Question 1

What is MVHR?

Accepted Answer

Mechanical Ventilation with Heat Recovery (MVHR) continuously extracts stale, humid air from bathrooms and kitchens and supplies filtered fresh air to living areas and bedrooms, transferring heat between the two air streams so incoming air arrives close to room temperature. It's the standard way we ventilate an airtight home without losing the energy used to heat or cool it.

Question 2

How does MVHR work?

Accepted Answer

A central unit (or decentralised units) draws stale air from wet rooms and pushes it through a heat exchanger core, where most of its heat is transferred to incoming fresh air before the stale air is expelled outside. The warmed, filtered fresh air is then ducted to bedrooms and living areas, without the two air streams mixing.

Question 3

Do I need MVHR?

Accepted Answer

If your home is built or renovated to a reasonably airtight standard, yes. Sealing a home stops draughts, but it also traps the moisture, CO₂ and pollutants that used to leak out through gaps. In the homes we've commissioned, that trade-off is exactly why MVHR is fitted alongside airtightness work, not as an afterthought — without it, an airtight home can develop condensation, mould and poor air quality.

Question 4

Can I retrofit MVHR into an existing home?

Accepted Answer

Yes. Existing homes can be fitted with full ducted systems, decentralised through-wall units for individual rooms, or a hybrid of both, depending on ceiling access, budget and which rooms need it most. On our Mount Gambier retrofit, a solid limestone home, we core-drilled a decentralised unit straight through the wall behind a false wall and membrane — there's usually a practical retrofit path even where full ducting isn't possible.

Question 5

What's the difference between ducted and decentralised MVHR?

Accepted Answer

Ducted MVHR uses one central unit and a network of ducts to serve the whole house — the most efficient option for new builds. Decentralised MVHR uses individual through-wall units in single rooms, with no ductwork, making it a practical option for apartments, additions, heritage homes or wherever ducting isn't possible.

Question 6

How much electricity does MVHR use?

Accepted Answer

An MVHR unit's fans typically draw a small, continuous load — comparable to a couple of LED downlights — because they only need to move air, not heat or cool it. Because the heat exchanger recovers most of the energy already in the outgoing air, running MVHR costs far less than the heating or cooling it saves.

Question 7

How often should MVHR filters be changed?

Accepted Answer

Most units need filter replacement every 6–12 months depending on the model and local air quality. We recommend checking filters at the 6-month mark and replacing them at least annually — it's the single most common maintenance item we find neglected when we're called out to a unit we didn't originally install. Replacement filters are available for all units we service, regardless of brand.

Question 8

Can I clean MVHR filters myself?

Accepted Answer

Coarse pre-filters (G-class) can usually be vacuumed. Fine filters (F7 and similar) should be replaced rather than cleaned — cleaning damages the filter media and reduces its ability to capture fine particulates and pollen. We stock replacement filters for all major MVHR brands.

Question 9

Can I open windows with MVHR installed?

Accepted Answer

Yes — MVHR doesn't lock windows shut, and opening them occasionally won't damage the system. But the whole point of MVHR is that you shouldn't need to: it's designed to supply continuous fresh air without the heat loss, noise, security risk or pollen that comes with open windows.

Question 10

Does MVHR remove humidity?

Accepted Answer

MVHR continuously extracts moisture-laden air from bathrooms, laundries and kitchens, which is the biggest factor in controlling everyday humidity. It doesn't actively dehumidify supply air the way a dedicated dehumidifier does, but by constantly removing wet air at the source, it keeps average indoor humidity in a healthier range.

Question 11

Does MVHR cool the house?

Accepted Answer

No. MVHR's job is air quality and moisture control, not temperature control — it exchanges heat between outgoing and incoming air but doesn't actively cool the home the way an air conditioner does. On hot days it still brings in outdoor-temperature air, so it works alongside a heating and cooling system, not instead of one.

Question 12

Can MVHR replace air conditioning?

Accepted Answer

No. MVHR ventilates the home and recovers heat between air streams; it isn't sized or designed to add or remove enough heat to condition a room. High-performance homes still need a heating and cooling system — usually a much smaller one than a leaky, unventilated home would need, because the envelope and MVHR are already doing so much of the work.

Question 13

What happens during a power outage?

