A hot tub spec sheet looks like a list of facts, but it is really a marketing document with technical numbers in it. Some figures are hard data (volume, dimensions, heater output), others can be inflated almost at will (jet count, pump power in HP) — and the single most important one, the type of insulation, often does not appear in the catalogue at all. This article walks you through it line by line and shows you where to stop and ask.
We assume you already have a rough idea of the kind of hot tub you are looking for. If not, start with the general guide on how to choose a hot tub and the comparison of a small versus large hot tub. This article is about something else: the ability to put two catalogue sheets side by side and tell which manufacturer actually stands behind what it prints.
Dimensions and weight: two weights, not one
Dimensions are usually given as length × width × height in centimetres. Be aware that the height is normally measured without the cover and without the levelling feet, and that the cabinet may overhang around the perimeter for handrails or steps. When planning your space, add at least 50–60 cm on one side of the footprint for service access to the equipment — without it, a service engineer cannot reach the pump unless the whole tub is dragged out of position.
The most common trap is weight. Catalogues like to quote the dry weight (empty shell, typically 250–450 kg for four- to six-seat models). What determines the load on your floor, however, is the filled weight — the tub plus the water plus the people. A hot tub holding 1,200 litres with four people in it comes to roughly 250 + 1,200 + 320 = around 1,800 kg spread over a few square metres. That is an entirely different order of magnitude from the dry weight, and it is precisely the figure you need for a deck or a balcony — the article on a hot tub on a terrace and structural load covers it in detail.
Water volume: the number that drives both heating and chemistry
Volume is given in litres and tends to be more honest than other entries, because it can easily be verified with a water meter. Typical ranges: two-seat hot tub 600–900 l, four-seat 900–1,400 l, six- to eight-seat 1,400–2,000 l, swim spas 4,000 l and up.
Volume matters on two levels. First, heat-up speed: raising 1,000 litres by 1 °C takes roughly 1.16 kWh of energy, so with a standard 3 kW heater you will warm a thousand-litre tub by about 2.5 °C per hour (before losses; in practice, less). Heating from 15 to 38 °C therefore takes ten to fifteen hours — we go through the figures and the options in the article on how to heat a hot tub and pool faster.
Second, chemistry: dosing is calculated per cubic metre of water, and a smaller volume forgives fewer mistakes. In 700 litres an overdose shows up immediately; in 2,000 litres you have more margin. At the same time, a smaller volume loads up with organic matter faster for the same number of bathers.
Seat count: paper capacity versus real capacity
The seat count is the sum of every seat and lounger listed in the catalogue, not the number of people who will feel comfortable in the tub. The difference is usually one to two people. A six-seat hot tub measuring 200 × 200 cm is comfortable for four adults; six will fit only if everyone knows each other very well.
So watch three other figures instead: how many loungers there are (a lounger takes up the space of two seats), whether the tub has a deep seat for taller people, and what the internal width in the corners is. The corner seat is usually the most comfortable spot in the tub — and there is usually only one of them.
Jet count: the most inflated number on the whole sheet
“Sixty-five jets” sounds impressive but says nothing about the strength of the massage. The count routinely includes small rotary jets 2–3 cm in diameter, air injection ports and footwell jets. What actually matters is something else: how much water the pump delivers and how it is divided up. The same pump split between 20 jets gives a powerful massage; split between 50 jets it gives a weak, fizzy sensation.
On the spec sheet, therefore, look for the ratio of jets to pumps and for information on whether the jets are split into zones with a diverter. A hot tub in which every jet runs at once off a single pump has less power available for each one. You will find an overview of jet types and what they do in the article on hydromassage jets and their types.
Pumps: HP, kW and why the numbers do not add up
This is where it gets most confusing. Power is quoted both in horsepower (HP) and in kilowatts, and the relationship between the two is ambiguous, because two different metrics are in circulation:
- BHP / brake horsepower — power at the shaft, a real figure.
- SPL / “spa pump label” HP — an inflated value that factors in the service factor. A pump badged 3.0 HP may have a real continuous output equivalent to 1.5 BHP.
A more reliable guide is therefore the electrical input in kW or the current draw in amps. The massage pump in an ordinary family hot tub draws roughly 1.5–2.5 kW; a circulation pump for filtration only 0.15–0.25 kW. If the sheet shows only HP and no watts, you are missing the information you need to calculate running costs.
