Thermalec Electric heaters have been used for many varied applications including Underfloor Heating, Canine & Equine Hydrotherapy Pools, Baptist Pools, Cheese Vats, Fountains, Fish Ponds and even a Shark Tank in Brighton Aquarium.
heated swimming pool thermalec
We also design heaters to specialist requirements for use on luxury yachts and cruise liners, central heating systems and greenhouses.
Future projects include under-floor heating, food processing, bio-fuel applications.
Thermalec export most of the water heaters around the world for swimming pools, spas and specialist applications.

12PHR Swimming Pool Heater

thermalec 12THR swimming pool heater
Cast in BS-EN-1561-1997-ENGJL-200 iron, with a heavy fusion bonded epoxy coating impervious to chemically treated pool water, constructed in accordance with British Patent 2.092,282 Design pressure of 35psi (2.46kg/cm2) with 3/4″ safety valve(s) set to operate at the maximum normal working pressure of 30psi (2.1kg/cm2) giving protection to both the heater and the installation as a whole against over pressure. A 1/2″ drain valve at the lowest point allows the heater to be left empty in winter. Flow connections consist of easily removable uPVC stub flanges into which the pipes may be fitted using suitable adhesive, as the flanges can be released easily from the heater no unions are required, nor is any form of heat sink needed. Flow direction is from left to right, but may be reversed quite simply on site following the installation instructions.
The construction of the heater is solid and robust, to ensure years of safe and reliable service.
The contact materials are highly resistant to corrosion from pool chemicals. Thermalec® pool and spa heaters can safely be used with sea water pools as well as in demanding applications such as Hydro- and Thalasso- therapy.
The watts density of the heating elements is very low (9.54 W/cm²), ensuring minimal scale build-up and long element life.
The heating elements are always submerged in water. Any air bubbles entering the heater pass through it above the water and across the unheated parts of the elements, preventing any damage to the latter.
The patented weir and baffle system inside the heater causes the water to flow through it in a spiral. This increases uniformity of the water temperature inside the heater and prevents direct impingement of cold water onto the elements.
The spiral flow regime of the water inside the heater discourages scale formation, extending element life.
The heaters have no flow switch. These are notoriously unreliable. Any air bubbles passing through the heater will cause any flow switch to make and break repeatedly in rapid succession, causing the contactors to do the same, thus shortening their life.
Thermalec® heaters are flexible: The water flow direction is normally left to right. If required, this can be easily changed on installation by means of a simple modification. Most models may be easily changed by a qualified electrician from single to three phase operation and vice-versa.
The thermostats used in Thermalec® pool and spa heaters have a low operating differential. This is essential to maintain the swimming pool at a virtually constant temperature.
Heaters with higher operating differentials are likely to allow the pool to cool to an uncomfortably low temperature before switching the heating on.
Top quality contactors have been used and their ratings generously selected to give a long service life and minimum risk of operational problems, particularly in pool plant room
As a safety precaution, the heaters are provided with an interlock relay, which has to be connected to the filter pump control circuit. The heater will not operate unless the interlock is wired and the filter pump is energised.
Status indicator lamps on front of panel to facilitate troubleshooting and diagnostics.
Thermalec® pool and spa heaters comply with all current and relevant EU regulations and directives.
Thermalec® pool and spa heaters have a two-year guarantee.
Protection level: IP 21
Fuses: 1 x 2 Amp (+1 spare)
Pump interlock voltage: 230 V AC
Element heat flux: 11.5 W/cm² max.
Packed dimensions: 425 x 450 x 190mm
Packed weight: 26 kg
thermalec swimming pool and spa heaters

