Why electric heating can't warm the hot tub in winter – and what it can do instead

It's Friday evening, shortly after 6 p.m. The work week is over, and dusk is already falling. You look through the patio door into your garden – there it is, your hot tub.

The electric heating has been running since noon today.

The display should have shown 38 degrees long ago.

Enough for a relaxing evening under the stars, perhaps with a beer in hand.

But the thermometer reads 28 degrees. Or worse: 26.

They check the fuse. Everything's fine. They touch the water – lukewarm, nothing more. The heater hums, the indicator light is green. No fault. And yet: the water simply won't get hot.

It's 5 degrees outside. A clear, cold November evening. Exactly the kind of weather you bought the hot tub for.

You are not alone – and it is not a defect

We are familiar with this situation. Every year, as soon as the first frost arrives, we receive exactly these inquiries: "The electric heater isn't heating properly anymore. Is it broken?"

The answer is as frustrating as it is honest: No, it's not broken. It's doing exactly what it's physically capable of – and that's a very limited amount in winter.

This has nothing to do with the quality of the heater. It also has nothing to do with your hot tub. It's simply physics. The hard, uncompromising kind of physics that even the best technology can't overcome.

But – and this is the good news – if you understand why the 3kW electric heater gives up in winter, you also know what it's made for. And then the supposed "weakling" becomes a damn useful tool.

What you will learn in this article

I could tell you now that the electric heating is "perfectly adequate"—but that would be a lie. Instead, as a tradesman to tradesman, let me explain what's really going on here:

• Why 3 kilowatts of heating power are lost to the cold in winter (with figures you can understand)
• What electric heating can realistically do – and what it can't (without sugarcoating)
• How to cleverly combine wood stove and electric heating (the hybrid strategy used by 80% of our customers)
• When an electric heater is really worth it (spoiler alert: it's worth its weight in gold as frost protection)

By the end of this article, you will know exactly whether a 3kW electric heater is suitable for your situation – or whether you need a different solution.

No sales pitches. No false promises. Just the facts you need to make the right decision.

Let's begin.

➡️ Book a free hot tub consultation

The bucket with holes: How heat works in a hot tub

Forget about all the technical data sheets for a moment. Instead, imagine this:

Their hot tub is a bucket. A large bucket containing 1,600 liters of water. And this bucket has holes.

The heater is like the tap that refills with water at the top. The holes in the bottom and sides allow water to drain out. Their sole purpose: to maintain the water level – or better yet, to increase it.

Sounds easy, right?

Now we'll adjust a few things:

• The holes get bigger the colder it is outside.
• The water flow from the tap remains the same (your 3kW heater).
• The bucket is huge (1,600 liters = 1.6 tons of water)

And suddenly, a simple problem becomes a battle you cannot win.

Welcome to the reality of thermodynamics.

The three players in this game

To understand why electric heating reaches its limits in winter, we need to know three factors. All three work against each other – and one of them is the absolute killer.

Player 1: The Mass – Why Water Is So Inert

Water is a fantastic heat reservoir. That's good if you want your hot tub to still be warm in the evening. That's bad if you want to heat it up.

The number you need to know: 1.16 watt-hours per kilogram and degree.

This means that to heat 1 kilogram of water by 1 degree Celsius , you need 1.16 watt-hours of energy . This is a natural constant. You can't change it.

Their hot tub holds 1,600 liters of water. That's 1,600 kilograms. Almost two tons.

Example calculation: To heat these 1,600 liters by just 1°C :

• 1,600 kg × 1.16 Wh = 1,856 watt hours = 1.86 kWh

That's more than a kettle uses to boil water 10 times.

And now for the kicker: your 3kW heater delivers 3 kilowatt hours per hour. That means, purely theoretically – in a perfect world without heat loss – it would heat the water by 1.6°C per hour .

That doesn't sound so bad, does it?

This is where player 2 comes into play.

Player 2: The temperature difference – The pressure to lose

Heat is lazy. It only ever wants one thing: to equalize. To move from warm to cold until everything has the same temperature. That's the second law of thermodynamics, and it's merciless.

The greater the temperature difference, the stronger the urge.

An example:

• Their water: 30°C
• The outside air temperature: 5°C
• Difference: 25 degrees

It's like putting a hot pot on a sheet of ice. The pot wants to cool down. And it does. Permanently.

The hot tub loses heat in three ways:

1. Transmission (through the walls and the floor)

   • Wood insulates quite well, but it's not polystyrene.
   • Loss: low to medium (approx. 200-400 watts with the lid closed)

2. Convection (the wind blows across the water)

   • The stronger the wind, the more heat is "carried away".
   • Loss: medium (approx. 300-600 watts, increases with wind speed)

3. Evaporation (water turns into steam)

   • This is the killer. And he is brutal.

Player 3: Evaporation – The invisible energy drain

Things are about to get physical – but stay with me, it's worth it.

When water evaporates, it takes energy with it. A lot of energy.

To convert 1 liter of water from liquid to steam, you need 627 watt-hours . This is the so-called latent heat of vaporization . That's 340 times more energy than you need to raise the temperature of water by 1 degree.

Let that sink in: 340 times more.

That's why you sweat when you're hot. The sweat evaporates and cools your skin – because it draws energy from the skin.

And that's exactly what happens on the surface of your hot tub.

When the lid is open:

• Warm water (30°C) meets cold air (5°C)
• The air above the water is relatively dry (winter days usually have low humidity).
• Water constantly evaporates – drawing enormous amounts of energy from the remaining water in the process.

The figures: A hot tub with a diameter of approximately 2 meters has a surface area of ​​about 3.14 square meters .

