Ventilation Systems

Ventilation systems are a polarizing topic. Ask anyone with a small amount of knowledge and they will argue strongly in one direction or another.

DISCLAIMER: I am not an employee of any company mentioned below, nor am I an expert in ventilation systems, or anything related. All this is material is from my own research and personal opinion unless specifically stated otherwise. 

The purpose of ventilation

Ventilation systems are designed to increase fresh airflow around your home. This will help keep air fresh as well as dry the air which will result in reduced condensation and mold. Also dryer homes are easier to heat.

It is important to know that the purpose of a ventilation system is not to heat your home (no matter what ventilation company suppliers may tell you). If you want to heat your home, buy a heat pump, which is a much cheaper and more efficient method of heating.

Some would argue that opening a window does as much good as a dedicated ventilation system, but there are many other factors that impact this. Sometimes opening a window is not always possible, or if the window is on a south facing wall, it may not help much at all. If someone is home during the day in winter, having the windows open is not preferable. For rental properties, it may not be possible to enforce windows are opened, so ventilation systems can give land lords piece of mind.

Others argue that a dehumidifier does a better job of drying the air in your house. They are not wrong but this does not solve the fresh air problem and they also require clearing water frequently, additional power and floor space for the appliance.

Often people will refer to an Otago University study to claim that ventilation systems provide no added value. The study only considered the use of ventilation for heating and cooling and not its primary purpose of ventilating a home and reducing moisture. It also only tested in a single house in Dunedin, and calculated results for other cities using simulations.

Sales people may also argue that ventilation systems help reduce allergens in the air. I have no clear evidence for or against this statement.

Note, that airing out a home is one of the EECA recommended 3 Essentials For A Healthy Home. Ventilation systems are just one of the options it suggests to meet this requirement.

Types of ventilation systems

There are two types of ventilation systems. Heat Recovery Ventilation or Positive Pressure Ventilation. (Three if you classify opening a window as a ventilation system)

Heat Recovery Ventilation (HRV)

Not to be confused with the brand HRV, who actually supply a Positive Pressure Ventilation system (yes, I agree this is very misleading). 
HRV systems work by recovering some of the heat lost by pushing the warm air out and pushing it back into the home.
These types of systems are more relevant for houses in colder climates than Auckland, where the houses are sealed tight and it is very difficult for air to escape.

..[HRV systems] are actually designed for VERY cold dry environments, like Canada…triple glazing and a furnace / central heat working 24/7 for 6-8 months of the year…oh and its -25 degrees outside. NZ doesn’t need this type plus its too damp (When its very cold it’s very dry)…

SmartVent (Synergy), DVS (Recalim), Cleanaire and MoistureMaster make HRV systems.

HRV systems are generally more expensive than PPV Systems.

Positive Pressure Ventilation (PPV)

Positive Pressure Ventilation systems work by taking (fresher) air from the ceiling space and pushing it though into house, and forcing older air out though small gaps in the outside walls and joinery.

Another advantage of PPV systems, is that when the air in the ceiling space is warmer, it provides a small amount of heating in the early evening. If you’ve been into the ceiling space in a steel roof home, you know how hot they can be. Some PPV systems take advantage of this by pushing this warmer air into the home up to a set temperature, keeping the house warmer for longer. This may not be as much of an advantage in houses with tile roofs.

Most PPV systems offer an optional Summer Feature which allows the system to bring in fresh air from outside instead of using the hot air from the ceiling space. The value of this addition can depend on your setup.

“summer feature” (to supply cool air from outside during summer) is useless in houses with steel roofs because the air is heated by at least 8C degrees while it travels over ducts, even with insulated ducting..

Most PPV systems also offer an optional Heat Transfer Kit which allows warm air from one room to be distributed to other rooms in the house. These are more suitable for houses with a wasteful form of heating (IE fireplace). For more efficient forms of heating (such as a heatpump) these are not as effective as the two systems fight against each other.

HRV, DVS, SmartVent and Unovent are companies that do this type of ventilation

Some informed discussion on the difference between HRV and PPV ventilation systems can be found here:

The Contenders

System Type Filter Blocked Particles Installed DIY
HRV PPV F7 80-90% <2µm Yes No
DVS PPV F7 80-90% <2µm Yes No
Moisturemaster PPV EU4 (G4) 90%+ <5µm Yes No
Smartvent PPV F7 80-90% <2µm
(80-90% <0.4µm)
Yes Yes
Unovent PPV G4 (Resuable) 90%+ <5µm Third Party Yes
Moisturemaster HRV EU4 (G4) 90%+ <5µm Yes No
Cleanaire HRV EU3 (G3) 80-90% <5µm Yes No
Smartvent Synergy HRV F7 80-90% <2µm
(80-90% <0.4µm)
Yes Yes


HRV, despite their misleading name, only offer a PPV type system.  I had requested a quote from them a few years prior to my install for roughly $3500 for a four outlet, single fan system. HRV are notorious for being very pushy salesmen, and offering poor after sales support.


DVS is the other major competitor to HRV. They appear to offer both PPV (Classic) and HRV (Reclaim) type systems.


SmartVent is an all inclusive ventilation systems which include filter, fan, outlets and control box as well as all required ducting in a single box. It is made by Simx who also make Manrose fans, which is a popular brand. They can install for you, or can be purchased from a number of retailers around New Zealand.

