A stock tank pool is brilliant on a hot afternoon, but out of the box it’s a big galvanised trough of whatever temperature the weather gives you. If you want to use it in spring and autumn, or turn it into a proper hot soak, you need a stock tank pool heater, and the right one depends on how warm you want the water and how much you’re prepared to spend running it.
Here are the realistic options, with the numbers behind each, so you can see what will work before you buy anything.
The short version
- Decide on the temperature first. A warm pool and a hot tub are very different jobs.
- Cover and insulate first. It makes the biggest difference to running costs, whatever heater you choose.
- For hot tub temperatures, a 3–4kW spa pack heater on a dedicated circuit is the reliable answer. Solar and plug-in heaters suit a summer pool.
First, decide what you’re heating to
Most people want one of two things:
- A warmer cool-dip pool. Water at roughly 80–85°F (27–29°C), so you can use it for longer each year.
- A stock tank hot tub. Water at 100–104°F (38–40°C), ready when you want it, all year round. That needs a properly sized heater, filtration and an insulated tank. I’ve covered the full build in how to build the ultimate DIY stock tank hot tub.
How much heat does a stock tank need?
Water takes a predictable amount of energy to warm up: about 1kWh for every 860 litres (227 US gallons) per 1°C. Using the same fill levels as my stock tank build guide (about 20in / 50cm of water), here’s the best case, before any heat is lost while it warms:
| Tank (filled to ~20in / 50cm) | Raise by 10°C (18°F) | Raise by 25°C (45°F) |
|---|---|---|
| 6ft round, ~1,250 litres (330 US gal) | ~14.5kWh (about £3.80 / $2.70) | ~36kWh (about £9.60 / $6.70) |
| 8ft round, ~2,270 litres (600 US gal) | ~26kWh (about £7.00 / $4.80) | ~66kWh (about £17.40 / $12.10) |
Costs use the UK price cap rate for October–December 2026 (about 26p per kWh) and a US average of about 18¢ per kWh in autumn 2026. Your tariff will be different, and prices vary a lot by region and state, so plug in your own rate.
That’s just the first heat-up. After that, the heater only has to replace what’s lost, and on an uncovered steel tank that’s a lot.
Option 1: a cover (do this whatever else you choose)
Most heat leaves through the water surface. The US Department of Energy says evaporation is by far the largest source of energy loss from a pool, and that a pool cover can cut heating costs by 50–70%.
- Bubble (solar) cover. Cheap, cut to size with scissors, and it lets a bit of sunshine through to warm the water. Fine for a summer pool.
- Insulated hard cover. Essential for hot tub temperatures.
The sides and base matter too. Steel conducts heat very well, so box the tank in with timber cladding, fill the gap with rigid foam board, and stand it on insulation board. There’s more on materials in DIY hot tub insulation.
A cover on this makes a massive difference in the heating costs as most of the heat is lost vertically of course!
Option 2: solar heating mats or panels
Solar collectors are black plastic mats or panels. Your filter pump pushes water through them and the sun warms it.
The DOE’s rule of thumb is a collector area of 50–100% of the pool’s surface area, depending on your climate. An 8ft (2.4m) round tank has a surface of roughly 50 sq ft (4.7m²), so you’re looking at around 25–50 sq ft (2.3–4.7m²) of collector, facing the sun and ideally angled towards it.
Good for: stretching the season on a cool-dip pool in a sunny spot.
Not good for: hot tub temperatures, cloudy weeks, evenings or winter. You get the heat when the sun shines, not when you want a soak.
If you want to go further with solar, I’ve looked at panels, batteries and heat pumps in what is the best way to heat a DIY hot tub.
Option 3: a small plug-in electric pool heater
These are inline resistance heaters made for small above-ground pools. Water from your filter pump goes through them and over an element. They’re cheap to buy, but every kilowatt of heat costs a kilowatt of electricity, and the power you can get from a plug is limited:
- USA: a standard 120V, 15A circuit tops out at about 1.8kW, so 120V pool heaters are small, often around 1–1.5kW.
- UK: a 13A plug tops out at about 3kW. Small 230V pool heaters are commonly around 2–3kW.
Do the maths with the table above. Raising an 8ft tank by 10°C (18°F) needs about 26kWh, so a 1.5kW heater needs roughly 17–18 hours of best-case running, and a 2.2kW heater about 12 hours. Fine for a summer pool, painfully slow for a hot tub.
If you go this way, buy one made for pool water, check the flow rate it needs from your pump, and use an outdoor-rated RCD (UK) or GFCI (USA) protected outlet.
Option 4: a spa pack heater (the proper hot tub route)
If you want a stock tank that’s hot when you want it, this is the answer. A spa pack combines the heater, controls and filtration schedule in one box. In my complete stock tank kits it’s a 4kW Balboa unit for the USA and 3kW for the UK and Europe, with the pump, a 25 sq ft cartridge filter and the fittings matched to it. If you only want warm, clean water without jets, the heating and filtration only kit is $1,399 at the time of writing.
