or get a 2-wire kit for each thermostat. Your choice

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bephoto
New Member

USA
15 Posts

Posted - 11/17/2013 :  11:18:55 PM  Show Profile  Reply with Quote
stusviews.... makes total sense. -- running 18/5 is not a problem -- but with the r845A not having a 24VAC post to run power -- I still need the external power supply - correct? -- So could I essentially run any 24VAC power supply in the furnace room and connect that to my 18/5 to run the power. -- something like this... http://www.homedepot.com/p/IQ-America-Multi-Voltage-Wired-Doorbell-Transformer-DT-1624A/202278728#.Uom_KRogfE0

Thanks for the help!

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stusviews
Moderator

USA
15603 Posts

Posted - 11/18/2013 :  1:10:08 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
If you have a thermostat, then the furnace most likely already has a 24VAC power supply.

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bephoto
New Member

USA
15 Posts

Posted - 11/18/2013 :  7:30:47 PM  Show Profile  Reply with Quote
just trying to figure out where it is then -- not in the r845A -- think I'll have an HVAC guy come in and wire one up for me -- then I'll just take his lead on the next 3!
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stusviews
Moderator

USA
15603 Posts

Posted - 11/18/2013 :  7:53:48 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
Most trades people are glad to show you what to do

BTW, do you have a zone panel?

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bephoto
New Member

USA
15 Posts

Posted - 11/19/2013 :  10:08:27 AM  Show Profile  Reply with Quote
not quite sure what that is... - I have 3 r845A's and one other similar device that runs both the furnace relays and a thermostat for a total of 4 temp zones. -- all r845a's and the other unit are connected to circulator pumps which send the hot water thru the house.

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stusviews
Moderator

USA
15603 Posts

Posted - 11/19/2013 :  10:55:12 AM  Show Profile  Visit stusviews's Homepage  Reply with Quote
The r845A is a relay with a 24V coil that switches 120VAC. Therefore, you do have a 24V power supply. The thermostats should be wired to control each relay independently.

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blckout20
Starting Member

2 Posts

Posted - 01/29/2017 :  1:51:27 PM  Show Profile  Reply with Quote
Did you ever resolve this problem? I have a R845A and am trying to install the Ecobee3. I have no experience with electrical work and I had an electrician here doing a few other small projects who said it wouldn't be possible. I was hoping there would be some way of wiring this by now.
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stusviews
Moderator

USA
15603 Posts

Posted - 01/29/2017 :  1:58:28 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
quote:
Originally posted by blckout20

Did you ever resolve this problem? I have a R845A and am trying to install the Ecobee3. I have no experience with electrical work and I had an electrician here doing a few other small projects who said it wouldn't be possible. I was hoping there would be some way of wiring this by now.


Provide more details about your HVAC system and how you control it now.

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blckout20
Starting Member

2 Posts

Posted - 05/30/2017 :  09:35:53 AM  Show Profile  Reply with Quote
I have a normal programmable Honeywell thermostat currently with two wires (R and W) running to it. I am trying to install the Ecobee3 to control the heating of the house on the main floor. I have two zones (upstairs and downstairs) but am not currently concerned with the upstairs thermostat. I have baseboard radiators which I believe are heated by a boiler?

The boiler has a Honeywell R845A which the electrician told me does not have a C post, as mentioned by the OP, and therefore could not provide power to the new thermostat. I seem to be in a similar situation as the OP but am not knowledgeable about anything relating to HVAC or electrical work. Honeywell support has said that I can buy a 24vac step down transformer (is this basically the same as what is posted?) that will connect directly to the Rc and C input on the thermostat and provide power? Is this correct?

Edited by - blckout20 on 05/30/2017 09:47:34 AM
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stusviews
Moderator

USA
15603 Posts

Posted - 05/30/2017 :  11:51:39 AM  Show Profile  Visit stusviews's Homepage  Reply with Quote
Yes, that is correct. A 24VAC transformer for an HVAC is easy to find and not costly. The lowest amperage is adequate as is the lowest cost transformer.

BTW, virtually every heating system has a C (common) connection, but sometimes they're not easily seen. But that wouldn't help unless you had at least three wires in the thermostat cable.

Stu's Views is Education and Fun. What do YOU want to VIEW today?
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Edited by - stusviews on 05/30/2017 12:02:30 PM
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