One of the main reasons people switch from electric Jacuzzis to wood-fired hot tubs is the promise of lower running costs. With electricity prices fluctuating and the cost of living rising, the idea of heating your bath with a few logs seems financially attractive. But is it really as cheap as it sounds? Or are there hidden costs in water consumption, chemical treatments, and stove maintenance that add up over time?
In this detailed breakdown, we will crunch the numbers. We will look at the real-world cost of a “soak,” comparing the price of kiln-dried logs versus electricity, and factor in the hidden resource of “time.” Here is the honest truth about the economics of owning a wood-fired spa.
1. The Fuel Cost: Wood vs. Electricity
Let’s look at the physics. To heat 1,500 litres of water from 10°C (tap temperature) to 38°C (bathing temperature), you need approximately 50 kWh of energy.
Electricity Scenario:
At an average UK unit price of roughly £0.28 per kWh (variable), heating that water electrically would cost:
50 kWh x £0.28 = £14.00 per heat-up.
Plus, electric tubs run cleaning cycles and maintain heat 24/7, leading to monthly bills of £50-£100 depending on insulation.
Wood Scenario:
Dry hardwood (like birch or ash) provides about 4-5 kWh of heat energy per kg. Allowing for stove efficiency losses (heat escaping up the chimney), you might need roughly 15-20kg of wood to heat that same tub.
If you buy kiln-dried logs in bulk crates, the cost is approx. £0.30 – £0.50 per kg.
20kg x £0.40 = £8.00 per heat-up.
The Verdict: On a per-session basis, wood is roughly 40-50% cheaper than electricity if you buy wood at retail prices. If you have access to free wood (scavenged, seasoned branches, or bulk forestry waste), the cost drops to near zero.
2. The Cost of Water
Unlike electric tubs where water is kept for 3-4 months, wood-fired tubs often have simpler filtration (or none) and thus water is changed more frequently—perhaps every 2-4 weeks or even after every weekend use if no chemicals are used.
The Math: 1,500 litres is 1.5 cubic meters.
Average UK water cost (supply + sewage) is roughly £3.00 – £4.00 per cubic meter.
Cost to fill: £4.50 – £6.00.
If you change the water monthly, that’s £72 a year. If you change it weekly, that’s nearly £300 a year.
Tip: To reduce this, invest in a simple hang-on skimmer filter and use gentle sanitizers (like Active Oxygen) to extend water life to 6-8 weeks.
3. Consumables: Chemicals and Cleaning
Even a wood-fired tub needs hygiene.
– Sanitizers: Chlorine granules or bromine tablets. Annual cost: approx. £30-£50.
– Filter Cartridges: If using a filtration system, cartridges need replacing. Annual cost: £40-£60.
– Firelighters/Kindling: Don’t forget the start-up fuel. Annual cost: £20.
4. The Hidden Cost: Your Time
This is the intangible cost. An electric tub is ready instantly. A wood-fired tub requires:
– 15 mins to clean out ash and lay the fire.
– 2-3 hours of heating time (tending the fire every 30 mins).
– 30 mins to drain and clean the tub (if changing water).
If you value your time highly, this “labour cost” is significant. However, most owners view this time not as a cost, but as part of the leisure activity—a way to disconnect from work and be outside. It is “active relaxation” rather than a chore.
5. Maintenance and Depreciation
Wood-fired tubs have very low depreciation and maintenance compared to electric spas.
– No pumps to burn out.
– No circuit boards to fry.
– No heating elements to scale up.
The only real maintenance cost is treating the exterior wood with oil once a year (approx. £20 for a tin of oil) and potentially replacing the stove grate after a few years of heavy use (£50). A well-maintained wooden hot tub can last 15+ years with minimal spending.
Frequently Asked Questions (FAQ)
Can I use waste wood or pallets?
Yes, provided it is untreated (no paint/varnish) and dry. Pallet wood burns very fast and hot, so be careful not to over-fire the stove. Avoid painted wood as it releases toxic fumes and damages the steel.
Does an insulated cover save money?
Absolutely. Heating without a cover takes twice as long and uses twice as much wood. A cover pays for itself within one winter season in fuel savings.
Is it cheaper to keep it warm or heat from cold?
For wood-fired tubs, it is usually cheaper to heat from cold or “warm” (if used the previous day). Trying to keep a fire smouldering 24/7 is inefficient and creates too much smoke/tar. If you use it daily, the water will still be 25-30°C the next evening (with a good cover), requiring only a small top-up fire.
Conclusion
Financially, the wood-fired hot tub is the clear winner for anyone who uses their spa 1-3 times a week, especially if you have a cheap wood source. The lack of monthly electricity bills makes it a recession-proof luxury. The only real “cost” is your time—but spending time tending a fire and watching the stars is hardly a high price to pay.