The biggest practical choice after the type of tub is how it gets power. A plug-and-play spa uses a regular outlet; a hardwired spa needs a dedicated 240V circuit. That one difference changes your install cost, your wait for hot water, and how well the tub copes with winter.
This article compares the two. For the rest of the hot tub decisions, start with the hot tub buying guide.
Short answer: plug-and-play saves the electrician but heats slowly. Hardwired costs more up front but heats about four times faster on the same spa. In a cold climate or with daily use, that speed matters.
Side by side
| Plug-and-play (120V) | Hardwired (240V) | |
|---|---|---|
| Example heater | AquaRest Premium 300: 1kW | Same spa converted: 4kW |
| Outlet | Standard 120V/15A | Dedicated 240V/30–40A circuit |
| Install | Plug in (GFCI-protected) | Electrician |
| Heat-up 60°F→102°F, 160 gal | about 16 hours | about 4 hours |
| Cold climates | Can struggle to keep up | Better suited |
Heater figures from AquaRest’s listing. Heat-up times are minimums before heat loss.
The worked example
The EIA defines one Btu as the heat to warm one pound of water by 1°F, and one kWh as 3,412 Btu. The Premium 300 holds 160 gallons, about 1,334 lbs of water (8.34 lbs per gallon, USGS).
Warming it 42°F, from 60°F to 102°F, takes about 56,000 Btu, or 16.4kWh. At 1kW, that’s about 16 hours. At 4kW, about 4 hours.
Here’s what the spec sheet won’t tell you: the energy cost of that heat-up is the same either way, about $3 at 18.34¢/kWh. You’re paying for speed, not efficiency.
Run the numbers on recovery
Heating from cold happens after a refill. Recovery happens every time you use the spa. A 1kW heater puts 3,412 Btu an hour into the water. A 4kW heater puts in four times that.
| Spa | Water | Rise per hour at 1kW | Rise per hour at 4kW |
|---|---|---|---|
| AquaRest Premium 300 | 160 gal | about 2.6°F | about 10°F |
| AquaRest Premium 600 | 240 gal | about 1.7°F | about 7°F |
Our arithmetic, before heat loss.
As an illustration, say the water falls 4°F during a soak with the cover off. On the 160-gallon spa that takes about an hour and a half to recover at 1kW and about 25 minutes at 4kW. On the 240-gallon spa it is over 2 hours against about 35 minutes.
Why a wall outlet limits the heater
A 120V/15A outlet can supply 1,800W in total. The pump, controls, and lights need a share, which is why plug-in spas ship with heaters of about 1kW. A 240V/30–40A circuit has several times that capacity. The limit is the outlet, not the spa.
Spas that can’t be upgraded
Not every plug-in spa converts. In our catalog the LifeSmart LS100DX is 110V only, and the AquaRest Discover Standard 400 is 120V only. With those, the heating speed on day one is the speed you keep. If you might want 240V later, check for the word “convertible” before you buy.
The size rule
The bigger the spa, the more a 1kW heater struggles.
- 160 gallons: about 16 hours from 60°F to 102°F
- 240 gallons: about 25 hours
- 360 gallons: about 37 hours
For a spa over 200 gallons, I’d plan the 240V circuit from the start.
Either way, protect the outlet
A plug-in spa should be on a GFCI-protected outlet, with no extension cord. A hardwired spa gets its protection and disconnect from the electrician. Ask where the disconnect will go, since it has to be reachable.
What each one suits
Plug-and-play: mild climates, a few soaks a week, and anyone who wants to avoid an electrician. You get easy setup. You give up fast recovery after a long soak or a cold night.
Hardwired: cold climates, daily use, or larger spas. You get faster heating. You give up the cost and wait of an electrician and permit.
My rule of thumb: if you have a choice, buy a convertible spa (like the AquaRest Premium 300 or Hot Spring Azure), start on 120V, and upgrade if the heat-up bothers you.
To compare a plug-and-play spa, a convertible spa, and an inflatable, see our hot tub comparison.
Bottom line: 120V buys convenience, 240V buys time. Decide which one you’ll miss more.
Sources
- AquaRest Discover Premium 300 listing (1kW/4kW convertible heater, 160 gallons, 120V/15A and 240V/30–40A), checked September 2026
- U.S. Energy Information Administration, “British thermal units (Btu),” accessed October 5, 2026: eia.gov
- U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A (residential average 18.34¢/kWh, June 2026 data), accessed October 1, 2026
- U.S. Geological Survey, “Water Density,” accessed October 2, 2026: usgs.gov
- Electrical Safety Foundation International, “Outdoor Electrical Safety Check” booklet (2021): esfi.org
- LifeSmart LS100DX and AquaRest Discover Standard 400 listings (power), checked September 2026