Grundfos UPS vs. Grundfos solar pumps – which one suits your system

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Grundfos UPS vs. Grundfos Solar Pumps – Which One Fits Your System?

Grundfos is a name you'll find in practically every second boiler room in Slovakia. We install circulation pumps of this brand in single-family homes, apartment units, and larger buildings on a daily basis, and customers often ask us the same question: "What is the actual difference between UPS pumps and the solar ones? And which one should I buy?" The answer is not simple and depends on several factors – the type of heating or solar system, hydraulic requirements, regulation, and not least, the amount of energy you want to save. This article will help you make the right decision without unnecessary confusion.

First, we'll explain what each of these pump types actually is, how they work, where they are used, and what their real strengths and weaknesses are. Then we'll move on to a comparison and practical scenarios that will help everyone – from the owner of a single-family home with a gas boiler, through someone interested in solar thermal heating, to the installer looking for the right pump for a specific job.

What is Grundfos UPS – Principle and Typical Use

Grundfos UPS (Unipump Standard) is a classic three-speed circulation pump with a wet-rotor asynchronous motor. In practice, this means that the pump rotor (and also the bearings) is cooled directly by the pumped liquid – not by air or oil. This design is extremely robust, quiet, and requires almost no regular lubrication maintenance.

The basic principle of regulation is simple: the pump has three fixed speed levels (1, 2, 3), and the technician sets the one that corresponds to the hydraulic conditions of the system during installation. Most domestic installations run on level 2 or 3. The motor runs at constant speed, the pump delivers a constant flow and pressure – regardless of how many thermostatic valves are currently open.

Typical applications of UPS pumps include:

Heating circuits with a boiler (gas, electric, solid fuel)
Distribution systems with radiators, underfloor heating, or a combination of both
Circulation circuits for hot domestic water (HDW)
Systems with an accumulator tank
Cooling circuits in air conditioning and heat pumps (only some types)

The most classic representative of this group on the Slovak market is the GRUNDFOS UPS 25-30 – a pump with a DN25 (1 inch) connection diameter and a maximum pumping pressure of 3 m w.c. (0.3 bar). You will find this pump in single-family homes with a standard boiler and radiator system more often than any other type. It is compact, inexpensive to purchase, easy to install, and the manufacturer guarantees a long service life – typically 10 to 15 years without any service intervention.

What is Grundfos Solar – Principle and Typical Use

Grundfos Solar is a completely different category of pumps that was developed specifically for solar thermal systems – that is, roof-mounted collectors that heat water using solar energy. These pumps are designed for operation with a heat transfer fluid containing an antifreeze mixture (usually glycol-water in a 50/50 ratio), which can reach temperatures from –30 °C (stagnation in winter) to more than +130 °C (stagnation in summer, when the system is not operating).

The key difference from the standard UPS is therefore primarily the resistance to these extreme temperature conditions and the chemical compatibility with the solar fluid. Seals, rotors, and bearings are made of materials that do not swell, do not lose elasticity, and do not corrode even after years of operation with aggressive glycol. The basic UPS is not designed for this, and the installation of a standard circulation pump into a primary solar circuit is a fairly common mistake that usually results in a failure within two to three seasons.

Solar pumps from Grundfos are also manufactured with electronically adjustable speeds (EC motor), which allows flow regulation depending on the current solar performance. Alone or as part of control stations (so-called solar stations), these pumps are suitable for:

Solar collectors for the preparation of hot domestic water
Solar heating support (combination with an accumulator tank)
Larger community or commercial solar systems
Garden solar systems for pool heating

Among the available products in this category on Atria.sk, specific examples available include the GRUNDFOS Solar 25-120, 180 mm or the smaller model GRUNDFOS Solar 15-80, 130 mm. The numbers in the name speak for themselves: the first number is the DN assignment (15 = 1/2", 25 = 1"), the second number is the maximum head in tenths of a meter (120 = 12 m w.c., 80 = 8 m w.c.). The number after the comma (130 mm, 180 mm) is the shaft distance – that is, the distance between the suction and discharge nozzles, which affects compatibility with the mounting station or collector valves.

