I am pulling the permit and installing the electrical wiring for my Waterfurnace 7 Series 4-ton Ground Source Heat Pump / Furnace. These are the components:

My questions:

  • Is it fair to say I need two separate circuits for this equipment? That seems clear to me, but I feel I should ask.
  • 6/2 wiring should suffice for both of these circuits in terms of amperage for the equipment in question, correct? The maximum amperage as I understand for 6 gauge wire is 55A. Per the documentation and screenshots below, the aux heater should draw a maximum of 40A at 240 V; and the furnace is requiring a 50A breaker, meaning the breaker will trip before it reaches the maximum of 55A for the wire gauge.

The unit is being installed in an unfinished basement, replacing a propane furnace. I will be running all wiring from the panel, to the unit. Wiring will be 6/2 romex from the top of the load center / breaker box, traveling along the sill and along the joists, stapled every 12"-16". While not fully required (because the panel is within direct eyesight of the furnace), but best practice, I am installing 60A physical disconnects on a plywood panel at eye level for each circuit. Where the wiring departs the joists and travels to the disconnects, I am using flexible non-metal 'liquid proof' conduit for ease of install over PVC or metal conduit.

My circuit plans are as followed:

  • A 50A breaker with 6/2 romex for the furnace
  • A 60A breaker with 6/2 romex for the auxiliary heater

Technical Details of Equipment:

Furnace: Furnace Electrical Ratings

Furnace Wiring Diagram: enter image description here

Auxiliary Heater: Auxiliary Heater Electrical Ratings

Auxiliary Heater Wiring Diagram:

Heater diagram

Please let me know if you have any questions or clarifications. I appreciate any tips, advice, critiques, or feedback. I'll be happy to answer any questions I haven't addressed. Thank you!

  • 1
    A) Well asked! B) A phone screenshot is better than nothing, but a link to the Aux Heater installation instructions would be even better than that. C) Sch 40 conduit (the grey stuff, not white plumbing pipe) is pretty simple to install, much cheaper than Liquid Tight, and much, much easier to pull wire through.
    – FreeMan
    Feb 16, 2023 at 13:06
  • @FreeMan. Thanks! B) Added! C) Yeah, I kinda thought that. Regardless, I've already got the liquid tight :). Any thoughts on the primary questions around the wiring + circuit sizes? Thank you! I haven't been able to find an online copy of the install manual for the aux heater, btw.
    – Davek804
    Feb 16, 2023 at 14:32
  • Sorry, that's about all the help I'm able to provide at the moment. One of the electricians will be along shortly, I'm sure. A pic without the glare of the plastic sleeve would be a bit easier to read, though. ;)
    – FreeMan
    Feb 16, 2023 at 15:52
  • 2
    Why in heck would you have aux heat for a ground source heat pump?
    – Ecnerwal
    Oct 16, 2023 at 16:14
  • The aux heat supplements the heat pump when demand exceeds supply. It's cheaper to cover peak demand with resistive heating than to upsize the geo to handle it.
    – MadMonty
    Mar 26 at 21:19

1 Answer 1


The ampacity of a given cable depends on several factors (e.g. conductor, insulation, ambient temp, number of conductors within confined space), which are incompletely specified. However, you stipulate that your #6 is rated for 50A, a reasonable assumption. The breaker protecting that wiring should be rated the same or lower, thus <=50A, not 60A as you intend.
I didn't see your location, but for USA, I look to NEC 2023, Section 310.21, Table 310.16, Ampacities of Insulated Conductors with not more than three current-carrying conductors in Raceway, Cable, or Earth.

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