How does heat recovery work

It’s a relatively new phenomenon in Ireland, so here we’ll answer the frequent question of “how does heat recovery work” and why it might be of benefit to you and your family.

Heat exchanger

The warm air from your house is extracted up through ducting into a counter-flow heat exchanger. The exchanger plates warm air up as the stale air passes over them.

Simultaneously, the supply fans are bringing cool fresh filtered air into the exchanger. This air is warmed and distributed through ducting to the dry rooms.The exchanger is manufactured so that there is no cross contamination of the exhaust air and the supply air.


A mechanical ventilation with heat recovery has to operate in many different conditions. In winter the heat exchanger is working to ensure that heat from the dwelling in not lost through extraction (figure 1).

In spring and autumn, conditions may occur where heat recovery is not required. If it is warmer indoors than the preset comfort temperature, yet the outside temperature is lower, the bypass will open automatically so that the cooler outdoor air bypasses the heat recovery function and lowers the internal temperature (figure 2). The same method also applies during cool summer nights, which is why the feature is ofter know as “Summer Bypass”.

What sets Zehnder ComfoAir units apart is that Summer Bypass does not mean filter bypass. With ComfoAir, the incoming air continues to be filtered before it is supplied to the home when the bypass is open. This is especially important for allergy suffers in the hay fever season!

However, during hot summer days, we aim to keep the heat outside whilst ventilating to maintain a balanced system and ensure indoor air quality remains high. In this situation, the bypass would stay closed so that the fresh air enters the home but not the heat (figure 3).

New Zehnder ComfoAir Q units come with a modulating bypass which enables you to control the heat recovery. Regulated by sensor technology it is now possible to open the by-pass valves for maximum heat recovery, close them for no heat recovery or partly close them for limited heat recovery. For the end user this means more comfort through optimised temperature control as well as user friendliness due to its automatic and intelligent control for a worry-free operation.

Housing situation and looming prospects for the future

Fresh air is vital for our health. Scientific studies prove that there is a direct relationship between our performance and well-being, and a regulated fresh air supply.

When we fast forward to the new homes being built today, 2010 Building Regulations call for high levels of insulation, air tightness and double glazing to trap the sun’s heat. It is easy to see that the future demands more and more energy efficiency to meet the nearly Zero Energy Buildings (nZEB) standards.

While ensuring low energy consumption, modern homes on their own do not guarantee the natural air exchange that was historically provided by accidental ventilation through Heavyweight materials, low levels of insulation and gabs in the envelope. Moreover there are buildings in which the windows often remain closed due to noise or dust particles.

This is where we need a ventilation system which has optimal dimensions and which ensures a constant supply of fresh air in all internal spaces. Ventilation Systems with heat recovery can provide you with ideal solutions for a comfortable, healthy and energy-efficient indoor-climate.

View Versatile’s heat recovery & ventilation systems here.

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