Main technical differences between UPS and Solar pumps

Now we will compare both groups in depth, because it is precisely in the technical details that the answer lies to the question of which pump is the right one for you.

Temperature resistance and medium

Standard UPS pumps are designed for operation with clean heating water (or water with corrosion inhibitor) in a temperature range typically from –10 °C to +95 °C, with continuous operating temperature not exceeding +90 °C for long periods. Most manufacturers guarantee safe operation with a liquid containing up to 30 % glycol mixture under normal conditions, but this is far from their optimal purpose.

Grundfos Solar pumps are certified for operation with a liquid containing up to 60–70 % propylene glycol mixture and can withstand temperatures above +130 °C (collector stagnation temperature in summer). Seals are made of EPDM or PTFE (teflon) instead of standard rubber, the shaft is made of stainless steel, and the rotor chamber is made of materials resistant to degradation at high temperatures. This is precisely the crucial boundary – if you install a standard UPS in a solar circuit, on the first hot summer day when the collector reaches 120–140 °C and the pump stops (power outage, regulation switching), the UPS seals may crack and the pump will start leaking.

Speed regulation and electronics

A classic UPS has three fixed levels set by a mechanical switch. It is simple, reliable and proven over decades. The drawback is that the pump always draws the same power – for example, 45 W at level 2 – regardless of whether the heating system needs full flow or most of the radiator valves are closed and we only need 20 % capacity.

Higher-grade Grundfos Solar pumps (e.g. Solar 25-120) are usually equipped with an EC (electronically commutated) motor with continuous speed regulation. The solar station controller (e.g. Grundfos CM10 or another standalone controller) can change the pump speed depending on the temperature difference between the collector and the storage tank. When the sun is strong and the collectors are hot, the pump runs at full power. When it is cloudy and the temperature difference is small, the pump slows down, minimizing pipe heat losses and maximizing energy efficiency.

Hydraulic parameters

Typical UPS pumps for family homes cover a range of discharge heads from 2 to 6 m w.c. at flows of 0.5–3.5 m³/h. For floor heating with long circuits and high hydraulic resistance, UPS 25-60 or UPS 25-80 is sufficient. For short radiator systems in a smaller house, GRUNDFOS UPS 25-30 is sufficient.

Solar pumps cover a different range – Solar 25-120 can pump up to a height of 12 m w.c. Why so much? Solar collectors are usually on the roof (height 3–8 m) and pipe runs of tens of meters have higher hydraulic resistance when working with glycol, which is thicker than pure water. A larger model is therefore not oversized – it is realistically designed for a typical solar system in a family home with 4–8 m² of collectors.

Concrete practical scenarios – what fits where

Scenario 1: Family house with gas boiler and radiators

A classic family house with an area of 120–150 m², a gas condensing boiler, 8–12 radiators with thermostatic heads. This is the territory for an UPS pump without any doubts. Specifically – GRUNDFOS UPS 25-30 for houses with lower heating output (up to about 10 kW) or UPS 25-60 for larger buildings. If the house also has floor heating in part of the space (e.g. hallway and bathroom), it is necessary to dimension according to the circuit with higher hydraulic resistance – usually this will be UPS 25-60 or UPS 25-80.

Installation is straightforward: the pump is connected to the boiler's supply or return, stage 2 or 3 is set according to the hydraulic calculation, and the system runs. More about this process can be found in the article Installation of Grundfos circulation pump step by step or in How to choose the right Grundfos circulation pump for heating.

Scenario 2: Solar system for DHW preparation for a family of four

A flat collector of 2×2 m² on a roof inclined at 35°, a 200-liter tank in the basement on the ground floor. The height from the tank to the collector is 4.5 m, the pipe length is 18 m (copper 22 mm), the medium is a 50 % propylene glycol mixture. The hydraulic resistance of such a system typically comes to 4–7 m w.c. at the required flow of 2–3 l/min per m² of collector, i.e. 6–9 l/min in total.

The ideal pump for this system is GRUNDFOS Solar 15-80, 130 mm – a smaller model with a 130 mm shaft length, which is easily mounted in a compact solar station. Do not forget that the solar station should also include a flow meter, safety valve, expansion vessel and air vent – the pump alone is not enough.