At a water temperature of 30°C and an outside temperature of 5°C (a 25-degree difference), this surface loses the following amount of water through evaporation:

• Approximately 800 watts per square meter (rule of thumb for open water surfaces)
• Total: 3.14 m² × 800 W/m² = approx. 2,500 watts = 2.5 kW

And that's when there's no wind . With wind, the value rises to 3-4 kW or more.

Your 3kW heater delivers: 3 kW. The loss due to evaporation consumes: 2.5-4 kW.

Do you see the problem?

The bottom line: Why the bucket runs dry

Now we'll put all the players together. Imagine you're sitting in a hot tub. The lid is open (obviously, you want to bathe). It's 5°C outside. A light breeze is blowing.

What happens:

What goes in?	What's going out	Net
+3.0 kW (heating)	-2.5 kW (evaporation)	+0.5 kW
	-0.4 kW (Transmission)
	-0.3 kW (convection)
Total: +3.0 kW	Total: -3.2 kW	-0.2 kW

Result: The water cools down, despite the heating being on.

Not quickly – maybe 1-2 degrees per hour. But it's cooling down. You're sitting in the tub, the heater is struggling, and you're slowly getting cold.

This is not a malfunction. This is physics.

And what about a closed lid?

Ah, this is where the game changes completely.

A good, insulated thermal lid reduces evaporation by 80-90% . Suddenly, the balance looks like this:

What goes in?	What's going out	Net
+3.0 kW (heating)	-0.3 kW (evaporation, reduced)	+2.5 kW
	-0.2 kW (Transmission)
Total: +3.0 kW	Total: -0.5 kW	+2.5 kW

Result: The water heats up. Slowly, but steadily.

With 2.5 kW net power you can achieve:

• Temperature increase of approximately 1.3°C per hour
• Or: Maintain temperature overnight with already warm water

The lid is not optional. It is the difference between success and failure.

Summary: The bucket with the holes

Here's what you need to remember:

✅ The heater (3 kW) is the tap – it refills, but only with a limited flow rate.

✅ The mass (1,600 liters) is inert – heating water requires a lot of energy (1.86 kWh per degree)

✅ The temperature difference (25 degrees) is the pressure – the greater the difference, the faster the bucket empties.

✅ Evaporation is the biggest drain – it consumes 2.5-4 kW when the lid is open.

✅ The lid is your lifeline – it plugs the holes and gives the heater a chance.

The electric heater doesn't lose because it's weak. It loses because its opponent – ​​the winter cold – is simply too strong.

But – and this is crucial – she doesn't even have to win this fight. She's built for something else. And she's really good at it.

We'll take a look at exactly what that is now.

What a 3kW electric heater can really do – the honest calculation

Now we're getting down to specifics. No more metaphors, no more theoretical calculations. Now we'll calculate what your 3kW electric heater can actually achieve in practice – and where it falls short.

As a tradesman, you know: numbers don't lie. So let's look at the numbers.

Scenario 1: Winter, lid open – The hopeless fight

The situation:

• Outside temperature: 5°C
• Water temperature: 30°C (already preheated, e.g. with a wood stove)
• They want to take a bath, the lid is open
• Wind: light breeze (2-3 Beaufort, nothing extreme)

What the heating system does:

• +3.0 kW constant heating output

What you lose:

• Evaporation: -2.5 kW (in calm conditions) to -3.5 kW (in windy conditions)
• Transmission (through wooden walls/floor): -0.3 kW
• Convection (wind over water surface): -0.4 kW
• Total: -3.2 to -4.2 kW

The result:

 +3,0 kW (rein) - 3,2 kW (raus) = -0,2 kW

Result: The water cools down. You lose approximately 0.1-0.3°C per hour, depending on the wind.

After two hours of swimming at 5°C outside:

• Start: 30°C
• End: 29.4-29.7°C

It feels like: "The heating isn't doing anything."

And frankly, in this scenario, that's true. The heating system is fighting, but it's losing. It's only delaying the cooling, not stopping it.

Scenario 2: Winter, lid closed – The patient winner

The situation:

• Outside temperature: 5°C
• Water temperature: 20°C (e.g. after a few days of non-use)
• Lid is closed (good thermal lid, insulated)
• They want to heat the water overnight.

What the heating system does:

• +3.0 kW constant heating output

What you lose:

• Evaporation: -0.2 kW (almost zero due to the lid)
• Transmission: -0.3 kW
• Total: -0.5 kW

The result:

 +3,0 kW (rein) - 0,5 kW (raus) = +2,5 kW Netto

Result: The water heats up. With 2.5 kW net output, you can achieve:

Heating speed:

• 1,600 liters require 1.86 kWh per degree.
• At 2.5 kW net power: 1.86 kWh ÷ 2.5 kW = 0.74 hours = approx. 45 minutes per degree

Specifically:

• From 20°C to 30°C (10 degrees): approx. 7-8 hours
• From 25°C to 35°C (10 degrees): approx. 7-8 hours

This means that if you turn on the heating at 10 pm (with the lid on), you'll have about 8-9 degrees more temperature by 6 am. Not fast, but it works.

It feels like: "Slow but steady. I can work with that."

Scenario 3: Summer, lid open – Relaxed operation

The situation:

• Outside temperature: 20°C (beautiful summer evening)
• Water temperature: 32°C
• They are bathing, the lid is open
• Wind: hardly any

What the heating system does:

• +3.0 kW

What you lose:

• Evaporation: -0.8 kW (much lower, because the temperature difference is only 12 degrees)
• Transmission: -0.2 kW
• Convection: -0.2 kW
• Total: -1.2 kW

The result:

 +3,0 kW (rein) - 1,2 kW (raus) = +1,8 kW Netto

Result: The water even warms up while bathing. Approximately +1°C per hour.