Smartvent kits include an even number of outlets (SV02, SV04, SV06). For an odd number a rooms, an extension kit(s) can be added.

The Evolve comes with a tablet controller (as opposed to a wall controller) and provides additional temperature and humidity sensors to provide a higher level of control. The Evolve kit can be purchased separately or with kits ending with the E suffix.

Smartvent uses an F7 filter which will block 80-90% of particles as low as 2µm, although they claim 0.4µm on their own website. This should be small enough to block the majority of fiberglass particles that will be present in some ceiling spaces.


Unovent is another DIY option. It comes with individual outlets which can be installed separately. Each outlet has its own fan. This makes the system really easy to expand as outlets can be added as desired.

Each Unovent will include its own filter, each which will require changing and cleaning regularly. Unlike other systems, the filters are washable so there are no ongoing costs with the Unovent system.

Unovents use a G4 filter, which is able to block particles as low as 5µm, which may not be enough to block the fiberglass fibers used in ceiling insulation. It would be important to check this before considering Unovent.

Due to the simplicity of Unovent, it is not possible to get any Heat Transfer or Summer Feature functionality. Not a viable solution of you need them, or may need them in the future.

My Situation

I own a 3 bedroom 86m² house with HardiePlank cladding, steel roof and aluminium single glazed joinery in Central Auckland. We have a heatpump for the purposes of keeping the living area warm during winter and cool in the summer and use fan heaters in the bedrooms during winter.

With this setup, we continue to have some moisture problems. Condensation on windows and mold in the darker bedrooms. Because of this I decided to install a ventilation system.

Not willing to invest in the cost of a Heat Recovery system, I started looking into PPV systems to see what would be suitable. I liked the idea of being able to install myself. SmartVent and Unovent were the two obvious choices.

Although the convenience of separate Unovent fans was enticing, I ultimately chose the Smartvent system. This was mainly due to my fiberglass insulation as the Smartvent has the single, stronger filter. This would have been a much harder decision if Unovent provided their vents with F7 or better filters.

For my 4 room setup, I could have chosen the SV02 (recommended for houses less than 130m² with two additional extension kits) yet opted for the larger SV04 as for a 4 room setup as the SV02 is not recommended for 4 room setups as per the Selection Guide.


Installing the SV04 system seems relatively straight forward. The only requirement is to get an electrician to put a power point into the ceiling space. I opted to install the system first so I knew where the control box would end up and how much reach the power cord would have.

When installing the vents, it is important to keep the vent location as far away from doors and windows, but also 1m away from any wall. The vent location should be in a location clear of any ceiling batons or beams. I found this easier to do from above, but could just as easily be done from below with a stud finder.

The Fan should be at least 1m away from the first bend (and therefore first Y piece) and the filter should be at least 1m away from the fan. The SV04 box comes with 3x 6m lengths of insulated 150mm duct and 1x 6m length of insulated 200mm duct.

Apart from these considerations, it was a very straightforward install, taking a total of about 4 hours.


We’ve been running the SmartVent system for almost a year now. We noticed only a small amount of condensation on the windows during winter, although the 2017 winter was quite mild so may not be a true test of the system. Being designed for houses up to 260m², we keep the fan on the lowest setting.

As we enter summer, we are finding the house to be very hot. The house can be in the high 20s, but bringing in roof air is not viable as it can be as hot as 60 degrees up there. We are considering putting in a summer kit to bring in the cooler outside air (despite knowing these are not as effective in houses with metal roofs).


Summer Feature Update:

We committed and purchased the SmartVent Summer Feature kit. We paid extra to have it installed professionally, but the installer told me judging from my install, it would have been simple enough to install on my own.

Unfortunately, the Summer Feature has a major flaw where it will bring in outside air as the roof exceeds it’s maximum temp but has no temperature sensor of its own. This the the point where the system would normally shut off. However New Zealand is in the middle of a heatwave, and outside temperatures can be in the 30s. That air is not wanted inside, especially when I have Aircon running. So now I have to manually start and stop the system to only run at night, in order to stop the two systems fighting against each other. Not very Smart.

I also note that the Summer kit ducting is not insulated (unlike the rest of the system) which would mean that when the system brings in the cool(er) outside air, the very hot roof air will warm it up before it enters the house. This seems very counter intuitive to me.





3 thoughts on “Ventilation Systems

  1. I have found my Smartvent to not be very smart, as you say. The thing that bothers me the most is the fan never goes to zero if it is on Automatic mode. In the middle of summer with roof temps in the high 30s, the slowest the fan goes is speed 1.

    In the middle of winter when it’s cold it still insists on pushing that freezing cold air into our bedrooms. I can feel the chill even on the lowest fan setting.

    Consequently I have to constantly monitor it and either switch it off completely, or run it on timer mode.

    I’m considering Unovent for my rental property but I’m not sure what sort of timers or controls it has.

    Liked by 1 person

    1. Hmm maybe you have a different version than I had. I’m sure before I got the summer kit installed, the fan turned off completely when the roof temp reached the upper limit.

      I have no experience with unovent, but I don’t like the idea of multiple filters, and multiple power outlets required. And not sure on its control mechanism either.

      If I were to do this over again, I would simply avoid a PPV system and instead go for vented aircon (perhaps not for a rental though). I think combining into one system is much better than having two competing systems.

      Thanks for reading!

      Liked by 1 person

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