The ZETX series is our best-selling lineup — air-to-water monoblocs with an inverter-driven Copeland compressor and Siemens control. We manufacture it in two versions: ZETXe (External) and ZETXi (Internal). Technically they are identical — the only difference is where they are installed.
ZETXe — installed outdoors
The ZETXe sits on an outdoor pad or stand. It connects to the house through two pipes (heating water flow and return) and a power cable. It takes up no space inside the building.
- 3 output variants: 7, 10 and 15 kW
- Easy access for servicing and maintenance
- Supplied with a switchboard, optionally with a hydromodule
The outdoor unit is visible from the garden and its fan is audible in the immediate vicinity — something to keep in mind if neighbours are close by.
ZETXi — a genuine game-changer, because it sits inside
The ZETXi is placed in a utility room, basement or plant room. Air is brought in and exhausted through insulated ductwork that passes through the wall, terminating in weather louvres on the facade. Nothing is visible outside, nothing is audible outside.
- 3 output variants: 7, 10 and 15 kW
- Integrated switchboard with a complete hydromodule — circulation pump, electric backup heater and a three-way valve for domestic hot water. Nothing needs to be purchased separately; everything is built into the unit.
- Radial fan — a quieter construction compared with the axial fan used in the outdoor version.
- Significantly quieter for the surroundings — noise from an indoor unit splits into two components: the airflow hum at the facade louvres and the compressor buzz inside the building. Overall, the heat pump is quieter than its outdoor counterpart.
- Greater distance from neighbours — by placing the unit indoors, the noise source is physically moved away from the property boundary. This is a decisive advantage in densely built-up areas.
- Corner installation — one duct exits through one wall, the other through an adjacent wall. This disperses the sound in two directions rather than concentrating it towards a single neighbour.
- Enhanced condensation insulation to prevent moisture issues in the indoor environment.
- Ductwork required (a set of PUR panels for intake and exhaust, including wall penetrations and rain-proof louvres, approximately 20,000 CZK).
Advantages of indoor installation (ZETXi)
Placing a heat pump indoors brings a range of practical benefits that simply cannot be replicated with an outdoor unit.
Weather protection — the heat pump is never exposed to rain, snow, frost or wind. This extends the equipment’s lifespan and reduces both the cost and frequency of service interventions. There is no ice build-up on the housing, no UV degradation of plastics, and no debris accumulating around the unit.
Lower running costs and maintenance — a unit shielded from extreme weather requires minimal upkeep and retains full performance for longer. Outdoor units, by contrast, endure thermal cycling, corrosive moisture and seasonal fouling of the heat exchanger.
Factory-sealed refrigerant circuit — in a monobloc design (both ZETXe and ZETXi), the entire refrigerant circuit is brazed and pressure-tested at the factory. Split systems, on the other hand, route refrigerant piping from the outdoor unit through the wall to an indoor module, with field-made joints at each end. Every field joint is a potential leak point. A factory joint is always more reliable than one made on site. As a result, periodic leak testing required under F-gas regulations is typically unnecessary for monoblocs.
Cleaner facade — an indoor monobloc requires fewer penetrations and structural modifications to the building envelope compared with an outdoor unit that needs pipe runs, cable trays and wall brackets. This matters especially when retrofitting older buildings where every hole in the insulation is a thermal bridge.
Better integration with the house — the unit tucks away in a plant room, basement or utility space. The facade stays clean and visually uncluttered — only the air-intake and exhaust louvres are visible from the outside.
ZETXe vs. ZETXi comparison
| Feature | ZETXe (outdoor) | ZETXi (indoor) |
|---|---|---|
| Placement | Outdoors on a pad or stand | Inside, in a utility / plant room |
| Connection to building | 2 pipes + power cable | Air ducts through the wall |
| Visibility from outside | Unit visible in the garden | Nothing visible |
| Noise impact on surroundings | Audible outdoors | Stays inside the building |
| Hydromodule | Optional (accessory) | Integrated, included in price |
| Switchboard | Separate (accessory) | Integrated, included in price |
| Condensation insulation | Standard | Enhanced |
| Fan type | Axial | Radial (quieter) |
| Indoor space required | None | Requires a utility / plant room |
| Ductwork | Not needed | Required (accessory, ~20,000 CZK) |
| Weather protection | Exposed to the elements | Fully protected indoors |
| Maintenance / lifespan | Standard | Extended, thanks to weather protection |
| Facade modifications | Pipe and cable penetration | Air louvres only |
What they share
| Feature | ZETXe | ZETXi |
|---|---|---|
| Type | Air-to-water | Air-to-water |
| Regulation | Inverter (variable-speed drive) | Inverter (variable-speed drive) |
| Heat-loss coverage | Up to 20 kW | Up to 20 kW |
| Cooling | Active (reverse cycle) | Active (reverse cycle) |
| Cascade | Yes | Yes |
| Defrost | Cycle reversal | Cycle reversal |
| Control system | Siemens | Siemens |
| Refrigerant | R454b (low GWP) | R454b (low GWP) |
| Refrigerant circuit | Factory-sealed (monobloc) | Factory-sealed (monobloc) |
| Energy class — heating | A+++ | A+++ |
| Energy class — cooling | A++ | A++ |
When to choose which variant
ZETXe is a good fit when:
- You have space in the garden for an outdoor unit
- You prefer a simpler installation without ductwork
- Your utility room is small or non-existent
ZETXi is a good fit when:
- You do not want a visible unit on the property
- You need to minimise noise for neighbours
- You have a spacious utility room with the option for wall penetrations
- You value a fully integrated solution with no additional accessories to buy (hydromodule and switchboard are included)
- You want to extend the heat pump’s lifespan by protecting it from the weather
- You prefer a clean facade with no outdoor unit in sight
Summary
ZETXi is a game-changer for anyone who cares about noise. The overall sound level is lower and it is split between a gentle hum at the facade louvres and a muffled buzz inside the plant room. With a corner installation — ducts exiting through two perpendicular walls — the sound is dispersed even further. And crucially, by moving the heat pump indoors, the noise source is automatically moved further from the neighbour’s boundary. On top of that, indoor placement shields the unit from the weather, extends its service life and reduces maintenance demands.
Both variants heat, cool and produce domestic hot water. Both carry an A+++ energy rating for heating and include a webserver for remote management. The difference comes down to where the unit physically stands — and what that means for installation, noise and long-term upkeep.
Need help deciding? Get in touch — we will recommend the right variant for your home.