Running a hot tub in a British winter is one of life’s genuine pleasures — there’s something magical about sitting in 38°C water while it’s 3°C outside. The problem is that without proper insulation, you’ll feel the magic mostly in your energy bills.
An uninsulated or poorly insulated hot tub can cost £80-150 per month to run during winter. A well-insulated one brings that down to £30-50. Over an October-to-March season, the saving is £300-600. That pays for most insulation projects in the first year. If you’re still choosing a hot tub, checking the insulation spec before you buy will save you this entire job.
Here’s how to do it properly, what works, what doesn’t, and the mistakes that end up costing more than they save.
Why Hot Tubs Lose Heat
Understanding where the heat actually goes helps you target your insulation efforts:
- Through the cover — this is the biggest source of heat loss by far. Hot water evaporates into the gap between the water surface and the underside of the cover. That evaporation carries enormous amounts of energy away. A damaged, waterlogged, or poorly fitting cover can account for 60-70% of total heat loss
- Through the cabinet walls — the side panels of most hot tubs are thin. Acrylic shells with air gaps behind them lose heat through conduction and convection
- Through the base — heat conducts downward into whatever the tub sits on. Concrete patios are particularly bad because they conduct heat efficiently
- Through pipes and plumbing — hot water sitting in exposed pipes loses heat, especially when the pumps aren’t running and the water is static
- Through the surface when uncovered — every minute with the cover off loses significant heat. In winter with wind, this is dramatic
Start with the Cover
Before you insulate anything else, check your cover. If it’s more than 4-5 years old, waterlogged (feels heavy when you lift it), cracked, or doesn’t sit flush against the rim, replacing it will save more energy than every other insulation measure combined.
What Makes a Good Cover
- Thickness — 4 inches (100mm) tapered to 3 inches (75mm) is the UK standard. Thicker is better for winter. Some suppliers offer 5-6 inch covers for harsh climates
- Foam density — higher density foam (1.5 lb/ft³ minimum) insulates better and resists waterlogging longer than cheap low-density foam
- Vapour barrier — the plastic sheet wrapped around the foam core must be intact and sealed. When this fails, steam penetrates the foam, the cover absorbs water, and insulation value drops noticeably
- Seal/skirt — the cover should sit flush against the rim with no gaps. Any gap lets warm, moist air escape. Some covers have a continuous skirt or lip that drapes over the edge for a tighter seal
- Hinge seal — the fold in the middle of the cover is a weak point. Better covers have a sealed hinge with insulated material in the fold
UK suppliers for replacement covers:
- Hot Tub Covers UK (hottubcoversuk.co.uk) — made to measure
- Penguin Hot Tub Covers — good mid-range option
- Cover Valet — premium covers with excellent seals
- Your hot tub manufacturer — often more expensive but guaranteed to fit
Expect to pay: £200-400 for a quality custom cover. It sounds a lot until you realise a waterlogged cover can add £40-60 per month to your energy bills.
Cover Lifters
A cover lifter isn’t insulation, but it’s relevant: people who struggle to remove their cover tend to leave the hot tub on longer before getting in, leave the cover half-off while entering, or delay using the tub altogether. A lifter (£80-150) makes cover management effortless, which means less heat loss during access and more actual use of the tub.
Insulating the Cabinet
The cabinet (the wooden or composite surround) is your next target. Most hot tubs have a shell (acrylic or rotomoulded), an air gap, some factory insulation, and then the cabinet panels. Improving what’s in that air gap makes a significant difference.
Full-Foam Insulation
Premium hot tubs come with the entire cavity between the shell and cabinet filled with polyurethane spray foam. This is the gold standard — it virtually eliminates convection within the cabinet, insulates every pipe and fitting, and adds structural rigidity.
If your tub came without full foam and you’re comfortable removing cabinet panels, you can retrofit spray foam. However:
- It makes future repairs extremely difficult. If a pump or pipe needs replacing, you’ll spend hours chipping through solid foam to access it
- Professional installation recommended — spray foam expands notably and can warp cabinet panels or stress plumbing fittings if applied incorrectly
- Cost: £150-300 professionally applied
Reflective Foil Insulation (DIY-Friendly)
Multi-layer reflective foil insulation (like Superfoil, ThermaWrap, or YBS BreatherQuilt) is the most practical DIY option. It’s thin, flexible, reflective, and easy to cut and staple into place.
