Trying to wire for washer/dryer combo in the garage, and we need to add a tankless water heater to get hot water to the washer. In their current location, there's a (EDIT: 15) AMP circuit for washer, and one for the dryer. Both are electric. The water heater requires up to 33A, and needs a double-pole 40A breaker. It also runs 240V (washer 110, dryer 240). To make this fit in the box, I'm hoping I can make some combo of either the washer or dryer on that double pole as well.

EDIT TO CLARIFY: We have two open spaces to work with in the panel, I'm trying to see how I can combine one of the other appliances with the heater in that open 2-pole spot. (See @Harper below)

Electrical newbie, but am I correct in thinking that the best way would be: -50A double pole with 6/3 to the heater (max 33A) and washer (Dr. Google says max 10). I already ran 10/3, but it looks like that's nowhere near enough to carry this load. It's exposed 20 feet, so I don't mind re-running. -Leave the dryer on dedicated 30A circuit.

Does this sound reasonable? Is there a simpler way that I am missing? (or is this DOA and all three need to be on different circuits?)

Thanks! Jeff

  • Your washer is on a 30 A circuit? That's rather atypical - are you sure it's not a regular 15 or 20 A?
    – mmathis
    Apr 29, 2017 at 19:36
  • to make this fit in the box. You're saying you only have 2 spaces left in your service panel and that will only fit one 2-pole breaker. Ok. That's solvable, but not that way. Apr 29, 2017 at 20:11
  • Is the garage attached or detached? Apr 29, 2017 at 20:13
  • @mmathis- you're right. Washer is only on 15. Apologies.
    – T-House
    Apr 30, 2017 at 0:06
  • 1
    @user50459 15 and 20 A circuits can supply many fixtures, but anything higher must be on a dedicated circuit. So, your dryer and heater need to be separate. Your panel may accommodate tandem breakers, which put 2 (120 V, generally 15 or 20 A) circuits into 1 space in the panel. If your panel supports these, that could free up space for another 240 V breaker.
    – mmathis
    Apr 30, 2017 at 3:13

1 Answer 1


I think what you mean to say is you need a quadruplex 40/30.

The tankless would be fed with a #8/2 #6/2 to suffice the 33 amp requirement. ( black/white/ground ) unless for some reason it requires a neutral then #8/3 #6/3 ( Black/red/white/ground ).

The existing dryer 30 amp breaker would be replaced with the quadruplex. The dryer #10 would connect to the 30 amp side, and the #6 would connect to the 40 amp side.

Note: The panel should indicate how many, if any, quadruplex it can allocate. Also, the breaker obviously needs to match the panels manufacturer.

  • There is already a 30-A 2-pole 240 V breaker for the dryer, right? Why not just add a 40-A 2-pole breaker for the tankless water heater? Why use the "quadruplex" 40/30? Apr 30, 2017 at 3:03
  • 1
    I got my quadruplexs & tandems mixed up. I thought his panel was full..no?
    – Kris
    Apr 30, 2017 at 4:00

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