HIUs & Traditional Boilers: What you need to know
HIUs & Traditional Boilers: What you need to know
The differences, details and what to look out for in HIU and Boiler Setups
In the plumbing trade, it’s essential to stay informed about the types of heating systems you're likely to work with.
Whether you’re installing, servicing, or maintaining them, Heat Interface Units (HIUs) are becoming a common alternative to traditional gas or electric boilers — especially in new-build flats and housing developments with district or communal heating systems.
Whether you're an experienced professional or just starting out, this guide outlines the key differences between HIUs and conventional boiler systems to help you stay ahead in the field and understand what each setup means for your day-to-day work.
About Altecnic:
Altecnic is the UK’s trusted name for plumbing components, serving the trade for every kind of system.
As part of the internationally renowned Caleffi Group, we supply everything from: pressure reducing valves, expansion vessels, and radiator valves to Heat Interface Units, heat pump accessories, and components for renewable systems.
HIUs vs. traditional boilers: What do they do?
Both Heat Interface Units and traditional boiler systems are used for the same purpose: to heat water and circulate this around a plumbing pipe system as necessary.
The key difference between HIU and traditional boiler systems is in how and where the system water is heated.
Boiler systems: how they work
Traditional boilers, whether gas, electric, or combi, are standalone heating systems installed in each individual property. They provide hot water for central heating (via radiators or underfloor heating), and domestic hot water (DHW) (for showers, baths, sinks, etc.).
When you turn on the heating or run a hot tap, the boiler kicks in to heat water. Depending on the setup, this hot water is either circulated through a sealed central heating circuit, delivered directly to taps as potable water.
Common types of boiler systems you will encounter:
| Boiler Type | Key Features | Typical Use / Suitability |
|---|---|---|
| Combi Boilers |
|
Smaller homes with lower simultaneous hot water demand |
| System Boilers |
|
Homes with multiple bathrooms or higher hot water usage |
| Conventional Boilers |
|
Older homes, low water pressure situations, complex system upgrades |
| Industrial Boilers |
|
Factories, hospitals, processing plants; not for domestic use |
On-demand hot water with boiler setups: How it works
In combi systems, water is heated instantly as it flows through the boiler via a plate heat exchanger, no storage needed.
In system and conventional setups, hot water is pre-heated and stored in a cylinder. Once the stored supply is used up, you'll need to wait for it to reheat, either via the boiler or an immersion heater (which acts as a backup).
HIU setups: how they work
Heat Interface Units (HIUs) are used in properties connected to a communal or district heating system. Unlike traditional boilers, HIUs don’t generate heat themselves. Instead, they act as a bridge between the building’s internal plumbing and a central energy source.
They receive pre-heated water from a central plant which is then used to provide:
- Space heating (via radiators or underfloor systems)
- Hot water for taps, showers, and baths
If you’re new to communal heating systems and district heating systems, you may be wondering how HIUs work and why they exist compared to boiler setups. To answer these questions, we must look at what the different heating systems do and how they work with different building types.
Communal heating systems
Communal heating systems provide heat and hot water to multiple properties from a single central source. They are typically used to heat a single building or a closely connected group of buildings.
Uses include:
- Apartment blocks and residential flats
- University campuses
- Hospitals and healthcare facilities
- Commercial or mixed-use buildings
Communal heating systems differ from traditional boiler setups, especially in apartment blocks and flats where multiple individual boilers would otherwise be needed. By centralising heat generation, they enable more energy-efficient heating and hot water supply. Flats draw hot water on demand when needed, reducing water and energy waste, and improving convenience.
District heating systems
District heating systems provide heat and hot water from a central energy source to multiple buildings or even entire neighbourhoods via an extensive network of insulated pipes. Unlike communal heating, which usually serves a single building or a closely connected group of buildings, district heating operates on a larger scale, distributing thermal energy over a wide area.
The central heat source can include boiler houses, combined heat and power (CHP) plants, waste-to-energy facilities, or renewable energy centres. Heat is generated at this central plant and transported through the district heating network to the connected properties.
District heating is typically used in:
- Housing estates and large residential developments
- Business parks and commercial districts
- Industrial zones and public service buildings such as schools and hospitals
What HIUs mean for property owners
HIUs allow residents to control when they receive heated water and how much of it, much like traditional boilers. However, HIU-based systems come with several advantages over individual boiler setups:
- Energy Efficiency: Centralised heat generation tends to be more efficient, reducing overall energy consumption and carbon emissions.
- Space Saving: HIUs are compact and wall-mounted, freeing up valuable space inside the property compared to larger boilers and hot water tanks.
- Reduced Maintenance: With heat generation managed centrally, individual properties avoid the complex maintenance tasks typically associated with boilers.
- Improved Safety: Since no fuel combustion occurs on-site, risks related to gas leaks or carbon monoxide are eliminated within individual properties.
- Flexible Control: Residents can still enjoy personalised control over their heating and hot water timing and temperature, similar to traditional systems.
- Future-Proofing: HIUs are compatible with low-carbon heat sources like biomass, heat pumps, or waste heat recovery, making them well-suited to evolving energy policies and sustainability goals.
HIUs & Boilers: A side by side comparison
| Feature | Heat Interface Units (HIUs) | Traditional Boilers |
|---|---|---|
| Heat Source | Centralised heat plant (communal or district heating) | Individual gas, electric, or oil boilers in each property |
| Heat Generation Location | External to the property, heat transferred via heat exchanger | Inside each property, boiler heats water on demand or stored |
| Space Requirements | Compact, wall-mounted units | Larger footprint, especially conventional boilers with tanks |
| Maintenance | Central plant maintained by specialists, minimal onsite upkeep | Individual boilers require regular onsite servicing |
| Control & Billing | Individual metering enables accurate heat usage billing | Typically flat-rate or boiler-specific metering |
| Hot Water Availability | Depends on central plant and HIU controls, generally on-demand | Instant (combi) or stored hot water (system/conventional) |
| Installation Complexity | Requires connection to communal/district heating network | Standard plumbing installation per property |
| Safety | No combustion onsite, reduced risk of gas leaks or CO (carbon monoxide) poisoning | Combustion onsite, requires ventilation and safety checks |
| Environmental Impact | Potential for lower carbon footprint through centralised efficiency | Varies widely by boiler fuel and efficiency |
| User Control | Resident controls heating & hot water flow and temperature | Resident controls boiler heating and hot water settings |
| Scalability | Ideal for multi-unit buildings, new developments | Better suited to standalone homes or small properties |
The parts you need for HIU systems
Whether you’ve been tasked with a job that has one in, or are contracted to install them, you may need to source parts for a new HIU system.
Whether its your first time or just another project, Altecnic has you covered, we offer a range of HIUs and HIU accessories, including:
Altencic HIUs:
- SATK32 Indirect HIU with Network Protection and Integral Room Controller: An advanced electronic HIU offering instantaneous hot water production and space heating control.
- SATK22 Direct HIU: A versatile HIU suitable for low, medium, and high-temperature systems. It allows independent control of heat regulation and domestic hot water production within centralised heating systems or district heating networks.
Explore our full range of HIUs here.
HIU Accessories:
- Thermostatic Mixing Valves (TMVs): These valves maintain safe, controlled hot water temperatures to prevent scalding.
- Pressure Reducing Valves (PRVs): Designed to reduce water pressure and maintain it to a set level, preventing damage to components installed downstream.
- Expansion Vessels: These vessels absorb pressure fluctuations in the heating system, protecting components and improving longevity.
- Mounting Rails
- Secondary Isolation Ball Valves