Watch the type as well: a two-speed pump can run at low speed for filtration and at high speed for the massage, so it replaces a separate circulation pump — but the filtration cycle then uses more energy than a quiet dedicated circ pump would. A model with a separate circulation pump is usually cheaper to run and quieter in service.
Heater and electrical supply: one dictates the other
In the vast majority of domestic hot tubs the flow-through heater element has an input of 3 kW. Higher figures (6 kW) appear on swim spas and on models built for cold climates. A higher input means faster heating, but also greater demands on the circuit protection.
Connections fall into two categories. 230 V / 16 A (plug & play) means the whole hot tub has roughly 3.5 kW available — and that is the ceiling for the heater and the pumps combined. The control unit therefore shuts the heater off when the massage is switched on, so the water cools during a long soak. 400 V / 3 × 16 A gives you headroom: the heater runs independently of the jets and heat-up is noticeably faster. The differences, the electrical inspection and the requirements for the supply are covered in the article on hot tubs and electrical connection.
On the spec sheet, check whether the stated current draw is total or per phase, and whether the manufacturer allows for a type A residual current device with a residual current of 30 mA — that is mandatory for hot tubs.
Insulation: the most important figure and the hardest to find
The type of insulation affects running costs more than everything else put together, and yet in the catalogue it is usually described in a single sentence, or not at all. There are three basic versions:
| Type of insulation | Construction | Effect |
|---|---|---|
| Full foam (fully foamed cavity) | The entire space between the shell and the cabinet is filled with PU foam | Lowest heat losses, quiet running; pipework servicing is more laborious |
| Perimeter | Insulation on the inside of the cabinet, foam sprayed onto the shell, an air cavity inside | A compromise; uses waste heat from the pumps, good access to the equipment |
| Minimal / none | Only a thin layer on the shell, empty cabinet | Markedly higher consumption, especially in winter; typical of the cheapest models |
When the spec sheet says only “insulated cabinet” with no further detail, ask about the thickness and the material, whether the base is insulated too, and whether the cover (thermal cover) has a stated thermal resistance value. How insulation shows up in your monthly bills is set out in the article on how much a hot tub costs to run.
Control unit: think ahead to servicing
The make of the control unit determines the availability of spare parts for the next ten years. The most widespread are Balboa and Gecko; you will also come across In.Ye, Chinese SpaNet and proprietary systems. For the widespread platforms you can source the board, the flow switch and the heater element from several suppliers, and the engineer knows the error codes by heart — our overview of Balboa error codes will help you find your way around.
With a proprietary system you are dependent on a single importer. If they drop the brand, a repair five years down the line may make no economic sense. On the spec sheet, therefore, look for a specific board type designation, not just “digital control with a touch panel”.
Filtration, ozone and UV
For filtration, the sheet gives the type (cartridge, or on more expensive models a skimmer chamber with several cartridges) and the filter area in square feet. A larger area means a longer interval between cleanings and lower pressure loss. For a four-seat hot tub, a sensible minimum is around 50 sq ft; 25 sq ft means cleaning every ten days. The procedure and the intervals are described in the article on cleaning a hot tub filter.
An ozonator is fitted even to cheaper models; a UV lamp tends to belong to the higher class. Both reduce chemical consumption, but neither replaces disinfection — something the spec sheet almost never mentions. How the two technologies differ and what they can genuinely do is examined in the article on UV lamps and ozone in disinfection.
Running costs: a number without test conditions is worthless
The figure “1.8 kWh/day” carries no meaning on its own. Ask what conditions produced it: at what ambient temperature (the usual test runs at 20 °C ambient, which corresponds to June, not January), at what water temperature, with what cover and on what filtration schedule. The same hot tub can use 2 kWh/day in summer and 8–10 kWh/day in freezing weather.
An honest manufacturer states consumption as a range for summer and winter, or at the very least spells out the test conditions clearly. A single number without context is marketing.
Warranty: broken down by component, not one number
A “5-year warranty” in a catalogue is almost always shorthand for several different periods. The typical breakdown: shell (acrylic) 5–10 years, cabinet structure 2–5 years, equipment (pumps, heater, control unit) 2 years, seals, bulbs and filters no warranty at all. For consumer goods, the statutory two-year liability for defects applies regardless of what the manufacturer promises on top — the article on warranty claims for pools and hot tubs sums up how to proceed.