From cold, a 4kW heater takes about 9 hours to raise a 6ft tank by 25°C (45°F), and about 17 hours for an 8ft tank. Again, that’s best case. Once it’s up to temperature and covered, it only has to top up the losses.
The electrics are not a DIY job. In the USA it’s a dedicated 240V GFCI-protected circuit with a disconnect, and spas come under NEC Article 680, including the bonding rules for metal parts, which matter with a steel tank. In the UK it’s a dedicated circuit with RCD protection, and a new circuit is notifiable work. Use a qualified electrician, and check your local regulations and permit rules. My guide to hot tub electrics explains the principles.
If your tank layout isn’t standard, or you want to add a heat pump or more jets later, my Tub & Pool Designer Pro plumbing design service will draw up the pipework and equipment for your tank, so the heater, pump and filter all work together.
Option 5: a small air source heat pump
A heat pump pulls heat out of the air, so in warm weather it delivers several kilowatts of heat for every kilowatt it uses. That makes it the cheapest heater to run, especially at pool temperatures.
The trade-offs: it costs more to buy, heats more slowly, and loses efficiency as the air gets colder. For a hot tub used through the winter, the common set-up is a small heat pump doing most of the work, with the spa pack’s heater as back-up. Size it for your tank volume and the coldest month you want to use it in. As with any heater, the electrical connection needs a qualified electrician.
Option 6: wood-fired and gas heaters
Wood-fired
A submersible stove sits in the water; an external one heats water through a jacket or coil. Both work off-grid, but you light the fire and wait, so there’s no quick dip after work. Keep flames and flues away from bare galvanised steel, guard anything hot that bathers could touch, and follow the stove maker’s instructions to the letter.
Gas or propane
Gas heaters are fast and suit people with gas on site. In the UK, gas work must be done by a Gas Safe registered engineer; in the USA, by a licensed gas fitter, to local codes. Use an outdoor-rated heater with the right clearances, because carbon monoxide is a real risk.
What never to use
- Livestock tank de-icers and floating heaters. They’re designed to stop drinking water freezing for animals, not to heat water people sit in.
- Bucket or immersion heaters. An unprotected element in water with people in it is dangerous.
- Extension leads, or anything without RCD/GFCI protection.
Stock tank pool heater options compared
| Option | Best for | Speed | Running cost | Watch out for |
|---|---|---|---|---|
| Cover and insulation | Everyone | n/a | None | Doesn’t add heat on its own |
| Solar mats or panels | Summer pool, sunny site | Weather-dependent | Pump only | No heat on demand |
| Plug-in electric | Taking the chill off a small tank | Slow | High per degree | Plug power limit, flow rate |
| Spa pack (3–4kW) | Stock tank hot tub | Medium | Medium to high | Dedicated circuit by an electrician |
| Air source heat pump | Lowest running cost | Slow to medium | Low | Higher upfront cost, weaker in cold weather |
| Wood or gas | Off-grid, or gas on site | Wood slow, gas fast | Varies | Fire, flue and CO safety |
Don’t forget the tank itself
Warmer water is harder on a stock tank. The American Galvanizers Association notes that warmer water attacks zinc more, so a heated galvanised tank needs protected cut edges, balanced water and no salt system. If you’re looking at a poly tank, check the maker’s temperature rating before you heat it to hot tub temperatures.
Which would I choose?
For a summer cool-dip pool, I’d start with a cover and add solar mats if the tank gets plenty of sun. For anything you want to use as a hot tub, I’d go straight to a spa pack, an insulated hard cover and insulated sides, and add a small heat pump later if running costs bother you.
Want a stock tank that’s hot when you want it?
My complete stock tank kits include the Balboa spa pack, pump, filter, fittings and a full DIY guide, so the heater and plumbing are matched from day one. If you’d rather build something permanent, my CAD-drawn hot tub plans come in 21 sizes, and I’ve helped 1,500+ customers with their builds.
FAQs
What is the best stock tank pool heater?
It depends on the temperature you want. For a summer pool, a cover and solar mats are cheapest to run. For hot tub temperatures, a 3–4kW spa pack heater on a dedicated circuit, ideally helped by a heat pump, is the reliable option.
Can I heat a stock tank pool with a 120V heater?
You can take the chill off a small tank, but a 120V circuit limits you to about 1.5kW. Raising an 8ft tank by 10°C (18°F) would take well over half a day, before heat losses.
Can I use a livestock tank de-icer to heat my stock tank pool?
No. De-icers are made to stop drinking water freezing for animals, not to heat water people bathe in. Use a heater designed for pools or spas, installed with the right electrical protection.
Does heating a galvanised stock tank make it rust faster?
Warmer water does wear the zinc coating faster. Protect cut edges, keep the water balanced, avoid salt systems and consider a liner or immersion-grade coating.
Heating your own stock tank? Tell me what you’re using in the comments below.
Cheers,
Andi