It feels like: "Perfect. The heating system is doing exactly what it's supposed to."

Scenario 4: Antifreeze, lid closed – The bodyguard mode

The situation:

• Outside temperature: -5°C (frosty night)
• Water temperature: 8°C (You are not currently using the tub, but want to avoid frost damage)
• Lid closed
• Thermostat set to 10°C

What the heating system does:

• +3.0 kW (when thermostat is active)

What you lose:

• Evaporation: -0.1 kW (virtually zero)
• Transmission: -0.4 kW (larger difference compared to the outside temperature)
• Total: -0.5 kW

The result:

 +3,0 kW (rein) - 0,5 kW (raus) = +2,5 kW Netto

Result: The heating system easily keeps the water above 0°C . The thermostat only switches on occasionally (perhaps 2-3 hours per day at -5°C outside); the rest of the time the insulation is sufficient.

Power consumption:

• Approx. 6-9 kWh per day in permanent frost
• At 0.35 €/kWh: approx. 2-3 € per day
• Per month: approx. €60-90 (in case of continuous frost, worst case)

It feels like: "I'm relieved. The hot tub is safe, no frost damage."

The comparison table – everything at a glance

Here is the overview that you should print out and hang on the garden gate:

scenario	Outside temp.	Lid	Heating output	Loss	Net	Result	Practical benefits
Winter, Baden	5°C	Open	+3.0 kW	-3.2 kW	-0.2 kW	Water cools down (approx. 0.2°C/h)	❌ The heating system can't handle it
Winter, heating	5°C	To	+3.0 kW	-0.5 kW	+2.5 kW	Water heats up (approx. 1.3°C/h)	✅ It works, but requires patience
Summer, bathing	20°C	Open	+3.0 kW	-1.2 kW	+1.8 kW	Water heats up (approx. 1°C/h)	✅ Heater maintains temperature
Antifreeze	-5°C	To	+3.0 kW	-0.5 kW	+2.5 kW	Water remains above 0°C	✅ Perfect for frost protection

What does that mean for you?

Let's be honest: The 3kW electric heater is NOT a replacement for a wood stove in winter.

But – and this is important – it wasn't built for that.

Here's what it's made for:

✅ She's GOOD at this:

1. Frost protection (main task!)

• Reliably keeps water above 0°C, even at -10°C outside.
• Thermostat regulates automatically, no babysitting required.
• Prevents costly frost damage to pipes, pumps, wood
• Costs: Approx. €50-90/month in winter (depending on insulation and temperatures)

2. Maintain temperature (with lid closed)

• After heating with a wood stove: Retains 35°C overnight
• They heat with wood to 38°C on Saturday → Sunday morning still 34-36°C
• Ideal for "standby operation" between swimming days
• Advantage: You don't have to heat it up from scratch every time.

3. Summer operation (April to September)

• At outside temperatures of 15-25°C, it is sufficient as the ONLY heat source.
• It takes 8-12 hours to heat up (overnight), but it works.
• Perfect for spontaneous summer evenings
• Cost: Approx. €20-40/month

❌ She CAN'T do this:

1. Heating up in winter (from cold to warm)

• From 10°C to 38°C with an outside temperature of 5°C: Takes 20+ hours or fails.
• Physically pushed to the limit, every breath of wind throws you back.
• That's what the wood stove is for (20-40 kW output = 10x more powerful)

2. Maintain temperature while bathing (lid open, winter)

• Evaporative cooling consumes all the power.
• Water cools down despite heating (1-2°C per hour)
• They're slowly getting cold, the electricity bill is rising.

3. Heat large quantities of water quickly

• 1,600+ liters is simply too much mass for 3 kW.
• Like stirring a swimming pool with a teaspoon

The crucial comparison: electric vs. wood stove

To give you a sense of the dimensions:

3kW electric heater:

• Power: 3,000 watts
• Heating 1600L by 10°C: approx. 7-8 hours (with lid, winter)
• Cost per heating cycle: approx. €6-7 (at €0.35/kWh)

Typical wood-burning stove (integrated):

• Power: 25-40,000 watts (yes, really!)
• Heating 1600L by 10°C: approx. 1-2 hours
• Cost per heating cycle: approx. €5-8 (depending on the price of wood)

The wood-burning stove isn't "a little more powerful." It's 10-15 times more powerful.

That's the difference between a hand drill and a hammer drill. Both have their uses, but for some jobs you simply need power.

Interim conclusion: Electric heating is a tool, not a miracle.

If you're disappointed now – I understand. Many customers think when buying: "3 kilowatts sounds like a lot, that will be enough."

But here's the truth:

The 3kW electric heater is not too weak. It is specialized.

It's the frost protection bodyguard . It's the temperature maintainer . It's the summer solution .

But it is not your winter power plant .

And that's okay. Because if you use it correctly – in combination with a wood-burning stove or as a stand-alone unit in the summer – then it does its job perfectly.

In the next section, I will show you exactly what that looks like.

Wood stove + electric heating: How to get the best of both worlds

Now comes the part you've been waiting for: The solution.

You've seen that electric heating alone reaches its limits in winter. And you probably also know that running a wood-burning stove all winter is neither practical nor economical.

The answer is not an "either-or". It is a "both-and".

Welcome to the hybrid strategy – the setup used by over 80% of our customers in Baden-Württemberg and Bavaria.

