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Calculators / Water and power

Can your deck and panel handle a hot tub?

Grab the tub's spec sheet. We'll work out what it weighs full, what that does to a deck, and if your panel has room for the circuit.

These are example numbers. Put in yours.

The tub

lb

Empty weight, from the spec sheet.

gal

Most 6-seat tubs hold 350 to 450 gallons.

people
in

Outside of the cabinet.

in

Where it goes and how it plugs in

Where it sits
Power

The spec sheet lists it. Bigger tubs are 240 V.

Your panel

Main breaker

The big breaker at the top of the panel. The number is on the handle.

sq ft

Finished, lived-in floor space.

Water heater
Clothes dryer
Heat and AC
EV charger
kW

Pool pump, well pump, sauna, shop heater. Add up the nameplates. Leave blank if none.

Range or oven

Your deck can't hold it

108 psf on a 50 psf deck

Filled with 6 people in it, the tub weighs 5,296 lb. That's about 2.2 times what a normal deck is built for.

Full weight
5,296 lb
Load
108 psfdeck built for 50
Panel
86 Aof 100 A
Tub circuit
240 V, 50 A

water = 400 gal × 8.34 lb = 3,336 lb

people = 6 × 185 lb = 1,110 lb

full = 850 + 3,336 + 1,110 = 5,296 lb

footprint = 84 in × 84 in ÷ 144 = 49 sq ft

load = 5,296 lb ÷ 49 sq ft = 108 psf vs 50 psf deck

tub = 240 V × 50 A × 80% = 9.6 kVA

lights and plugs = 1800 sq ft × 3 VA = 5.4 kVA

house loads = 5.4 kVA + kitchen and laundry circuits 4.5 kVA + appliances 7.5 kVA + hot tub 9.6 kVA = 27 kVA

counted = 8 kVA + (27 kVA − 8 kVA) × 40% = 15.6 kVA

with heat and AC at 100% = 15.6 kVA + 5 kVA = 20.6 kVA

load = 20.6 kVA ÷ 240 V = 86 A of your 100 A panel

The two checks

  • Weight5,296 lb full over 49 sq ft
    108 psf on a 50 psf deck

    Too heavy for a deck built to normal code. Pour a pad or get an engineer.

  • Panel86 A of 100 A with the tub
    14 A to spare

    Room for a 240 V, 50 A tub circuit.

Do this

Put it on a 4 to 6 in concrete pad at ground level, or pay an engineer to beef up the deck. Extra joists alone won't fix the posts and footings.

GFCI and disconnect

The 50 A circuit needs GFCI protection (NEC 680.44). The shutoff goes within sight of the tub and at least 5 ft from the water (NEC 680.13). Most people use a spa panel with a GFCI breaker.

Permit

A 240 V tub circuit takes an electrical permit in most towns. Many inspectors also check the pad or deck.

How we work it out

First the weight. Water is heavy, and so are the people in it.

full weight = dry weight + gallons × 8.34 lb + seats × 185 lb

load = full weight ÷ footprint in sq ft

A deck built to code is designed for 50 psf: 40 for people and 10 for the deck. Most full tubs land between 100 and 130 psf. That's why we say put it on a concrete pad, or have an engineer design the deck for it.

Then the power. We add the tub to your house with the NEC 220.83 method for existing homes. In the 2026 NEC that section moved to 120.83. Lights and plugs count 3 VA per sq ft. Appliances count at nameplate. The first 8 kVA counts in full, the rest at 40%, and heat and AC count in full on top.

tub load = volts × breaker amps × 80%

panel amps = total VA ÷ 240 V

If that comes out over your main breaker, the tub won't fit without changes. Under 10 A to spare, we call it tight. A 240 V tub also needs GFCI protection and a shutoff within sight of the tub, at least 5 ft from the water.

Where the numbers come from

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