Zenith Range of Pool Heaters

Expanded range: 8, 16, 24, 48, 72, 96, 120, 144 & 168kW
Uses electronic time delay relays
Simplified design
Simple & highly effective heat transfer into the water
Larger sizes allows an installation reduction in pumps, piping, valves and control gear
Reduce overall cost of projects
swimming pool water fountain thermalec
Unique spiral flow allows efficient heat removal from the elements, minimising the scale and sediment build up.
Unique design ensures cooler water from filter pump does not strike the elements direct (giving longer life).
Air generated from the pump passes harmlessly around the sides of the baffles and across the top of the heater elements (heat pumps heat both air and water).
The control thermostat is positioned to sense the incoming water temperature and controls the pool to within 1°c.
The safety thermostat senses the water temperature leaving the heater.
Thermalec® Heaters can be used in conjunction with other heating systems to provide year round heating solutions for your pool or spa.
Each heater is designed with its own simple self diagnostic system.
Heating Elements always submerged
Safety Thermostat
The ZENITH range of heaters is in keeping with the intrinsic values of Thermalec® heaters, with its robust cast iron water vessel housing the new Titanium or Incoloy 825 8kW heating elements. ZENITH is designed with Thermalec’s unique spiral flow to allow the pool or spa water to flow through the heater to reduce scale build up.
The new control system features a 3 or 4 stage (depending on heater size) power-up sequence using electronic time delay relays to avoid power drain on full start-up. Each electronic time delay relay is variable, allowing the sequence of start-up to be varied to the requirement of the installation. This is a very useful facility, as in certain installations such as a pool or spa on a ship or yacht variable time delays are invaluable.


Five whole months of swimming in beautiful clear clean water at temperatures well above those of the Mediterranean with a heating cost that is less than the cost of one package holiday for a week.
With a 12’ by 24’ pool the total running cost of both heater and filter pump can be less than £ 430 for 22 weeks swimming at 80ºF as shown in the example given below.
Using a Thermalec heater and taking advantage of low cost electricity at night for both heating and filtration gives you up to 22 weeks of summer swimming, without ever leaving your own garden.
Taking a pool with a solar cover maintained at 80ºF for the whole 22 week season from early May to the end of September, our experience over 40 years is that you can expect on average a heat loss equal to 28 Units of electricity per sq.ft. or 300 Units per M² of pool surface area.
This will be the heat loss from a pool of this size held at this temperature regardless of the type of heating system used. This then gives you a yardstick by which we may compare running costs.
To find out the seasonal consumption, simply multiply the sq.ft. of surface area by 28 (or M² by 300).
Most people we talk to do not realise that a pool only alters in temperature 2 or 3 degrees in 24 hours, but being a large mass of water it is thermally very stable. Consequently, heating a pool by night is the perfect way of using Economy 7 which is now much less than half-price electricity – much nearer 1/3rd of the daytime rate.
The Thermalec utilises this power in the most economical way possible. Unlike a storage heater, which heats its core up to a very high temperature, much of which heat must be given off during the following day – The Thermalec simply heats its storage medium, the water you swim in, to the exact temperature you want to swim in and not one degree more.
Heater Operation diagram
1. Heating Elements (always fully submerged) 2. Air passes safely above the elements)
3. Curved base (swept clean of scale and sediment)
For example a 12 x 24 ft pool has a surface area of 288 sq.ft, multiply this by 28, you have 8064 Units. If the price you pay for E7 electricity in your area is 4.92 pence per unit, then the total cost per season is £ 0.0492p x 8064 Units =39675 pence or in other words, roughly £ 397.00 per year.
One of the many benefits of using a Thermalec on Economy 7 is that a dramatic reduction is made on the cost of filtration, as, in private pools, it is normally arranged for the filter pump to run during the E7 period. A ¾HP pump uses 0.55 units per hour or 4 units in 7 hours, which at £ 0.0492p per unit, costs £ 0.20p per night or £ 31.50 per season. The heating and filtration costs together come to just £ 428.50 using the Thermalec system.
With other systems the filtration costs add considerably to the total running costs. If for instance you compare this with a Heat Pump of the same daily output as a Thermalec, it can only give this output if the filter pump runs 24 hours per day and that will be on day-rate electricity at approx. £ 0.179p a unit.
The heating cost is still based on replacing the 8064 units heat loss from the pool. Whilst the heat pump takes 3 parts from the air and one part from the mains, the 2000 units of electricity it does consume are at the day-time rate of £ 0.17.9p making a heating cost of only £ 358.00
But the cost of running the same filter pump as above for 24 hours, just to transfer the heat from the Heat Pump to the pool is then 0.55 units x 24 hours x 7 days x 22 weeks x £ 0.179p per unit which comes to £ 285 for the season on filtration alone and with the £ 280 heating cost totals £ 720.