The principle: division of labor like on a construction site

Imagine you're renovating a house. For some jobs you'd use a sledgehammer (fast, powerful, loud). For others, a file (precise, patient, quiet).

It's the same with the hot tub:

• The wood stove is your sledgehammer

  • Delivers raw power (25-40 kW)
  • Heats up quickly (1-3 hours from cold to hot)
  • It's fun, it's an experience
  • Requires your attention (adding wood, checking the fire)

• The electric heater is your file.

  • Works in the background (3 kW constant)
  • Does the temperature remain stable for days?
  • Requires no attention (thermostat regulates)
  • Protects against frost if you are away for two weeks.

The secret: They don't have the two work against each other, but one after the other .

The hybrid workflow – step by step

This is what a typical winter weekend with a hybrid system looks like:

FRIDAY, 4:00 PM – The wood-burning stove takes over

They come home from work. The hot tub is at 12°C (the electric heater kept the frost protection going, but no longer).

What you do:

1. Lid off
2. Light the wood stove (kindling, then add more logs)
3. Set the electric heater thermostat to 36°C (it runs in parallel)

What happens:

• Wood-burning stoves deliver 30-40 kW heating power
• Electric heating provides an additional 3 kW
• Together: 33-43 kW = an absolute powerhouse

Result after 2-3 hours (approx. 7:00 PM):

• Water temperature: 38°C
• The wood stove is completely glowing hot, the fire goes out.
• Electric heating now takes over

They enjoy:

• 7:00 PM - 9:00 PM: Swimming in 38°C warm water
• The fire is still flickering slightly, perfect atmosphere.
• Starry sky, beer, relaxation

FRIDAY, 9:00 PM – The electric heating takes over the night shift

They get out of the tub. Water temperature: still 36°C (slightly cooled by bathing).

What you do:

1. Put the lid on (IMPORTANT!)
2. Electric heating continues to run (thermostat set to 36°C)
3. They go to bed

What happens overnight:

• Outside temperature drops to 2°C
• With the lid closed: loss only approx. 0.5 kW
• Electric heater delivers 3 kW
• Net: +2.5 kW = Temperature remains stable or rises slightly

Result on Saturday morning, 8:00 a.m.:

• Water temperature: 34-36°C
• Only 0-2 degrees loss over 11 hours of night
• Without the electric heating: The water would be at 20-25°C (15 degree loss!)

SATURDAY, 10:00 AM – A quick top-up of heating is sufficient

They want to take another bath. The water temperature is 34°C.

What you do:

1. Briefly heat the wood stove (30-45 minutes)
2. From 34°C to 38°C = only a 4-degree difference
3. Complete.

Result:

• Minimal wood consumption (maybe 3-4 logs)
• Fast heating (only 30-45 minutes instead of 2-3 hours)
• They have more time for bathing, less for heating.

SUNDAY & MONDAY – Electric heating in solo mode

They no longer use the tub over the weekend. But they want to again next weekend.

What you do:

1. Set the thermostat to 10°C (frost protection mode)
2. Lid
3. Complete.

What happens:

• Electric heater keeps water at 10°C
• Only switches on when the temperature drops below 9°C
• Electricity consumption: approx. 5-8 kWh/day = €1.50-2.50/day
• No frost, no stress, no damage

Results next Friday:

• Water is at 10°C (instead of frozen)
• They heat with wood again → the cycle begins anew.

The costs – honestly calculated

Now comes the question every tradesman asks: "How much will this cost me?"

Here is the complete calculation for a winter month (December, January, February) with 2 baths per week :

Wood consumption:

Per heating session (Friday, from 12°C to 38°C):

• Burning time: approx. 2.5 hours
• Quantity of wood: approx. 15-20 kg beech wood (well dried)
• Cost: approx. €5-7 (at 30-35 cents/kg wood, regional Baden-Württemberg/Bavaria)

Per reheating session (Saturday, from 34°C to 38°C):

• Burning time: approx. 30-45 minutes
• Amount of wood: approx. 5-8 kg
• Cost: approx. €2-3

Per week:

• 1x main heating + 1x reheating = approx. €7-10

Per month (4 weeks):

• €28-40 for wood

Electric heating power consumption:

Frost protection mode (5 days/week when not in use):

• Approximately 6-8 kWh/day at 0°C outside
• 5 days × 7 kWh = 35 kWh/week
• Costs: 35 kWh × 0.35 €/kWh = 12.25 €/week

Maintaining temperature (2 nights/week after bathing):

• Approx. 10-12 kWh/night (maintains 35°C with the lid closed)
• 2 nights × 11 kWh = 22 kWh/week
• Costs: 22 kWh × 0.35 €/kWh = 7.70 €/week

Total electricity consumption per week:

• €12.25 + €7.70 = approx. €20

Per month (4 weeks):

• €80 for electricity

Total monthly costs:

Type of cost	Per month
Wood	30-40 €
Electricity (electric heating)	80 €
IN TOTAL	110-120 €

Per bathing session:

• 8 sessions/month (2x per week)
• 110 € ÷ 8 = approx. 14 € per bath

The comparison: What does the alternative cost?

So that you can assess whether that's a lot or a little:

Wood stove only (no electric):

• They must be heated from 5-10°C to 38°C before each bath.
• Duration: 3-4 hours each time
• Wood consumption: approx. 25-30 kg per session
• Cost: approx. €8-10 per bath
• Per month: approx. €65-80 (wood only)

Sounds cheaper? Wait a minute:

• They have no antifreeze (risk of damage)
• Each session takes 3-4 hours to warm up (not 30 minutes).
• You can't take a spontaneous bath.

