I need to find out... is there any reason I cannot power the majority of my house on one generator (including furnace/blower), and the whole house A/C condenser on another?

I'm pretty sure the answer is "no issues" but the concern I'm seeing is the signal cable between the furnace and condenser, that activates the condenser.  Is that connection of the AC or DC variety?

If you're looking for a reason, it's efficiency; I don't need a 10k or 12k generator to run my whole house, but I do need a 7KW to kick off the condenser.  I want to run a modest generator to power the rest of the house, and a dedicated generator to just feed power to the condenser when demanded.  Both units would be fed natural gas for fuel.

Thanks!

Not an electrician but have had enough shorts and Zaps to learn a thing or 2.

DO NOT DO IT!     If you are trying to run this using house wiring,  unless the 2 generators are in the proper phasing, (Available in electronically controlled output  gensets, Search "paralleling inverter generator") very bad things will happen.  Generator explosion, burning house wiring.  Essentially what you could have is the same as touching 2 legs of 220 circuit together.

You need to consider the neutral wiring as well as the "hot" legs.

If you are talking about plugging cords to individual appliances that should be no problem as long as the 2 gens are electrically isolated.  Ie AC gets plugged in Gen1  and Fridge gets plugged into Gen2.

 

How often is your power out when you really need AC? Thats alot of extra money just to run your condenser between the generator plus proper wiring and gas pipe. Id just run a fan at the foot of my bed and buy a new gun. But then again I grew up without AC 

1 hour ago, Sota said:

I need to find out... is there any reason I cannot power the majority of my house on one generator (including furnace/blower), and the whole house A/C condenser on another?

I'm pretty sure the answer is "no issues" but the concern I'm seeing is the signal cable between the furnace and condenser, that activates the condenser.  Is that connection of the AC or DC variety?

If you're looking for a reason, it's efficiency; I don't need a 10k or 12k generator to run my whole house, but I do need a 7KW to kick off the condenser.  I want to run a modest generator to power the rest of the house, and a dedicated generator to just feed power to the condenser when demanded.  Both units would be fed natural gas for fuel.

Thanks!

In most HVAC, the "system" is controlled through the furnace.   The AC just has two low voltage wires, C/Y that close when AC is called.  This closes a coil that pulls down a contactor which then kicks the condenser on.  The furnace then handles the air handler, speeds and whatnot.

The problem is every system is a bit different, specially if you have a multi-stage heat pump.    In theory you could drive the high amperage AC to the condenser from one Genset and get the low voltage control circuitry from the furnace transformer which is running on a different genset.  I see no real reason why this wouldn't work.  The problem is your system could be different.

A better solution would be to have your Furnace and AC unit on one genset, 100% isolated.  This means you need to put a pigtail on both units that you unplug and transfer to a different outlet so you are not co-mingling neutrals or grounds.  The low voltage side grounds through the transformer and the transformer grounds to AC.  If your condenser is just a two wire coil and no case ground, it would be fine as it would be isolated.  If the low voltage side has a 3rd wire case ground to the condenser, you have a path from one genset to the other through that ground and that's bad mojo.

  Your gas furnace is probably 110v.  They hardly use any electricity.  This means it's using one leg hot, one neutral at 110v.  Your AC is 220v using two hots, probably a ground, , maybe a neutral, probably not.  Maybe all 4, probably not.  It all depends on what it is.

 

 

 

 

 

@PeteF The phasing isn't a problem, as the units wouldn't have tied together legs; the condenser would be mechanically disconnected from its main electrical source (panel) and mechanically connected to the generator.

@Malsua the condenser only has 2 hots and a ground, no neutral.
I've considered electrically isolating the air handler on the same generator as the condenser, the problem is as you noted, the air handler doesn't use a lot of power, and if I needed it in the winter it'd be bound to a big generator that'd be wasting a lot of power.  Or i'd have to have a much more complicated switching system for it.
My setup is indeed an older 4 wire control system, so no fancy multi-stage shit here.

@fishnut it's not unheard of, plus we just had it happen today as well, where power was out for several hours during the hottest part of the day. My "backup" plan has been to if needed, drag out of the shed a couple (2 or 3) spare window A/C units if there was a long term outage.  I'd like to try and do better.

Most of this stems from the fact I  need to get off my ass and get the automated genset activation working, so I don't have another service outage.

 

 

2 minutes ago, Sota said:

@PeteF The phasing isn't a problem, as the units wouldn't have tied together legs; the condenser would be mechanically disconnected from its main electrical source (panel) and mechanically connected to the generator.

@Malsua the condenser only has 2 hots and a ground, no neutral.
I've considered electrically isolating the air handler on the same generator as the condenser, the problem is as you noted, the air handler doesn't use a lot of power, and if I needed it in the winter it'd be bound to a big generator that'd be wasting a lot of power.  Or i'd have to have a much more complicated switching system for it.
My setup is indeed an older 4 wire control system, so no fancy multi-stage shit here.

@fishnut it's not unheard of, plus we just had it happen today as well, where power was out for several hours during the hottest part of the day. My "backup" plan has been to if needed, drag out of the shed a couple (2 or 3) spare window A/C units if there was a long term outage.  I'd like to try and do better.

Most of this stems from the fact I  need to get off my ass and get the automated genset activation working, so I don't have another service outage.

 

 

I would just verify that you have no continuity via case ground from the condenser to the furnace.  Sometimes they ground via the armored BX.  You need them both 100% isolated  including the ground.  Since grounds and neutral are bonded on your main panel, that means it would be possible for a neutral to send voltage from the hot on one genset, through the neutral to the panel, to the ground, through the furnace to the case ground to the condensor back to the other genset.  Breakers would trip but probably not before the bigger genset would molest the smaller one.  Exceedingly remote possibility and it would require something malfunctioning, but you need to make sure they are not joined in any fashion.

 

 

 

 

Not to mention what about the floating vs bonded neutrals on the gens, beyond my pay grade lol.

2 hours ago, fishnut said:

How often is your power out when you really need AC? Thats alot of extra money just to run your condenser between the generator plus proper wiring and gas pipe. Id just run a fan at the foot of my bed and buy a new gun. But then again I grew up without AC 

This, or just buy a cheap window unit or two.

2 hours ago, SW9racer said:

This, or just buy a cheap window unit or two.

I cooled my last house (1100 sq ft) with a 12,000 BTU Frigidaire (meant for 550 sq ft) and a series of fans. 

15 hours ago, fishnut said:

Id just run a fan at the foot of my bed and buy a new gun.

Leave the gun, take the cannoli.

Mi inlaws have the fixed Generac unit wired in for auto-kickoff.  I can ask them what was involved, but why not just call Gererac and ask them?  I assume they know what they are doing.

I had a 3k that I used to power my house, less A/C, for 13 days during Sandy. I have since upgraded to a 7.5kW unit.

I don't see the economy of buying and ultimately maintaining two pieces of equipment (generators) not to mention the added costs, wiring, transfer switches, and whatever Mother NEC requires with regard to dual (non utility) power sources and the safety ramifications of such as being ultimately economical.