Solar for hot tubs

The heater is the whole story. A residential tub heater draws 4–6 kW while heating, and the circulation pump and jets add a few hundred watts to a couple of kilowatts when running. But the heater does not run continuously; it cycles to hold the set temperature, and how often it cycles depends on the outdoor temperature, the cover, the tub’s insulation, and how much you use it. Many owners see roughly 100–250 kWh a month averaged over the year, with winter months running well above that and summer months well below.

Over a year, that is on the order of 1,500–3,000 kWh — about the same as an electric vehicle driven a modest number of miles, or a single-speed pool pump over a season. It is a real load, and it shows up on the bill as a step change the month the tub is filled, but it is not the kind of load that requires rethinking the whole house.

Heat loss scales with the temperature difference between the water and the air. A tub held at 102°F loses far more heat on a 5°F Denver night than on a 60°F July evening, and at 8,000 feet in the mountains the nights are colder still and the season longer. Wind across the cover adds to it. That is why a hot tub’s electric use in December and January can be two or three times its use in July.

Unfortunately winter is also when Colorado panels produce the least: shorter days, lower sun angle, and snow on the array. Net metering under C.R.S. 40-2-124 in Xcel and Black Hills territory is what makes the numbers work — surplus credits earned in summer carry forward and offset the winter tub. In co-op or municipal territory with an annual true-up, the carryover may be worth less; the answer there is to size a little more conservatively.

A well-fitted, thick insulating cover is the cheapest upgrade. A worn or waterlogged cover can quietly double the heater’s run time. Lowering the set temperature a couple of degrees when the tub is not in daily use helps too, though most owners prefer to just size the solar for the habit they actually have.

Take the tub’s annual use, typically 1,500–3,000 kWh, and divide by what a well-placed Colorado kilowatt of panels produces, roughly 1,300–1,600 kWh a year. That is 1–2.3 kW of additional array, or three to six panels at 400–440 W apiece — about 60–120 square feet of roof. At our $2.80–$3.25 per watt residential pricing, the tub’s share of a system is roughly $3,000–$7,500 before any incentives.

If you are adding a tub to a home that already has our solar, the question is whether the existing array has surplus. A system sized in 2022 with a 20% margin may already cover it. If it does not, we can add panels if the inverter and roof allow; adding to systems installed by other companies is not something we do. The electrification calculator estimates the extra panels for a tub alongside any other new electric loads.

On Xcel’s residential time-of-use plan, weekday electricity from 5 to 9 pm costs about 2.7 times the off-peak rate — and 7 pm on a January weeknight is exactly when many people use a hot tub, with the cover off and the heater working hardest. You cannot fully move that; a tub in use needs its heater. What you can do is set the filtration and heating cycles to run in the early afternoon so the tub is fully up to temperature before 5 pm, and let it coast on stored heat through the evening.

This is also why a hot tub does not justify a battery on its own. Its evening on-peak use is real but modest, and a battery large enough to matter costs far more than the on-peak premium on a tub. If you want a battery for backup or to cover the whole house from 5 to 9 pm, the tub rides along; if the tub is the only reason, skip it.

Most tubs need a dedicated 240-volt circuit, typically 50 amps with a GFCI disconnect within sight of the tub, run by an electrician under a permit. That circuit takes space and capacity in your main panel. Homes with 100-amp service that already have an electric range, dryer, and an EV charger can run out of room, and adding solar has its own breaker requirements. We look at the panel before quoting so that the tub, the array, and any charger all fit — or so we can tell you a panel upgrade or a load-management device is part of the job.

If the tub and the solar are going in around the same time, do them together: one permit visit for the electrical work, one trench or conduit run if the tub is away from the house, and a system sized for the house you will actually be living in.