Electric heating only (no wood):

• Heating is hardly possible in winter.
• They sit in lukewarm water and are freezing.
• Not practical.

Thermal baths/spas for comparison:

• Admission: approx. €15-25 per person
• For 2 people: €30-50 per visit
• Per month (8 visits): €240-400

The hybrid system costs you €110-120 per month and you have a hot tub at home, available at any time, privately.

The 5 biggest advantages of the hybrid strategy

Let me summarize why this setup is so clever:

1. Save time

• Using wood only: 3-4 hours heating time each time
• With hybrid: 30-45 minutes of reheating is sufficient (because the electric element kept it warm)
• You gain: 2-3 hours of free time per weekend

2. Save wood

• Using only wood: 25-30 kg per session
• With hybrid system: 15-20 kg during main heating + 5-8 kg during reheating
• You save: approx. 30-40% on wood over the winter

3. Frost protection included

• Electric heating operates 24/7 in the background
• No risk of frozen pipes, cracked wood, or defective pumps.
• They sleep peacefully , even if they are on vacation for two weeks.

4. Flexibility

• Fancy a spontaneous swim? The water is already at 30-35°C (thanks to electricity).
• Too lazy to chop wood? Electricity alone is sufficient in summer/during the transitional seasons.
• They are not dependent on a system

5. Optimal cost-benefit balance

• €110-120/month for 8+ bathing sessions
• Less than one visit to a thermal spa per person
• Your own wellness retreat , available anytime

Frequently asked questions about the hybrid strategy

Q: "Can I turn off the electric heating if I'm only heating with wood?"

A: Yes, you can. But why should you? Saving a few euros on electricity overnight (approx. €3-4) will cost you an extra 10-15 kg of wood for heating the next day (€3-5 in wood costs). In the end, you don't save anything, but you do lose time.

My recommendation: Leave the electric heater running overnight (with the lid on!). You'll recoup the costs through reduced wood consumption.

Q: "What if I'm on vacation for 3-4 weeks?"

A: Perfect use case for electric heating:

1. Set the thermostat to 8-10°C
2. Lid
3. Depart

The heating system provides frost protection for approximately €2-3 per day. You return, everything is intact, a quick heat-up with wood, and you're done.

Without electric heating you would have to:

• Empty the tub completely (work + water costs when refilling)
• Or ask someone to regularly add wood to the pile (unrealistic).

Q: "Is a more powerful electric heater (6 kW instead of 3 kW) worth it?"

A: In winter: Hardly any difference when bathing (evaporation remains the killer). But when heating with the lid closed, the time is halved (4 hours instead of 8 hours).

In summer: Definitely better if you only want to heat with electricity.

Important: 6 kW = 26 amps. Requires its own power line and fuse. Check your electrical installation beforehand (or have it checked).

My opinion: If you're already heating with wood (hybrid system), 3 kW is perfectly sufficient. If you also want to use the electric heating on its own sometimes (summer), 6 kW is better.

Q: "Can I retrofit electric heating if I currently only have a wood-burning stove?"

A: Yes, for most hot tubs. You need:

• Electrical connection (230V or 400V, depending on the heater)
• Possibly a pump (if not already present)
• thermostat

Many manufacturers offer retrofit kits. I'd be happy to advise you on whether your model is compatible.

Conclusion: The hybrid strategy is the gold standard

Here's the truth: Neither wood alone nor electricity alone is optimal in winter.

• Using only wood: It works, but you waste time and wood constantly reheating it.
• Electric only: Does not work (too weak to heat up in winter).

But together? Together they are unbeatable.

The wood-burning stove provides the power and the experience. The electric heater provides the efficiency and safety.

It's like a good team of craftsmen:

• One person does the heavy lifting (quickly, powerfully).
• The other one does the fine work (precise, reliable)
• Together they accomplish twice as much in half the time.

And that's precisely why over 80% of our customers in Baden-Württemberg and Bavaria use this setup.

It works. It saves time. It saves stress. And it costs you less than you think.

The 5 most frequently asked questions about electric heating – answered honestly

You now understand the physics, have seen the numbers, and learned about the hybrid strategy. But I know my clients – and I know what questions are still swirling around in your head.

Here are the five questions I get asked most often each year between November and March. With honest, unvarnished answers.

Question 1: "Can I use the electric heater completely on my own in the summer?"

Short answer: Yes, absolutely. And really well, in fact.

The details:

In summer (April to September) the 3kW electric heater is a perfectly adequate solution – without a wood stove .

Why this works:

At outside temperatures of 15-25°C, heat loss is dramatically lower than in winter:

• Evaporation: only approx. 0.5-1 kW (instead of 2.5-4 kW)
• Transmission: only approx. 0.2 kW (small temperature difference)
• Total loss: approx. 0.7-1.2 kW

With 3 kW heating output, you have a net output of 1.8-2.3 kW for heating.

What this means:

From cold water (15°C) to bathing temperature (38°C):

• Temperature increase: 23 degrees
• Energy required: 23 × 1.86 kWh = approx. 43 kWh
• At 2 kW net power: approx. 20-22 hours (with lid!)

