Adding a relay for summer fan control?


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Old 12-28-17, 07:14 PM
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Adding a relay for summer fan control?

Hello,

I'm in the process of spending a lot on my furnace and wanted to figure the costs for adding thermostat control of fan only for summer usage.

I currently have a 5-wire cable going to my thermostat. Currently, only two wires are in use for the burner. (no common)

I'd Ideally like to add a 24Vac in for common as well as splice in a relay for the fan override switch. Would this be possible with the 5 wire cable or would I need to pick one or the other?

As for the fan relay, would the low voltage side work with a thermostat out of box, or would I need to have a specific voltage load made available?
Worst Case scenario I could likely get lazy and wire in a Z-Wave compatible toggle switch.
 
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Old 12-28-17, 07:18 PM
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You'd need four wires.....
R - 24vac
W - heat
C - common
G - fan

You may be able to just add a relay at the furnace for the blower. Any thermostat would work. I'd need a make and model for more detail.
 
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Old 12-28-17, 07:55 PM
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Currently I have an old oil burner furnace with a Honeywell Stack Limit switch. I assume R and W would be connected to that?
The blower Fan's override is currently just a 120VAC toggle switch on the back side of the furnace.

I'm looking at this thermostat https://www.amazon.com/Z-wave-Thermo...ave+thermostat
 
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Old 12-28-17, 08:11 PM
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I'd need a model number for the stack switch. It may not be able to power a wifi stat.
Ideally in a situation like you have you'd use what's called a fan center. It's a combination transformer and relay in one. It would power the thermostat and the relay would run the blower.

This is one example.... there are many to choose from. They all do basically the same thing.
Honeywell-R8285A1048-Center-Fan-Control/dp/B009PAOLPG

With amazon.... if you look at one item... like this.... and then the stat..... it will combine the two in a package price.
 
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Old 12-29-17, 12:13 PM
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Thanks PJ!

MY stack control is a RA116A1055
https://customer.honeywell.com/en-US...d=RA116A1055/U

Photo
imgbox - fast, simple image host

I have 5 wires on my thermostat cable.

Red (Stack Control W(T)
Yellow (Unused)
White (Unused)
Green (Unused)
Blue (Stack Control B(T)


here's what the switches on my furnace look like.
imgbox - fast, simple image host

The fan Override is on the upper right.
 
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Old 12-29-17, 12:53 PM
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k,
Due to the age of your furnace you have a fan/limit switch that controls the blower and high limit on the furnace.

It may be a Honeywell with a white button on it. If it is that white button when pushed in is for constant fan operation in the summer, overriding the burner circuit so the furnace doesn't fire. Just the blower runs and you can control it with your service switch upstairs.

Do you have a pic of your fan/limit switch. If it doesn't have the button you can get a control with the button.

That's the simplest way with what you have.

http://www.supplyhouse.com/

If you go here and type in L4064B2236 in the search bar you can see the part.

Hope this helps a little.
 
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Old 12-29-17, 01:38 PM
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There is a red button on the face of my fan control box.

The Limit switch is in this photo Marked Limit., The Fan override is the standalone box to the right of it (well above in the rotated photo)
imgbox - fast, simple image host
 
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Old 12-29-17, 02:31 PM
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Those are just toggle switches connected to your actual fan/ limit control.

I would need to see a pic of the control. If the flame switch was turned off which is most likely tied into your stack relay and the other 2 turned on could you control the fan from your service switch upstairs.
 
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Old 12-29-17, 06:13 PM
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He didn't just want to control the blower.... he wanted to add a wifi thermostat too.

That is only a two wire stack control. It won't support a wifi stat. You may be able to use a power stealing stat like the nest but there are no guarantees it will work and it can't control the blower separately.

If you want both..... you'll need a fan center.
 
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Old 12-29-17, 08:59 PM
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A fan center sounds about right, I would add that to where the override/summer fan switch is correct?

Here's my fan controller (the thing belongs in a museum)
https://imgur.com/a/DACFf
https://imgur.com/a/T82RI
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Last edited by PJmax; 12-29-17 at 09:14 PM. Reason: added pic from link
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Old 12-29-17, 09:16 PM
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That controller serves two functions. One is a high heat limit and the other is blower control. That unit needs to stay in place and the fan center relay will connect to the same two wires that run the blower.
 
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Old 12-29-17, 09:45 PM
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I thought he just wanted a quick way to run the blower in the summer.
 
 

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