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Discussion Starter · #1 ·
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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Post pics of how the furnace and A/C are wired.
 

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Do you have a zoning system?

Old ones used O/B terminals for change-over.
 

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Discussion Starter · #7 ·
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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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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Discussion Starter · #10 ·
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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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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That's a heatpump.

B is energized in heating mode and O is energized in cooling mode - it signals the heatpump which mode.

Rheem uses B instead of O for the change-over but that fossil fuel kit is expecting O for input.

Since new stats can not use both, wiring modification will be required.

I don't know if the fossil fuel kit absolutely needs the O input but it's better to be safe.

Either a (normally closed_ relay will have to be added to apply power to O when B isn't energized or you'll have to bypass the fossil fuel kit and use the stat to control duel fuel.

I favour the latter.

The setup is a bit complicated -> have to go through the settings menu of the new stat.
 

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Do you see an outdoor thermostat anywhere?

Follow the wire from fossil fuel kit.

Is your furnace propane or natural gas?

What are your utility rates? (add up all delivery charges per kwh and cubic ft of gas)

And why did my old one have a jumper, a wire from E to W2? Should I do that to the ecobee too?
Emergency heat mode automatically bypasses the heatpump and energizes E instead.

In most cases, emergency heat isn't a separate system -> so they get jumpered.

The ecobee doesn't come with an E terminal so there would be no jumper.
 

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Which version of the ecobee do you have?

I'll have to look up the setup manual to give step by step instructions.

Best thing to do is take the fossil fuel kit out of the circuit and use the ecobee for everything.

It's a great stat for dual fuel.
 
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