In practical terms, this means:

• Friday, 6 p.m.: Heater on, lid on
• Saturday, 4 p.m.: Water temperature is 38°C, ready for swimming

My recommendation for the summer:

1. Keep the water temperature constant at 30-32°C (thermostat).
2. Cost: approx. €20-30/month (depending on usage)
3. If you want to take a bath: Briefly heat the water to 38°C (for 3-4 hours)
4. No chopping wood, no smoke, no hassle

Here's what our customers from the Stuttgart area are saying:

"From May to September, I only use the electric heater. I turn it on on Tuesdays, and by Friday after work, the tub is perfect. No hauling wood, no ash. Just get in and enjoy." – Michael K., master painter from Ludwigsburg

Costs during continuous summer operation:

• Maintaining a constant water temperature of 32°C: approx. 3-5 kWh/day
• Per month: approx. 90-150 kWh = €30-50
• Much cheaper than wood (no transport, no storage, no effort)

Question 2: "Is a 6kW heater worth it instead of a 3kW one?"

Short answer: It depends. Hardly any difference in winter, a game-changer in summer.

The details:

In winter (lid open while bathing):

Remember evaporation? That consumes 2.5-4 kW. So a 6 kW heater would:

• Supply: +6 kW
• Loss: -3.2 kW (evaporation + transmission + convection)
• Net: +2.8 kW (instead of -0.2 kW at 3 kW)

Result: The water no longer cools down during bathing, but even warms up slightly (approx. +1.5°C per hour).

That's better, but:

• They usually bathe for 1-2 hours (1.5-3°C increase = nice to have, but not essential)
• The wood stove heats you up to 38°C anyway.
• For winter bathing, 6 kW offers increased comfort, but no real added value.

In winter (lid closed, heating):

This is where it gets interesting. With the lid closed (loss only 0.5 kW):

• 3 kW heating: Net 2.5 kW = approx. 1.3°C/hour
• 6 kW heating: Net 5.5 kW = approx. 3°C/hour

That means:

• From 20°C to 38°C (18 degrees):
  • With 3 kW: approx. 14 hours
  • With 6 kW: approx. 6 hours

More than twice as fast!

In summer (sole operation):

Here, the 6kW heater is a real advantage :

• From 15°C to 38°C:
  • With 3 kW: 20-22 hours
  • With 6 kW: 10-12 hours

That means:

• Turn it on in the morning → Take a bath in the evening (instead of waiting a day)
• Spontaneous sessions possible
• Less planning required

But: The catches with 6 kW

1. Power connection:

   • 6 kW = 26 amps (at 230V) or 9 amps (at 400V three-phase current)
   • Requires its own, secure line
   • Not easily feasible in every garden
   • Installation costs: approx. €300-800 (depending on distance to the distribution box)

2. Acquisition costs:

   • 6kW heater: approx. €800-1,200 (unit)
   • 3kW heater: approx. €400-600 (unit)
   • Difference: €400-600

3. Electricity costs:

   • Double the power = double the consumption (during heating)
   • But: Heats up faster = overall similar total costs
   • Bottom line: Hardly more expensive if used correctly.

My recommendation:

6 kW is worthwhile if:

• ✅ Use the hot tub often in summer (electric only)
• ✅ You want to take a spontaneous bath (not plan it 24 hours in advance)
• ✅ The electrical installation is in place (400V three-phase power in the garden)
• ✅ You are willing to invest €400-600 more

3 kW is perfectly sufficient if:

• ✅ They primarily use the hybrid strategy (wood + electric)
• ✅ Frost protection and temperature retention are your main goals.
• ✅ You can live with 20 hours' notice in the summer
• ✅ You want to save costs

3 kW is sufficient for 80% of customers. For power users, 6 kW is a worthwhile upgrade.

Question 3: "How much electricity does continuous operation actually cost?"

Short answer: Between €50 and €120 per month, depending on usage and outside temperature.

The details (with specific scenarios):

Scenario A: Winter antifreeze (December-February, not used)

They are on winter vacation; the tub will be unused for three weeks. Thermostat set to 10°C.

Outside temperature: Average 0°C (nights -5°C, days +3°C)

Daily electricity consumption:

• Heating runs for approximately 6-8 hours/day (thermostat switches on/off)
• 7 hours × 3 kW = 21 kWh/day

Cost:

• 21 kWh × 0.35 €/kWh = 7.35 €/day
• Per month: approx. €220

But be aware: This is continuous frost (0°C average). In milder winters (5-10°C average), consumption drops drastically.

• At 5°C outside temperature: approx. 4-5 hours of operation/day = 12-15 kWh/day = €4-5/day = €120-150/month

Scenario B: Winter hybrid operation (2 baths/week + frost protection in between)

This is the setup from Block 3:

• Friday/Saturday: Keep water at 35°C (after wood stove)
• Sunday-Thursday: Frost protection at 10°C

Power consumption:

• Maintaining a temperature of 35°C for 2 days: approx. 12 kWh/day × 2 = 24 kWh
• 5 days of frost protection (10°C): approx. 7 kWh/day × 5 = 35 kWh
• Per week: 59 kWh
• Per month: approx. 240 kWh

Cost:

• 240 kWh × €0.35/kWh = €84/month

Scenario C: Continuous summer operation (May-September, constant 32°C)

They keep the water at 32°C all summer, bathing 3-4 times a week.