Accepted Answer

MVHR fans stop, so active fresh air supply and extraction pause until power returns. An airtight home will still have some background air change through the envelope and any openable windows, but for extended outages, opening a window periodically is a reasonable short-term fallback until the system is running again.

Question 14

Is MVHR noisy?

Accepted Answer

A correctly designed and commissioned system should be barely audible — quiet, even airflow from supply and extract terminals is one of the signs a system is running properly. When we're called out to a noisy unit, it's almost always a dirty filter, worn fan bearings, an undersized duct or a system that was never properly balanced at commissioning.

Question 15

Why do I need MVHR if my home isn't Passive House?

Accepted Answer

MVHR isn't a Passive House exclusive — any home built or renovated to a reasonably airtight standard benefits from it, and NCC 2022 now links ventilation requirements to airtightness results for all new SA homes, not just certified projects. The tighter the envelope, the more a home relies on mechanical ventilation to stay healthy.

Question 16

Does NCC 2022 require MVHR?

Accepted Answer

NCC 2022 doesn't name MVHR specifically, but it links a home's mechanical ventilation requirements to its blower door result: homes that test below 5 ACH50 trigger a mandatory mechanical ventilation calculation. In practice, that calculation is very often satisfied with an MVHR system, especially as SA builds get tighter.

Question 17

What size MVHR unit do I need?

Accepted Answer

Unit size depends on the home's floor area, number of bedrooms and wet rooms, and airtightness level — it's a design calculation, not a rule of thumb. Undersizing leaves rooms under-ventilated; oversizing wastes energy and money. We size and design systems as part of our MVHR service, and it's a step we won't skip even under time pressure on site.

Question 18

Why does my home feel stuffy without proper ventilation?

Accepted Answer

A stuffy feeling, especially overnight in bedrooms, is usually a sign of rising CO₂ from an airtight room with no fresh air supply. Levels build quickly with the door and windows closed, and are linked to poor sleep and morning headaches — problems that largely disappear once a room has continuous mechanical ventilation.

Question 19

Can high CO₂ make me feel tired or give headaches?

Accepted Answer

Yes. CO₂ concentrations that build up in a closed, airtight bedroom overnight are strongly linked to poor sleep quality, grogginess and headaches on waking. It's one of the most common — and most fixable — indoor air quality complaints in modern airtight homes without adequate ventilation.

Question 20

Why are my bathrooms damp even with an exhaust fan?

Accepted Answer

Many exhaust fans installed in new homes don't move enough air to meet NCC 2022's requirements, or aren't ducted correctly to outside, so steam and humidity linger long after a shower. It's one of the more common issues we're called out to diagnose — a correctly sized and commissioned ventilation system, whether a compliant exhaust fan or MVHR extract point, clears a bathroom in minutes, not hours.

Question 21

Are range hoods a problem in airtight homes?

Accepted Answer

A powerful range hood can extract more air than an airtight home can easily replace, creating negative pressure that pulls air back through gaps, worsens draughts, and can backdraft flued gas appliances like heaters or hot water systems — a genuine safety risk. Airtight homes need a makeup air strategy matched to the hood's extraction rate.

Question 22

What is makeup air and do I need it?

Accepted Answer

Makeup air is fresh air deliberately introduced to replace what a range hood extracts, preventing the negative pressure that causes backdraughting and makes doors hard to open. Whether you need a dedicated makeup air system depends on your hood's extraction rate and how airtight your home is — our calculator gives a quick estimate.

Question 23

Do you service MVHR units you didn't install?

Accepted Answer

Yes. We service, commission and maintain MVHR units from most major brands, regardless of who originally installed them. Contact us with your unit's make and model and we can advise on servicing options.

Question 24

My MVHR is making noise — what should I do?

Accepted Answer

Unusual noise usually points to a dirty filter, worn fan bearings, a loose duct connection or an object caught in a duct. It's worth investigating promptly, since running a struggling unit for longer can cause further damage. Book a diagnostic visit and we'll identify and fix the cause.

Question 25

How do I know if my MVHR system is running correctly?

Accepted Answer

A healthy system delivers quiet, even airflow from supply terminals, consistent extract from bathrooms and the kitchen, no unusual odours and no condensation on cold surfaces. If any of that feels off, it's worth booking a diagnostic visit before a small issue becomes a bigger one.

Ventilation & Indoor Air Quality