Scenario 3: Combined system – boiler + solar + heat pump

This is an increasingly common case: a modern family house with an air/water heat pump as the main source, an electric boiler as a backup, a 6 m² solar collector for DHW preparation and a floor heating system. In such a system you can have three separate pumps at the same time:

Internal pump of the heat pump (usually part of the device)
Circulation pump of the heating circuit – UPS or modern Grundfos MAGNA (EC motor)
Solar pump of the primary circuit – Grundfos Solar 25-120 or Solar 15-80

Mixing these pumps is a mistake we see in practice relatively regularly. The most common mistake: an installer mounts a standard UPS in a solar circuit, because „it is the same pump, just differently named". It is not. After the first summer with collector temperatures above 100 °C, the pump is either seized (blocked) or leaks from the shaft.

Scenario 4: Drainage and water pumping – UNILIFT pumps

Common customer mistake: sometimes they also look for rainwater pumps or basement drainage pumps in the Grundfos category. Here, submersible pumps come into play – for example, the GRUNDFOS UNILIFT KP 150 A1 or the more powerful GRUNDFOS UNILIFT KP 250 A1 with 10 m cable. These pumps have nothing in common with the circulation of heating water or solar circuits – they are pumping pumps for clean or slightly contaminated water, for example during floods, drainage, tank emptying or garden pumping. We mention them here so customers know where the boundary is and that we are now in a different product category.

Energy efficiency – UPS vs. Solar pumps

Traditional UPS pumps belong to the EEI (Energy Efficiency Index) class of 0.23 and higher – so they are not the most efficient. Modern EU regulations (ErP 2013 and 2015) have effectively pushed old asynchronous pumps for public buildings off the market and force manufacturers to use EC motors. For single-family homes, exceptions apply and UPS pumps are still legal and sold, but you should expect their power consumption of 30–70 W (depending on the model and stage), running 24 hours a day during the heating season.

Approximate calculation for a typical house: a stage 2 UPS pump has a power consumption of 45 W. The heating season lasts about 200 days. Per year: 45 W × 24 h × 200 days = 216 kWh/year. At an electricity price of 0.25 €/kWh, this is 54 €/year. For comparison, a modern EC pump (Grundfos ALPHA or MAGNA) would consume 10–20 W under the same load, thus saving 15–35 €/year. The savings are not dramatic, but over the 15-year lifespan of the pump, they add up to 225–525 €.

Solar pumps are also EC-motor based and consume 10–40 W depending on the set speed. Their operation, however, is much shorter – only during the day, only when the sun is shining and the collectors have enough temperature (typically 3–8 hours a day, 150–200 days a year). Annual consumption of a solar pump is therefore much lower than that of a heating circulation pump – in the range of 30–80 kWh/year.

Installation differences and what to know during installation

Mechanical installation of both types looks similar at first glance – both are wet-rotor pumps with threaded or flanged connections. However, there are several important differences:

Mounting direction: Both UPS and Solar pumps can be installed horizontally (motor on the side) or vertically (motor on top). The motor must never point downward – it risks flooding the bearings. UPS pumps are mounted on the supply or return line of the heating boiler, Solar pumps exclusively on the primary solar side.
Insulation housing: UPS pumps have no special thermal requirements. Solar pumps should have an insulation housing (usually part of the mounting station) to minimize heat losses in a cold boiler room.
Electrical connection: UPS pumps 1×230 V are straightforward – phase, neutral, ground. Solar pumps can be controlled by a digital controller via a 0–10 V signal or PWM. Never connect a solar pump directly to a circuit breaker without a controller – you will lose all functionality of automatic regulation.
Depressurization: Glycol foams more than clean water, so depressurization of the solar circuit is more complicated. We recommend an automatic air vent at the highest point of the system and manual depressurization after each filling.