Outside temperature: average 20°C

Daily electricity consumption:

• Loss at 32°C water / 20°C outside: approx. 0.3-0.5 kW
• The heating runs for approximately 2-4 hours per day.
• 3 hours × 3 kW = 9 kWh/day

Cost:

• 9 kWh × 0.35 €/kWh = 3.15 €/day
• Per month: approx. €95

The overview table:

Usage scenario	Electricity/day	Cost per day	Cost per month
Winter frost protection (0°C outside, not used)	21 kWh	€7.35	€220
Winter frost protection (5°C outside, not used)	12 kWh	€4.20	125 €
Winter hybrid (2 baths/week + frost)	8-9 kWh	€2.80-3.15	85-95 €
Continuous summer operation (maintain 32°C)	9 kWh	€3.15	95 €
Summer - Occasionally (only heat up before bathing)	3-4 kWh	1.05-1.40 €	30-40 €

My recommendation to reduce costs:

1. Use a thermostat with a timer.

   • Heat only at night (nighttime electricity is often cheaper, approx. €0.22-0.28/kWh)
   • Savings: up to 30%

2. Lower the target temperature if you are not taking a bath.

   • Instead of 35°C, the temperature dropped to 25°C between swimming days.
   • Savings: approx. €20-30/month

3. Invest in a top-quality thermal lid

   • Good insulation (6-8 cm foam) reduces loss by 90%.
   • Cost: €300-500, pays for itself in 6-12 months

4. In summer: Use solar cover during the day

   • The sun provides free heating (3-5°C gain on sunny days)
   • Electricity has to work less.

Question 4: "Can I install the electric heater retroactively?"

Short answer: Yes, for most hot tubs. But there are a few requirements.

The details:

What you need:

1. Electrical connection in the garden

   • 230V (16A fuse) for 3kW heater
   • Or 400V three-phase current (16A) for a 6kW heater
   • Important: The connection must be weatherproof, grounded and protected by a residual current device (RCD).
   • Costs, if not already available: €400-1,200 (depending on distance to the house)

2. A circulation pump

   • The heating system needs water movement (otherwise it will only heat a small area).
   • Many hot tubs already have massage pumps → can be used
   • If not: A small circulation pump costs approximately €150-300.

3. Connections on the hot tub

   • Two openings (inlet + outlet) for the heater/pump
   • For wooden hot tubs: Usually present (even if not in use)
   • If necessary: ​​Drilling can be done later.

The retrofit process:

Option 1: Complete set from the manufacturer

• Many manufacturers offer retrofit kits.
• Included: heater, pump, thermostat, connections
• Cost: €800-1,500 (depending on the service)
• Installation: 2-4 hours (can be done yourself if you are handy)

Option 2: Individual components

• Heating: €400-1,200
• Pump (if needed): €150-300
• Thermostat: €50-150
• Hoses, fittings: €100-200
• Total: €700-1,850

What you can do yourself (as a tradesperson):

✅ Connect the heater and pump (mechanically)

• Install hoses, check seals
• Install pump
• Install thermostat

❌ Electrical installation in the garden (requires a professional)

• Supply line from the house to the tub
• Residual current circuit breaker, grounding
• For safety reasons: Hire an electrician.

⚠️ Commissioning

• Bleed the system (air in pump/heater = defect)
• Leakage test
• Test run

Total time required: 1 day (with electrician), of which approx. 4 hours are self-performed.

My recommendation:

If you have a hot tub with only a wood-burning stove and now want to retrofit it with electric heating:

1. Check if your model is compatible (are there ports?)
2. Get a quote from the manufacturer (a complete set is often cheaper than individual parts).
3. Have the electrical work done by a professional (safety first).
4. Install the heating/pump yourself (saves €300-500 in installation costs)

I'd be happy to advise you free of charge on whether your tub can be retrofitted. Simply call or send photos by email.

Question 5: "Does the electric heater completely replace the wood stove?"

Short answer: Yes in summer, no in winter.

The long, honest answer:

In summer (April-September):

Yes, electric heating can completely replace a wood-burning stove:

• Heating takes 10-20 hours (with lid, from cold)
• Maintaining a constant temperature costs €30-50 per month.
• No smoke, no ash, no hauling wood
• Perfect for relaxed summer evenings

Many of our customers use the wood-burning stove from October to March, and the electric heating from April to September. Best of both worlds.

In winter (October-March):

No, electric heating cannot replace a wood-burning stove.

Why not:

• Heating from cold (10°C) to warm (38°C) takes 15-20 hours.
• You lose heat while bathing (lid open) despite the heating.
• They sit in lukewarm water, shiver, and pay for electricity.

But: Electric heating is the perfect co-pilot for the wood stove:

• Wood stove heats up (quickly, powerfully, with great experience)
• Electric heating keeps the heat warm (overnight, over days)
• In short: Minimal effort, maximum comfort

The emotional component (which is often forgotten):

The wood-burning stove is not just a heater. It's part of the experience .

• The fire crackles
• The smoke rises
• They smell the wood
• You feel the heat directly from the flame.

This is wellness. This is nature. This is why you bought the hot tub.

Electric heating can do many things – but it can't do that .

What our customers say:

"In summer I only use electric heating – simple, clean, convenient. But in winter? I want to see the fire, smell the wood, the flames in the stove. It's simply part of the experience." – Thomas B., master carpenter from Ravensburg

My recommendation:

If you are considering whether you need a wood-burning stove or electric heating:

Buy both.

That sounds like more money, but do the math:

• Wood-burning stoves only: They take 3-4 hours to heat up each time, waste wood, and have no frost protection.
• Electric only (winter): Does not work satisfactorily
• Both (hybrid): Best user experience, lowest cost per session, maximum flexibility

You will recoup the €800-1,500 additional cost for electric heating through:

• Reduced wood consumption (30-40% savings)
• Less time spent (10+ hours saved per month)
• No frost damage (repair costs €500-2,000)

Amortization: 12-18 months. After that, you save money.

