Wiring with separate heat and air, have common feom heat

[TheSizz]

Ok have a new nest to install. I'll provide a quick summary of what I have. Have a separate hot water heat boiler in basement and a separate ac unit in attic. Ok now for the wiring , have a 3 conductor to air handler (Rc,Y,G) and have a 3 conductor to basement boiler(Rh,W, and an unused green) there is a taco multizone controller on boiler so easy as pie to connect the green to common. The air handler is not accessible at this time.(tenant) Can the stat be powered from the Rh and common or does it need to draw power from Rc and common? I need to give the guy a price. I know I can use the green going to AH and lose option of always on fan, which the guy doesn't use FAN ON anyways., but again is problem getting to air handler.  Snaking a new wire to ah is not feasible as stat is on knee wall/divider wall, so it doesn't touch ceiling and is on slab. Will the stat work with getting power from the heat system? Its a 5 minute job that way. Thanks in advance.  

[Houptee]

No you need the Rc and C common from the Air Handler for it to keep battery charged.

The boiler only needs to connect to Rh and W once you get the main power coming in from the air handler.

[Jhonleanmel]

Hey folks, 

Thanks again for helping here, @Houptee. 
@TheSizz, I hope you've got the answer you're looking for. If you're still in need of any assistance, feel free to let us know. 

Best,
Mel

[TheSizz]

Thanks, so it follows the others..lol. we always wired homes with a 3 wire to ac and a 3 wire to boiler, and also for the door bells. This way you only had to keep one coil with you on rough ins, and I know a few others that also did same. So many houses have a spare to the boiler, because of that. Now in past 10 or more years it became common to have a 3 to boiler and 5 to ac( assuming single stage) . I don't understand why they can't design these so can be powered off either, I know some can take a separate 24v which also works well 

[Jhonleanmel]

Hi TheSizz,

I suggest that you contact a pro installer to discuss other possible options. 

Best,

Mel

[TheSizz]

Lol too funny.

[Jhonleanmel]

Hi TheSizz,

I understand that this is not the answer you're looking for, but we value your safety, which is why I suggest reaching out to a Nest Pro Installer so they can safely wire your system and give you other options.

Best,

Mel

[TheSizz]

Lol, I'm a 36 year plus licensed electrician,  I've done multiple trane building management systems, 1000s of multi stage heat/air systems with emergency heat, for cdc(community development centers/government funded energy deduction grants for large apartment complexes) and installed honeywell 3stage heat/air w/emergency heat stats. I've helped do rewiring in the world trade center after the 93 basement bombing. Setup multiple home automation systems, wired many industry building., etc.. So to be concerned about my safety in this is why i laugh. I merely asked if the stat would work with the voltage being supplied thru the rh and common,  as opposed to the rc. Some older stats pre(wifi and other wireless protocols, had the option (two voltage regulators with diodes) or a separate power input.  I've only asked because the tech support for nest is a joke, and they have no idea... because I was unable to access the air handler unit in attic, because of a problem with the tenant. So I winded up getting to unit through its return system..and took my green wire from fan on relay to common grounded side of transformer!!! So all is good. I usually have access to either unit, and in this situation I did not, hence the question if this newer learning stat had simple 20 cents worth of electronics to power itself from either way!! 

[Jhonleanmel]

Hi TheSizz,

Thanks for reaching out and I'm sorry to hear that you're still having an issue with your Google Nest Wifi. We'd like to take a deeper look into this — could you fill out this form and let us know once you're done?

Thanks,
Mel

[Princesss]

Hi TheSizz,
 

Chiming in-- have you had the chance to fill out the form?

Best,

Princess

[TheSizz]

Princess, 

  I looked at the form just now, and it too, suggest that there is still a problem that needs to be addressed!! , so why would I fill that out to waste both their's and my time, for a non-existent problem? If you have additional information on why I should fill out the form, please advise why? Thank you!! 

[Markjosephp]

Hi TheSizz,

We're sorry for the confusion that this caused you, and thanks for clarifying that it's working fine now.

There's no need to fill out the form, but if you have additional questions or concerns, let us know as we will be locking this thread in 24 hours.

Best regards,

Mark

[TheSizz]

There is no problem? Why would you state there is? I asked a question, on which 2 terminals the stat received power from, and that was answered, I asked because we didn't have access to the air handler on 2nd floor/convered to a apartment.  I was able to get to the unit by unscrewing the return box and pushing it up. I then rewired the unit to get my grounded/common 24v. All worked fine. Why do you insist there is a problem?