How to correctly dimension a pump – basic rules

For heating UPS pumps, the following basic dimensioning rules apply:

Boiler power (kW) × 0.86 / ΔT (°C) = flow (m³/h): For a 15 kW boiler with a temperature difference of 10 °C, the flow is 15 × 0.86 / 10 = 1.29 m³/h
Specific pressure loss of the pipe × length of the circuit = hydraulic resistance: Copper DN18 has a specific loss of about 100–150 Pa/m at a flow of 1.3 m³/h. For a 30 m circuit (there and back), this is 3–4.5 kPa = 0.3–0.45 m w.s. + losses on valves, boiler, etc. Together, typically 2–4 m w.s. for a simple radiator system.
Select a pump so that the operating point (flow + pressure) lies in the middle third of the characteristic curve. A pump that is too large (operating point to the left) is noisy and causes cavitation, a pump that is too small (operating point to the right) cannot pressurize the system.

For solar pumps, a similar procedure applies, but with a correction for the higher viscosity of the glycol mixture – the hydraulic resistance of the system is 20–40% higher than with pure water (depending on the glycol concentration and temperature). This is another reason why the Solar 25-120 with a head of 12 m is not oversized – you actually need that performance.

If you are unsure about the calculation, we recommend the article What Grundfos pump power do I need for my house, where the procedure is explained step by step even for laymen.

Cooperation with solar control – what the controller controls

A solar pump never runs "dry" without a controller. A solar controller (differential thermostat) measures the temperature at the collector (sensor T1) and the temperature at the bottom of the storage tank (sensor T2). When the temperature difference is greater than the set value (typically 8–10 °C), the controller turns on the pump. When the difference drops below 3–4 °C (the tank is sufficiently heated or the sun is covered by clouds), the pump is turned off.

This switching on and off must be properly set – if the activation differential is too small (e.g. 3 °C), the pump will cycle up and down quickly, which is not good for the fluid or the electric motor. If it is too large (e.g. 15 °C), you lose part of the solar yield in the morning and evening.

More about the function of solar pumps can be found in the accompanying article of the knowledge center Grundfos solar pumps – what they are used for and how they work, where more advanced control functions such as overheating protection, night cooling and frost protection in winter are also described.

Comparison table UPS vs. Solar – a brief overview

Property	Grundfos UPS	Grundfos Solar
Temperature resistance	up to approx. 95 °C	up to 130 °C (stagnation)
Medium	Heating water, max. 30 % glycol	Glycol up to 60–70 %, solar fluid
Control	3 fixed levels (switch)	EC motor, delta T controller
Typical head	2–6 m w.c.	8–12 m w.c.
Power consumption	30–70 W (constant)	10–40 W (variable, controlled)
Seals	Standard rubber	EPDM / PTFE (teflon)
Shaft distance	130 mm (standard)	130 mm or 180 mm
Typical price	Lower	Higher (special materials)
Requires a controller?	No (optional)	Yes (solar controller)

Most common mistakes when selecting a pump

From our experience with dozens of customer cases, we know that the most common mistakes are as follows:

Installation of a standard UPS in a solar circuit – Leads to seal failure within 1–3 seasons. Glycol degrades standard rubber and high stagnation temperatures complete the damage. The pump then leaks, or gets jammed and the collectors overheat.
Too small a pump for a solar system – A customer buys a Solar 15-80 for a system with 6 m² of collectors at a height of 7 m and long pipes. The flow is insufficient, the temperatures in the tank are low, and the system appears non-functional. In fact, a Solar 25-120 would be sufficient and the problem disappears.
Overdimensioned UPS for a small radiator system – An UPS 25-80 in a house with three radiators runs in the left part of the curve (low flow, maximum pressure), which causes noise, cavitation and unnecessary consumption. The correct choice is UPS 25-30 or UPS 25-40.
Forgetting the expansion vessel in the solar circuit – The pump alone does not ensure the safety of the circuit. Solar glycol expands significantly at temperatures of 100–130 °C and without a properly set expansion vessel and safety valve, there is a risk of pipe rupture or valve failure.
Wrong shaft distance – Solar 15-80 has a shaft distance of 130 mm, Solar 25-120 has 180 mm. If you buy the wrong one, the pump will not fit into the mounting station and you will have to solve the reduction or return the product.

For selection and troubleshooting, also see the other articles: Common Grundfos pump faults and how to fix them and Grundfos pump not pumping or making noise – causes and solutions.

