new HVAC wiring

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Old 10-04-18, 08:24 AM
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new HVAC wiring

I am having an HVAC upgrade done soon. My current electric forced air furnace is circa 1979. I am having a heat pump/air handler unit installed next month, and I am trying to save money by performing my own electrical work to install a service disconnect to the outside heat pump unit. It will be just on the outside wall adjacent to the existing furnace in the garage. The heat pump will require 40 amp service, so I had planned on running some 6/3 romex from the main breaker panel to the new service disconnect. the main panel is on the opposite wall of the garage (of course), and the walls are finished so this would require a 40 foot run of conduit to the location of the outside heat pump disconnect panel.
The existing furnace has two separate 60 amp circuits servicing what I am assuming are the fan and the heating elements. There are also two 60 amp breakers on the furnace panel functioning as the service disconnects. I think the new air handler unit will likely only take 40 amp service.
I was wondering if I could just "re-route" one of the 60 amp disconnects to make a short run (probably 6-8 feet max) for the outside disconnect panel for the heat pump (it's a single stage unit which only needs a 40 amp service). disclaimer: I'm a relative novice to electrical DIY, so I apologize if my terminology is incorrect. I've done my share of rewiring for outlets, lighting, and even a clothes dryer but nothing like this.
any input and guidance would be appreciated!
thanks,
Brandon
 
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Old 10-04-18, 10:18 AM
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If the wiring is in good condition and it includes a bare ground wire in the cable, yes you could re-use one of the existing 240V 60A circuits for the new heat pump unit as long as you replace the double pole 60A breaker with a double pole 40A breaker.
 
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Old 10-04-18, 11:57 AM
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Also, if you do decide to run new 6/3 (or possibly 6/2 depending on the furnace requirements), you may or may not need to put it in conduit. You really only need to use conduit if/where the cable is "subject to damage". So if you're running it along the corner of the ceiling, it's probably not subject to damage and likely doesn't need to be in conduit.
 
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Old 10-04-18, 04:28 PM
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that's great news, thanks!
 
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Old 10-04-18, 05:03 PM
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The heat pump will require 40 amp service,
I think you may have misread the tag.
That would be an extremely large condenser..... probably in the 5+ ton area.
 
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Old 10-09-18, 11:37 AM
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I think the new air handler unit will likely only take 40 amp service.

What are you using for emergency heat when outside temperatures drop low enough that the heat pump will no longer heat the house? I am not familiar with the winter climate conditions in your area, but the simple fact that you had a 20 KW electric furnace before tells me you'll also need 20 KW emergency heat and a 40 amp circuit won't cut it.
 
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Old 10-09-18, 02:49 PM
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Hi, what are the nameplate specís on that condenser, usually it states wire size and max OC protection.
Geo
 
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Old 10-09-18, 07:04 PM
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The OP had two 60A circuits to an electric furnace. Now only one will be used for the supplemental electric heat of the heat pump. The supplemental heat is not usually large enough to heat the house to the same comfort level as when the heat pump is running.

I will agree though that a 40A to the air handler may be on the small side and will only run approx 8Kw of supplemental heating.
 
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