Summary of FAQ section

Here's what you should remember:

✅ Summer stand-alone operation: Electric heating works perfectly (20 hours preheating)

✅ 6 kW vs. 3 kW: 6 kW is worthwhile for power users and summer enthusiasts, 3 kW is sufficient for hybrids

✅ Electricity costs: €85-120/month in winter (hybrid), €30-50/month in summer

✅ Retrofitting: Possible with most models, electrician required for electrical connection

✅ Replacing a wood stove: Yes in summer, no in winter – but a perfect co-pilot

Electric heating isn't a jack-of-all-trades. But for what it was designed for, it does its job perfectly.

Conclusion: The 3kW electric heater can do a lot – if you know what

We've come a long way. From the frustrating scene on Friday evening (28°C instead of 38°C) to the hybrid strategy that actually works.

Let me summarize what you now know – and what most hot tub owners don't know:

What you now understand (and others don't)

1. Physics doesn't lie

A 3kW electric heater is not "too weak". In winter, it's fighting against an overwhelmingly powerful opponent:

• Evaporation consumes 2.5-4 kW (with the lid open)
• The heating system delivers 3 kW
• Simple math: She cannot win

But with the lid closed, the game changes:

• Loss drops to 0.5 kW
• The heater delivers 3 kW
• Net: +2.5 kW = The water heats up

The lid is not optional. It is the difference between success and failure.

2. Electric heating is not a power plant – it is a specialist.

It is built for three jobs – and it does them perfectly:

✅ Frost protection (main task)

• Reliably keeps water above 0°C
• Protects against expensive frost damage (€500-2,000)
• Costs €2-7 per day depending on the cold

✅ Maintain temperature (after the wood stove)

• 38°C on Saturday → 34-36°C on Sunday (with lid)
• Saves 70% wood when reheating
• Saves 2-3 hours per weekend

✅ Summer sole operation (April-September)

• Heats up on its own (requires 10-20 hours preheating)
• Costs €30-50/month
• No smoke, no ash, no work

What it CAN'T do: ❌ Heat from cold to hot in winter (too weak) ❌ Maintain temperature while bathing (evaporation is stronger) ❌ Replace the fire experience (that's emotional, not rational)

3. The hybrid strategy is the gold standard

Over 80% of our customers in Baden-Württemberg and Bavaria use this setup:

Winter:

• Wood stove heats up (2-3 hours, 38°C reached)
• Electric heating keeps the heat warm (overnight, over days)
• Result: Minimal effort, maximum comfort, €110-120/month

Summer:

• Electric heating takes over completely
• The wood stove remains off.
• Result: Clean, comfortable, €30-50/month

This is not a compromise. This is synergy.

The three possible paths for you

Now you've reached a point. You have the facts. You know the numbers. You understand the physics.

Which of these three types are you?

Type 1: The Purist – "I only want wood, the real experience"

This is right for you if:

• They love the fire, the smoke, the ritual
• You have time (3-4 hours warm-up per session)
• They don't bathe, or only rarely, in the summer.
• You can get wood cheaply (your own forest or contacts)

My recommendation: Stick with the wood stove alone. However: Get a small frost protection heater (500W is sufficient) for the winter if the tub isn't going to be used for 2-3 weeks. It costs €150-300 and prevents expensive frost damage.

For you, the 3kW electric heater is: Nice to have, but not necessary.

Type 2: The Pragmatist – "I want both, but cleverly combined"

This is right for you if:

• They bathe 2-4 times per month (winter as well as summer)
• You want to save time (not have to heat it up for 3 hours every time)
• They appreciate flexibility (wood in winter, electricity in summer)
• They are prepared to invest €1,000-1,500 in a complete set.

My recommendation: A hybrid system from Block 3. Wood stove for power, electric heating for efficiency. This is the setup I use myself – and which I recommend to 8 out of 10 customers.

Total costs: €110-120/month (winter), €30-50/month (summer). Amortization: 12-18 months (through wood savings + time savings).

For you, the 3kW electric heater is a must-have. It doubles your comfort.

Type 3: The summer enthusiast – "I want things uncomplicated, mainly in summer"

This is right for you if:

• They primarily bathe from April to September.
• They don't want to haul/store wood
• If you want to decide spontaneously (no planning 3 days in advance)
• They only bathe occasionally in winter (then with wood)

My recommendation: Opt for a 6kW electric heater (not 3kW!). This halves the heating time in summer (10-12 hours instead of 20), and you can decide in the evening: "I want to take a bath tomorrow evening."

Total cost: €40-60/month (continuous operation in summer at 32°C) Advantages: No smoke (neighbors will be happy), no work, always ready

For you, electric heating is the primary heating system. 6 kW is your sweet spot.

Still unsure? Here's my offer to you.

I know: €1,500-€5,000 for a hot tub (or a retrofit kit) is an investment. And you want to be sure you're buying the right one.

Therefore, I offer you the following:

➡️ Book a free hot tub consultation

💬 What our customers say:

"For two years I only had the wood-burning stove. Three hours of heating every weekend, and the tub sat cold during the week. Since I retrofitted the electric heating, everything is different: a quick wood fire on Friday, and it's still warm on Saturday and Sunday. And in the summer I only use the electric heater. Best investment ever." – Michael K., master painter from Ludwigsburg

"Jens told me honestly: 'For your usage (only in summer, 1-2 times a month), a 6kW electric heater is sufficient; you don't need a wood-burning stove.' He could have sold me the expensive hybrid model. But he gave me honest advice – and I'm grateful for that. Since then, I've recommended him to everyone." – Sabine T., dentist from Ravensburg

"The physics explanation in this article was a real eye-opener. I always thought my heating system was broken. But no – it's doing exactly what it's designed to do: frost protection and maintaining the temperature. Now I'm using it properly, and it works perfectly." – Thomas B., master carpenter from Freiburg