My water heater went out and I'd like to replace it with a tankless. Electrical setup is as follows:

A.O.Smith 50gal water heater - 1, 30amp double pole breaker

Tankless needs - 2, 40amp double pole breakers

I have a 125amp Eaton breaker box. I'd like to know if I can replace the 30amp DP with a 40amp DP, add another 40amp DP, run 8 gauge wire, and still keep the same 125amp breaker box without doing damage or running the possibility of burning the condo down?

Thanks in advance for any help.


  • 1
    How many square feet is the condo, what size is the feeder into your panel, how many kitchen branch circuits are present, and if you have electric heating appliances (dryer, range, HVAC), what are their nameplate ratings? – ThreePhaseEel Oct 13 '16 at 0:12
  • The condo is just under 1000 sqft. I'm not sure the size of the feeder line coming into the panel, I believe it's 2, 4 gauge wires. HVAC - Min Ampacity 47.5/52.5 Max Overcure Protection 50/60 Dryer - Can't find exact info, but it's on a 30amp DP Range - Can't find exact info, but it's on a 40amp DP Kitchen Circuits: Microwave - 20amp Disposal/Dishwasher - 15amp DP GFI - 20amp (x2) Not sure if those specs help but I'll work on getting more info. – RyanSweet Oct 13 '16 at 0:48
  • 1000sqf and a 50 amp MOP on the AC? That doesn't sound right. Where do you live... Hades? Anyway ;) are you sure it needs two 2-pole 40a breakers? If it does, do you really think you need that much recovery? Are you running a laundromat? ;p – Mazura Oct 13 '16 at 1:36
  • Good ol Indiana. I save a lot during the summer months. Lol. I was looking at the Ecosmart Eco 18. It has 2 elements and each requires a 40amp DP with a ground for each. According to the Ecosmart website, that unit in this area will run 2 low flow showers. – RyanSweet Oct 13 '16 at 1:54
  • I'd go at least 1 model up from that unless you're really only going to use 1 shower at a time. Their map is based on 105 degree outlet temp. Nobody sets their water heater at 105. Come winter time here I bet you're not going to be very happy. – topshot Oct 13 '16 at 2:17

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