proper breaker and wire size for gas furnace

Discussion in 'HVAC Heating & Cooling' started by estone, Apr 14, 2013.

  1. estone

    estone New Member

    Messages:
    72
    Location:
    Colorado
    I had a Heil gas furnace installed that will be primarily used for a/c but it does have a heat too, Model N8MSN0701716A1. I installed the electrical with a 20 amp breaker/ 12-2 wire as per HVAC installer instructions. After searching online electrical data it calls for a 15amp breaker/14-2 wire, max. unit amps 9.5. It also says max. wire length 29ft. I have the furnace installed in my attic so I'm running close to 40 ft. of wire from the basement panel to attic. I'm really sweating this and was hoping I'm ok with the 20amp breaker/ 12-2 wire. If what I went with is really a no no I guess I can rip it out and start from scratch but I was hoping I would be ok. I would appreciate your expertise. Thanks in advance!
  2. DonL

    DonL Jack of all trades

    Messages:
    3,812
    Location:
    Houston, TX

    The Wire is fine, And the breaker is fine also.

    Do not sweat it, You can install a 15 amp breaker if it would make you feel better.
    Last edited: Apr 14, 2013
  3. estone

    estone New Member

    Messages:
    72
    Location:
    Colorado
    Installing the 15amp breaker with the 12-2 is ok? I thought a 15amp breaker had to be 14-2 wire, 20amp/12-2, 30amp/10-2? Or is that just good practice?
  4. DonL

    DonL Jack of all trades

    Messages:
    3,812
    Location:
    Houston, TX

    The wire is larger and can carry more current / power then needed for your unit, and is better than 14 gauge.

    A 15 amp breaker would trip quicker if your unit had a fault.

    The breaker is to protect the wire from over heating, and your wire is better than needed for 15 amps.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    12g is the MINIMUM wire size for a 20A CB, but 12g, because it IS bigger, will have less resistance when supplying a lower current. So, based on the max length for 14g wire in the installation manual, the use of 12g is called for, and is a GOOD thing. I'd use the recommended CB size of 15A with it. CB is designed to primarily protect the wiring, not the device, so ANY CB 20A or less is good. Using a 15A is closer to the device's rating, and would also help protect the device in addition to the wiring.
  6. estone

    estone New Member

    Messages:
    72
    Location:
    Colorado
    Thanks for all the help. I will sleep better now.
Similar Threads: proper breaker
Forum Title Date
HVAC Heating & Cooling Carrier Infinity system - shows incorrect temp and not cooling properly Aug 6, 2011
HVAC Heating & Cooling need help with proper AC size Jul 24, 2009
HVAC Heating & Cooling Proper Crawl Space Ventilation Apr 18, 2008
HVAC Heating & Cooling Proper Aquastat Settings Nov 8, 2007
HVAC Heating & Cooling Improper Install Feb 26, 2007

Share This Page