How Does a Heat Recovery Unit Work in a House?

A heat recovery unit allows a home to stay warm and well-ventilated without wasting energy. Instead of letting warm air escape through extractor fans or open windows, it captures that heat and uses it to warm the incoming fresh air.

Across Hampshire, Berkshire, Surrey, and Oxfordshire, this technology is becoming common in both new builds and renovations. Homeowners are using it to lower heating bills, reduce condensation, and maintain fresh indoor air all year round.

The Purpose of a Heat Recovery Unit

Every home produces heat from heating systems, cooking, and daily living. Without proper ventilation, air can become stale, damp, or filled with pollutants. Traditional extractor fans remove that air but also waste the heat it contains.

A Mechanical Ventilation with Heat Recovery (MVHR) system solves this problem. It keeps air moving through the house while recycling most of the warmth.

The Process in Simple Terms

1. Warm, stale air is extracted from rooms like kitchens, bathrooms, and utility spaces.
2. That air passes through a heat exchanger inside the central MVHR unit.
3. The heat is transferred to the incoming fresh air from outside.
4. The now-warmed, filtered air is distributed through ducts to living rooms and bedrooms.
5. The stale air exits the house without its heat.

The two air streams never mix, so you get fresh air without losing energy.

Main Components of the System

• Central unit containing fans, filters, and the heat exchanger
• Ductwork connecting each room for both supply and extract airflows
• Intake and exhaust terminals positioned on outside walls or roofs
• Control panel that allows manual or automated operation

When installed and balanced properly, the system runs quietly in the background with very little power consumption.

Example of How It Works in Practice

A recent installation in Reading involved a three-bedroom semi-detached house. Before MVHR, the home relied on window ventilation and extractor fans. After fitting the system:

• Fresh air now enters each bedroom and living room through ceiling diffusers.
• Extract ducts in bathrooms remove damp, humid air.
• The heat recovery unit recovers around 90% of the outgoing heat, keeping the home comfortable without drafts.

In Guildford, a property built in the 1980s saw similar results after a retrofit, with improved air quality and a noticeable drop in heating demand.

Energy Savings

A typical MVHR system can reduce overall heating energy use by 20–30%. While the fans consume some electricity, the recovered heat offsets far more than what is used.

This balance is why heat recovery systems are included in many new-build energy calculations under SAP assessments.

Why Air Exchange Rate Matters

Each system must be designed for the correct air exchange rate. Too low, and the home stays stuffy. Too high, and it wastes energy. A qualified installer uses property size, insulation levels, and occupancy to determine the right balance.

In most UK homes, air is exchanged once every two to three hours, ensuring a steady supply of fresh air without noticeable drafts.

Maintenance Requirements

Heat recovery systems require little maintenance:

• Replace or clean filters every six months.
• Have a full service annually to clean the heat exchanger and check fan performance.
• Ensure exterior vents remain unobstructed by leaves or debris.

All electrical work, including the power supply for the MVHR unit, must be installed and certified by a qualified electrician.

When It Works Best

The system is most effective in well-insulated and airtight homes. This includes:

• Modern builds with minimal air leakage
• Renovations with upgraded insulation and windows
• Garden cabins or offices that use air-tight construction methods

By reducing the need for window ventilation, MVHR keeps heat indoors while still delivering clean air.

Environmental Benefits

A heat recovery unit reduces both household energy use and carbon emissions. In the South East of England, a typical home can cut its annual CO₂ output by up to 300 kg by recovering and reusing heat that would otherwise be lost.

These savings help homeowners meet tightening energy efficiency standards under Building Regulations Part L and Part F.

Expert Design and Installation

Professional design ensures the ducting is well-planned and the system is quiet and efficient. Poorly designed systems can cause noise issues or uneven air distribution.

At ClimateWorks, we design and install MVHR systems across Hampshire, Berkshire, Surrey, and Oxfordshire. Every system is commissioned and tested to ensure compliance and performance.

References

• UK Government – Building Regulations Part F
• Energy Saving Trust – Home Ventilation
• CIBSE – Ventilation and Heat Recovery Guidelines

Author Bio

Dr Julian Carter is Technical and Compliance Director at ClimateWorks. He has over 25 years of experience in air conditioning, refrigeration, and ventilation, delivering projects across Hampshire, Berkshire, Surrey, and Oxfordshire. Julian also lectures as a visiting professor at a UK university, focusing on building services and low-energy ventilation design. His work ensures every installation meets the highest standards of safety, performance, and compliance.

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