Also check whether the warranty is conditional on installation by an authorised engineer and whether it covers travel and labour or only the spare part. The difference between “we will replace the board free of charge” and “we will send the board, you pay for the call-out” runs into the hundreds of euros.
Summary table: figure, meaning, trap
| Catalogue figure | What it means | What to watch out for |
|---|---|---|
| Dimensions (l × w × h) | Footprint and height of the shell | Add 50–60 cm for service access |
| Weight | Usually dry weight, empty shell | For structural loads, count the filled weight including people |
| Water volume (l) | Shell capacity | Determines both heat-up speed and chemical dosing |
| Seat count | Sum of the seats in the catalogue | Real capacity is usually 1–2 people lower |
| Jet count | Sum of every opening, small ones included | Means nothing without pump power and zone split |
| Pump power (HP) | May be SPL or BHP | Ask for the input in kW or the draw in A |
| Heater (kW) | Heater element input, usually 3 kW | On 230 V the heater competes with the jets |
| Connection | 230 V plug & play vs. 400 V | Check the draw per phase and whether a dedicated supply is needed |
| Insulation | Full foam / perimeter / minimal | The most frequently missing and yet costliest item |
| Control unit | Balboa, Gecko, proprietary | Decides parts and servicing 5–10 years out |
| Filtration (sq ft) | Area of the filter cartridge | Small area = frequent cleaning and higher pressure loss |
| Ozone / UV | Supplementary disinfection | Does not replace chlorine or bromine |
| Consumption (kWh/day) | An estimate from a test | Useless without the ambient and water temperature |
| Warranty | Different periods for different parts | Check whether it covers labour and travel |
Red flags in a catalogue
When you come across one of these points on a spec sheet, it does not necessarily mean fraud — but it is a signal to ask in writing, ideally by email, so that the answer carries weight.
- No information on insulation. The strongest warning sign of all. A manufacturer with full foam insulation makes a point of it; one that stays silent usually has nothing to boast about.
- Jet count only and no pump specifications. A classic on models sold by online shops with no service network.
- Consumption with no test conditions. A single number with no ambient temperature, water temperature or filtration schedule.
- Power quoted in HP alone. Without kW or amps you cannot calculate anything.
- “Digital control system” with no type. The make and model of the board are public information; if they are missing, ask why.
- Warranty as a single number. Ask for the component-by-component breakdown up front, not when you come to make a claim.
- No filled weight. For a hot tub destined for a deck this is fundamental groundwork, not a detail.
Frequently asked questions
Can you tell the quality of the acrylic from the spec sheet?
Not directly, but indirectly yes. Look for the material designation (typically sanitary acrylic with ABS or a glass-fibre-reinforced layer) and the length of the warranty on the shell. A 10-year shell warranty is a stronger indicator than any description of the material.
Are more pumps always better?
No. Two pumps make sense on hot tubs with six or more seats, where several zones need to be fed at the same time. On a four-seat tub they mainly raise the purchase price and the running costs. What matters is how many jets there are per pump.
Why do catalogues give the filter area in square feet?
Most cartridge filters derive from American standards, where the area is quoted in sq ft. The conversion is simple: 1 sq ft is roughly 0.093 m². A figure of 50 sq ft therefore corresponds to about 4.6 m² of filter area.
What does “heats 1.5 °C per hour” actually mean?
It is the result of one particular test, not a constant. It depends on the water volume, the heater input, the outdoor temperature and whether the cover was on. On the same model it can be half the quoted figure in winter.
Should I ask for a spec sheet on a used hot tub too?
Absolutely. On a second-hand tub the type of control unit and the type of insulation matter even more than on a new one, because they decide whether it is worth repairing at all.
Before you sign the order
Read a spec sheet backwards: insulation, electrical connection and control unit first, and only then the jets and the styling. The first three items decide what the hot tub will cost you over ten years; the last two decide how it looks in the photograph. If one of the key figures is missing, that is not necessarily a fault in the product — but it is a reason to ask before the invoice arrives.
You will find the full specifications, the type of insulation and the control unit used on every model in our range of hot tubs. And if you are interested in more practical reading on choosing and running one, browse the Guide section.