How to install:
- Remove the cabinet panels (most are held with clips or screws)
- Cut foil insulation to fit between the shell and panel
- Staple or tape into place with the reflective side facing inward (toward the shell)
- Replace panels
The reflective surface bounces radiant heat back toward the tub, while the layered construction provides a thermal break. In our testing, reflective foil reduced cabinet heat loss by roughly 25-30% — not as effective as full spray foam, but easy to install, removable for repairs, and costs £30-50 in materials.
Rigid Foam Board
Kingspan or Celotex offcuts (25-50mm thick) can be cut to fit inside the cabinet cavity. They provide excellent insulation per millimetre and don’t absorb water.
Pros:
- High insulation value (better than reflective foil per unit thickness)
- Moisture-resistant
- Readily available from any Screwfix, Wickes, or B&Q
- Can be cut with a Stanley knife
Cons:
- Rigid — doesn’t conform to curved surfaces well
- Needs cutting precisely to fit around pipes and fittings
- Can be fiddly to install in tight spaces
Cost: £15-40 depending on coverage area. Many DIYers use leftover offcuts from home projects.
Pipe Lagging
While you’ve got the panels off, lag any exposed pipes with standard foam pipe insulation (available at any plumbing merchant or B&Q for a few pounds). Pay particular attention to:
- Pipes that run near the base or outside edges of the cabinet
- The pump connections where pipes carry hot water between the heater and jets
- Any pipe runs longer than 30cm
This is cheap (£5-10 for enough to do the whole tub) and takes 20 minutes. There’s no reason not to do it.
Insulating the Base
Heat loss downward is often overlooked. If your hot tub sits directly on a concrete patio or paving slabs, you’re losing heat into the ground continuously.
Base Insulation Options
Rigid foam board under the tub: The most effective solution. Place 25-50mm Celotex or Kingspan boards on the patio before positioning the tub. This creates a thermal break between the tub base and the cold ground.
Important: the tub must still sit on a flat, level, structurally sound surface. The Energy Saving Trust recommends insulating any surface where heat transfers to cold ground, and hot tub bases are no exception. Use foam board on top of concrete — never on soft ground where it could compress unevenly.
Hot tub base pad: Purpose-made insulating base pads are available online (£30-80). They’re essentially dense foam or rubber sheets cut to size. Less effective than rigid foam board but easier to install.
Interlocking foam tiles: Gym-style interlocking EVA foam tiles (£15-25 for a pack) work surprisingly well as base insulation. They’re waterproof, provide decent thermal resistance, and distribute weight evenly. Stack two layers for better performance.
Wooden deck: If your tub is on a raised deck, you’ve already got an air gap acting as insulation. The air space between the deck boards and the ground is surprisingly effective. No additional base insulation needed in most cases.
What NOT to Put Under a Hot Tub
- Carpet or fabric — traps moisture, grows mould, compresses under weight
- Gravel alone — provides almost no insulation
- Standard garden membrane — offers no thermal benefit
- Bubble wrap — compresses to nothing under the weight of a filled tub
Windbreaks and Shelter
Wind chill doesn’t just affect you while you’re sitting in the tub — it strips heat from the cabinet and cover surfaces too. A hot tub in an exposed, windy position costs noticeably more to run than one in a sheltered corner.
Effective Wind Protection
- Fencing or screening on the prevailing wind side (usually southwest in the UK). Doesn’t need to be solid — even slatted fencing reduces wind speed by 50-60%
- Hedging — an evergreen hedge (laurel, privet, or leylandii) provides year-round wind protection and looks better than fencing. Plant it 1-2 metres from the tub
- Gazebo or pergola with side panels — reduces heat loss from the cover surface by blocking wind and trapping a layer of still air above the tub
- Purpose-built hot tub enclosure — the most effective option but also the most expensive (£500-3,000+ depending on spec)
Positioning
If you haven’t installed your hot tub yet, think carefully about placement:
- Against a house wall (sheltered from wind, retains reflected heat)
- In a corner of the garden (natural wind shelter from two sides)
- Away from trees (falling leaves block filters and make a mess)
- Close to the house (shorter distance to run in a towel)
The Thermal Blanket Hack
A floating thermal blanket sits directly on the water surface, under the main cover. It’s a thin sheet of insulating material (usually closed-cell foam or a bubble-wrap style membrane) that creates an additional barrier against evaporation.
