Comparison of Boilers with Instant DHW Heating
If you are choosing a condensing gas boiler with instant domestic hot water (DHW) heating for a flat or a smaller family house with one bathroom, you will very likely come across two of the best-selling names on the Slovak market: Protherm Gepard Condens 18/25 MKV and Viessmann Vitodens 100-W 25 kW. Let's put both models side by side.
Comparison table
| Parameter | Protherm Gepard Condens 18/25 MKV | Viessmann Vitodens 100-W, 25 kW |
|---|---|---|
| Boiler type | Wall-mounted gas condensing boiler, instant DHW heating | Wall-mounted gas condensing combi (instant) boiler |
| Rated heat output | 18/25 kW | 3.2 - 25 kW (wider modulation range) |
| Heat exchanger material | Aluminum alloy (new design) | Inox-Radial - stainless steel |
| Burner | - | MatriX burner |
| Max. DHW flow rate (at Δt 30 K) | 12.1 l/min | - |
| Control | Weather-compensated control option | - |
| Weight | 33.4 kg | - |
| Suitability | Flat/house with one bathroom, replacement of an older boiler | Flats and family houses with one bathroom |
Dashes in the table mean that the given parameter is not stated in the manufacturer's documentation, not that the boiler lacks that feature.
Heat exchanger - aluminum vs. Inox-Radial stainless steel
The condensate produced during operation is mildly acidic, so the exchanger material must resist corrosion long-term. The Protherm Gepard Condens uses a proven, more affordable aluminum exchanger. The Viessmann Vitodens 100-W is built on the Inox-Radial stainless steel exchanger, which is more resistant to the corrosive effect of condensate, resulting in a longer expected service life.
Output modulation range
Modulation means the boiler's ability to smoothly reduce and increase output according to current demand. The Viessmann Vitodens 100-W offers a range of 3.2 - 25 kW, i.e. a significantly wider range downward than typical boilers in this class - meaning less cycling (repeated switching on/off), especially in transitional periods. The Protherm Gepard Condens operates in the 18/25 kW class with a narrower range, which is entirely sufficient for normal operation in a smaller flat.
Who each model suits
Protherm Gepard Condens 18/25 MKV is a typical choice for a simple and affordable replacement of an old non-condensing boiler - its compact dimensions (480 × 895 × 360 mm) and weight of 33.4 kg allow installation even where an older unit was previously fitted.
Viessmann Vitodens 100-W 25 kW appeals to more demanding customers who value material quality, a longer expected exchanger lifespan and smoother control thanks to the wider modulation range.
You can find both models in the condensing boilers range at atria.sk. If you are not sure which output or exchanger type matches your consumption, we are happy to help you choose.