Maintenance of both types of pumps

UPS pumps are almost maintenance-free. Every year during the annual heating system inspection, check:

The temperature of the pump body (it should not be cold – that would mean the medium is not flowing)
Vibrations and noise – any grinding or rattling indicates rotor wear
Sealing of connections and flanges
Speed setting – after the heating season ends, you can switch to level 1 as a test, and back to level 2 in the autumn

Solar pumps require a similar annual inspection, plus the following:

Every 2–3 years, check the quality of the glycol mixture (pH, freezing point, color) – degraded glycol corrodes metal and damages seals
Check the expansion vessel (pre-charge, membrane)
Check the safety valve – it is recommended to manually open and close it once a year to prevent it from sticking

More about regular inspection can be found in the article Maintenance and service of Grundfos pumps – what to check every year.

Most frequently asked questions (FAQ)

Can I put a standard UPS pump into a solar system if I have it at home as a spare?

No. This is one of the most common temptations and almost always ends in failure within one to two heating seasons. Glycol in concentrations above 30 % and temperatures close to stagnation (100–130 °C) quickly degrade the seals of a standard UPS. The result is a leaking pump or its complete jamming. Always use a pump designed for solar media – for example, GRUNDFOS Solar 15-80 or Solar 25-120.

What is the difference between Solar 15-80 and Solar 25-120 and how to choose?

The digits indicate the DN assignment (15 = 1/2" = smaller pipe, 25 = 1" = standard) and the maximum head (80 = 8 m H₂O, 120 = 12 m H₂O). Solar 15-80 with a 130 mm center-to-center distance is suitable for smaller systems with collectors up to 4–5 m² at heights up to 5–6 m. Solar 25-120 with an 180 mm center-to-center distance can handle collectors of 6–12 m² and higher elevations. Also, check the center-to-center distance – it must match your mounting station.

Can I operate an UPS pump without a thermostatic control, i.e., to run continuously?

Yes, UPS pumps are designed for continuous operation. Most simple heating systems with a gas boiler do exactly that – the pump runs while the thermostat turns off the boiler. In more modern systems with thermostatic valves on radiators, it is recommended to also use thermostatic control of the pump operation to save energy. In any case, the pump is not designed for frequent short cycles (e.g., turning on and off every 2 minutes) – this shortens the motor's lifespan.

What if the solar pump is running, but the tank temperature is not rising?

The most common causes: air in the solar circuit (needs to be bled), low media pressure (below 1 bar – needs to be topped up), faulty or incorrectly set controller (check T1/T2 sensors and the differential temperature setting), or the heat exchanger in the tank is clogged with deposits (needs to be flushed). If the pump is humming without visible flow, the rotor may be seized – turn it off, let it cool down, and try to loosen the screw on the front side of the pump. More information in the article Common Grundfos pump faults and how to fix them.

Is a Solar pump more expensive and why?

Yes, Solar pumps are 30–80% more expensive than a comparable UPS. The reason lies in the material solution: PTFE/EPDM seals, rotor made of temperature-stable polymers, stainless steel shaft, and in higher models, an EC motor with electronic control. However, these costs are justified – a properly installed Solar pump will last 10–15 years without problems in a solar system, while a cheap UPS improperly connected to a solar circuit will not last even 3 seasons.

Where can I find more information on choosing the right pump for my specific home?

On the atria.sk website in the Knowledge Center, you will find further articles: How to choose the right Grundfos circulation pump for heating, What Grundfos pump capacity do I need for my home, or Common questions about Grundfos pumps. For technically more complex projects (combination of heat pump, solar circuit, and heating system), we recommend consulting with a specialist – dimensioning without calculation is a gamble.

Conclusion – which pump is right for you?

If you have a classic heating system with a boiler – gas, electric, or pellet – and are looking for a reliable, low-maintenance circulation pump, choose one of the UPS models. For a small family home with traditional radiators and a power output up to 12–15 kW, the GRUNDFOS UPS 25-30 is a proven and cost-effective choice found in thousands of households.

If you have solar collectors on your roof or plan to install them, never skimp on the pump. The primary solar circuit is an extremely demanding environment, and only pumps certified for operation with a glycol-water mixture at high temperatures – specifically Solar pumps – are suitable. If you have any questions, feel free to contact us: