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Old 03-14-2020, 07:53 PM   #1
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My thermostat with separate O and B terminals


Hey guys, I think I have the same issue. I bought an ecobee4 and they say that because I have a B and an O, that I can't use it?
I have an AC unit sitting outside and a natural gas furnace in my basement.
Can I make this work somehow?
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Old 03-14-2020, 10:33 PM   #2
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Re: My thermostat with separate O and B terminals


Post pics of how the furnace and A/C are wired.
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Old 03-14-2020, 10:39 PM   #3
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Re: My thermostat with separate O and B terminals


Do you have a zoning system?

Old ones used O/B terminals for change-over.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.
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Old 03-15-2020, 12:55 AM   #4
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Re: My thermostat with separate O and B terminals


As asked, do you have a zoning system? And do you have a heat pump/hybrid system?
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Old 03-15-2020, 01:31 PM   #5
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This is what my current thermostat setup looks like.
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Old 03-15-2020, 01:38 PM   #6
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My furnace and AC unit are separate. I don't know what a heat pump even is, but due to having two units, I'm guessing the heater can't also cool...
Its a Rheem, here is the panel on it.
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Old 03-15-2020, 01:40 PM   #7
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I don't think I have zoning... this one thermostat makes all vents blow, I can't make the upstairs blow only - if thats what zoning means.
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Old 03-15-2020, 01:46 PM   #8
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Re: My thermostat with separate O and B terminals


You have a fossil fuel kit - likely heats with heatpump and when the outdoor temperature drops below a certain point, switches to gas.

You have a blue wire connected to B on the stat but i don't see that wire on the fossil fuel kit.

Can you see where that wire goes on the other end?

Can you give the model number of the existing thermostat and base?

The ecobee is capable of controlling dual fuel on it's own but it would be simpler for you to set it up for a straight heatpump and let the fossil fuel kit do the change-over.

It's better to use an advanced stat to do the change-over as it has more options but it's not really something for the novice to deal with.

If the furnace is natural gas, at today's prices it may make sense not to use the heatpump. Would need to know the outdoor unit model number and your utility rates for fuel and electricity.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 03-15-2020 at 01:58 PM.
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Old 03-15-2020, 01:54 PM   #9
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Re: My thermostat with separate O and B terminals


Here's an information page on heatpumps: https://www.nrcan.gc.ca/energy/publi...heat-pump/6831
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Old 03-15-2020, 01:55 PM   #10
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Current thermostat is a T725 Pro1 brand.
I think my furnace is gas primarily, not just when its super cold? I live in southern Missouri, we have very mild winters and my gas bill would be smaller if it didn't use it much - I don't cook with gas. The fluctuation is large from say Januarys bill vs July.
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Old 03-15-2020, 02:00 PM   #11
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Re: My thermostat with separate O and B terminals


Your setup I believe uses an outdoor thermostat to do the change-over.

It may be set high so that the furnace does most if not all the heating.


The existing stat is heatpump only.

Can you see what that blue/B wire connects to on the other end? it may just be capped off, in which case you can leave it disconnected when changing the stat.
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I am not in the business of any trade I give advice on. I have non-professional hvac experience + good knowledge of theory. Attempt repairs at your own risk. Never jump out safeties - especially pressure switches - on a furnace for testing with fuel supply on; use a meter. Do not troubleshoot with live line voltage present unless there's no alternative.

Last edited by user_12345a; 03-15-2020 at 02:04 PM.
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Old 03-15-2020, 02:01 PM   #12
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Outside AC unit
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Old 03-15-2020, 02:01 PM   #13
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Natural Gas
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Old 03-15-2020, 02:02 PM   #14
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The blue wire goes to the outside unit.
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Old 03-15-2020, 02:08 PM   #15
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This is the ecobee4 base. What do I put where?
And why did my old one have a jumper, a wire from E to W2? Should I do that to the ecobee too?
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