What does Monoblock heat pump mean?

All components (compressor, heat exchanger, refrigerant parts) are in one outdoor unit. Only hot water reaches the house via insulated pipes.

What are the differences between Monoblock and Split?

In Split, the evaporator is outside and the compressor inside, with a refrigerant connection. Monoblock doesn't need an F-Gas certified technician for connection, as no refrigerant enters the house.

Monoblock vs Split Heat Pumps: The Ultimate Comparison Guide

You have made the big decision. You did your research, saw the enormous savings, and decided to upgrade your home with a Heat Pump. You call the installer or engineer for a quote, and suddenly they ask: "Would you like a Monoblock or Split unit?"

If you felt a slight "freeze" hearing those terms, don't worry. It is the most common dilemma in the world of modern HVAC.

Both technologies do exactly the same job (produce hot or cold water with tremendous savings), but they differ fundamentally in how they are installed, how much space they require, and how they protect against frost. Let us analyse the pros and cons of each solution, so you can choose the one that perfectly suits your home.

1. What Is a Monoblock Heat Pump?

The word says it all: Mono-block (One piece). It is a single unit placed exclusively outdoors (balcony, roof or garden). Inside this "box" you find everything: the compressor, the refrigerant (freon), and the hydraulic components (circulator pump and heat exchanger). This means the radiator water exits the house, travels to the Monoblock unit, gets heated, and returns inside.

Monoblock heat pump - single outdoor unit with integrated hydraulics

🏠 Saves Indoor Space

No indoor unit (Hydrobox) is needed. Ideal for small apartments in Athens or Thessaloniki that have no available utility room or boiler closet.

🔧 Easier and Cheaper Installation

Because the entire refrigerant circuit is factory-sealed from the factory, no refrigerant piping is required. Installation can be carried out by a qualified plumber (simply connecting water pipes), cutting labour costs.

🛡️ Refrigerant Safety (R290)

New-generation pumps use the highly efficient but flammable propane (R290). In a Monoblock design, because all the refrigerant stays outdoors, there is 100% safety.

⚠️ The Frost Risk

Since the heating water circulates through outdoor pipes, what happens if the power is cut for hours in the winter at -5°C? The water will freeze, expand, and crack the unit's heat exchanger - damage costing thousands of euros. Solution: A competent installer will fit mandatory anti-freeze valves (which automatically drain the water if the temperature drops dangerously) or use anti-freeze fluid (glycol) in the circuit, which however slightly reduces system efficiency.

2. What Is a Split (Two-Part) Heat Pump?

Just like wall-mounted air-conditioners, the Split system is divided into two parts: an outdoor unit (with the fan and compressor) and an indoor unit (the so-called Hydrobox), which looks like a wall-hung gas boiler. The key difference: the water never leaves the house. The outdoor unit sends the hot refrigerant via copper pipes to the indoor unit, where the heat exchange takes place.

Split heat pump - outdoor unit and indoor Hydrobox

❄️ Zero Frost Risk

Even if the temperature drops to -15°C and the power is cut for days, there is absolutely no problem, since only refrigerant (which does not freeze) circulates outdoors - not water.

📦 Smaller Outdoor Unit

Because the hydraulic components (circulator, expansion vessel) are housed in the indoor unit, the outdoor machine is more compact in dimensions.

🏔️ Ideal for Northern Greece and Highlands

The ultimate choice for regions with harsh winters (e.g. Kozani, Florina, mountain villages).

💶 More Expensive Installation and F-Gas Requirements

Installation cannot be done by a plumber alone. A licensed refrigeration technician is required to braze copper pipes, perform a vacuum procedure, and charge the system with refrigerant (F-Gases). This significantly increases both time and installation cost.

🏗️ Requires Indoor Space

You need to find an area in the hall, bathroom, or utility room to mount the Hydrobox, which is similar in size to a wall-hung gas boiler.

3. Final Verdict: What Should the Engineer and the Homeowner Choose?

In terms of energy efficiency (COP), the top models perform equally well whether Monoblock or Split. The decision is based purely on the building's architecture and the local climate.

Selection guide Monoblock or Split by climate zone and building type

✅ Choose Monoblock if:

1. You are renovating a city apartment (Attica, islands, southern Greece) where hard frosts are rare. 2. You have no available indoor space for an indoor unit. 3. You want a faster and potentially cheaper installation. (Don't forget to insist on anti-freeze valves!)

✅ Choose Split if:

1. You live in Northern Greece or a highland area where temperatures frequently fall below zero. 2. You have a utility room, storage or large bathroom for the Hydrobox. 3. You are building a new house, where copper pipes can easily be hidden inside the walls.

➡️ Next Step

Whichever technology you choose, the machine must work flawlessly with the emitters you have (or plan to install) inside your home. How do you know if your heat pump can handle your old radiators? In our next article, we analyse one of the most critical technical terms you need to know: Low, Medium and High Temperature Heat Pumps.

Air-to-Water Heat Pumps: How They Work Low, Medium & High Temperature Heat Pumps Inverter Compressors & Refrigerants R32, R290: Safety Guide Heat Pump Sizing: The Danger of Oversizing

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