Why it works: Evaporation from the water surface is the single biggest source of heat loss. The cover traps some of that moisture, but there’s still a significant air gap between water and cover. A floating blanket eliminates that gap.
Cost: £15-40 depending on size. Many hot tub owners cut a standard pool solar blanket to size for under £15.
Effectiveness: Can reduce heating costs by 10-15% on its own. Combined with a good cover, it’s one of the cheapest and most effective insulation upgrades available.
The only downside is the slight hassle of removing it before each soak and replacing it after. Most people find it becomes habit within a week.
Putting It All Together
Here’s the priority order for maximum impact per pound spent:
- Fix or replace the cover — biggest single improvement (£0 if just fixing the seal, £200-400 for replacement)
- Add a floating thermal blanket — cheapest meaningful upgrade (£15-40)
- Lag exposed pipes — takes 20 minutes, costs £5-10
- Insulate the base — foam board or tiles (£15-40)
- Insulate the cabinet — reflective foil or rigid board (£30-50)
- Add wind protection — fencing, planting, or screening (£50-500+)
Total cost for a thorough DIY insulation job: £100-200. Annual saving: £300-600 in electricity during winter months. It pays for itself before Christmas.
Energy-Saving Tips Beyond Insulation
A few operational habits that complement your insulation work:
- Drop the temperature by 1-2°C when not in use — even 36°C to 34°C saves meaningful energy. Reheating 2°C takes 30-60 minutes depending on your heater
- Use a timer — heat the tub to full temperature before your usual soak time, not 24/7
- Keep the cover on — every minute uncovered costs heat. Put it back on even if you’re getting out for 10 minutes to refill drinks
- Clean filters regularly — dirty filters restrict flow, making the pumps work harder and longer
- Consider an air source heat pump — for tubs used year-round, a dedicated ASHP can reduce heating costs by 60-75%. Upfront cost is £500-1,500 but the running cost savings are substantial
The Bottom Line
Insulating a hot tub for winter isn’t glamorous work, but it’s some of the most cost-effective DIY you’ll ever do. A Saturday afternoon with some foil insulation, pipe lagging, and a floating blanket can save you hundreds of pounds every winter — and make the tub heat up faster, hold temperature longer, and run quieter (because the heater cycles less).
The British winter is long and dark. A hot tub makes it bearable. Proper insulation makes it affordable.
Insulation Materials Compared: What UK Hot Tub Owners Actually Use
After speaking with dozens of hot tub owners across UK forums and local groups, we found some clear patterns in what works best for British conditions. The key factor most people overlook is moisture resistance — our damp climate means any insulation material needs to handle condensation without degrading.
Closed-cell spray foam remains the top performer, but it’s a permanent commitment. If you’re handy with DIY and want something reversible, 50mm Celotex boards cut to shape and held in place with foil tape offer roughly 80% of the performance at 20% of the cost. We found that combining rigid board on the largest flat surfaces with reflective foil wrapped around pipes and awkward curves gives the best balance of effort to reward.
One option worth considering for older tubs is an external thermal jacket — essentially a fitted insulating wrap that goes around the entire cabinet exterior. Companies like Hot Tub Suppliers and Arctic Spas sell these for £100-200. They’re not as effective as internal insulation but require zero disassembly and can be fitted in ten minutes. For anyone who doesn’t fancy removing cabinet panels, it’s a decent compromise.
Whatever material you choose, pay attention to the joins and gaps. We’ve seen tubs with excellent panel insulation but 5cm gaps at every corner where cold air flows freely in and out. Seal those gaps with expanding foam or self-adhesive foam strip (£3-5 from any hardware shop) and you’ll notice the difference immediately in how often the heater kicks in overnight.