For inexplicable reasons a doctrine of preferring “natural” ventilation prevails in NZ. Funny though, hardly anyone advocates “natural” laundry practices – for good reasons: a (washing) machine can do the job more efficiently, conveniently and environmentally friendly. Same goes for ventilation. “Naturally” ventilated buildings are usually either under- or over ventilated; additionally, there is no way to re-use the warmth of the outgoing air. As natural ventilation relies on weather and stack effects, it is impossible to control airways or amounts of air exchanged. Much like throwing your laundry in the river, and picking it up 2-3 km downstream, hoping that nature has sufficiently tumbled and spun the load.
Please note: mechanical heat recovery ventilation is not air conditioning; air is always fresh - not reused; you can open windows and doors as you please; fine tune to your hearts content; switch the system on and off as you wish. It is – unlike most mechanical ventilation systems on the market in NZ - a balanced system, meaning: there is no pressure differential between indoors and outdoors. A well designed system is silent, too, and can filter pollutants, allergens, and noise.
Yes, mechanical ventilation uses energy - but efficient systems need very little electrical energy to do a good job - plus true heat recovery models regain thermal energy from outgoing air, thus saving energy for heating the fresh air.
In cars, it is long understood that a mechanical ventilation system gives far better control of the in-car environment, than just relying on opening windows. In fact, I sometimes jump to the conclusion that New Zealanders are spending that much time in their cars, because there – unlike in their homes – they are able to maintain comfortable climate conditions. In a Passive House with mechanical heat recovery ventilation the comforts of home can truly be experienced; if this leads to a reduced recourse to the car – the better!

In Auckland, you probably would not have wanted to live in a house that relies solely on solar gains to be warm in recent weeks, because sunshine hours were rather rare. I take this as an occasion to make a distinction between Passive Solar schemes and Passive Houses:

Passive Solar	Passive House
Specific insolation requirements	Works with minimal solar gains (e.g. southern orientation)
Additional thermal mass requirements	Does not need additional thermal mass
Needs favourable weather conditions to be comfortable	Is comfortable year round
Provides solar gains predominantly during spring and fall	No heating requirements during spring and fall
Relies on natural forces for ventilation	Uses controlled mechanical ventilation
Design principles are widely promoted	Clearly defined and proven concept

Achieving a good indoor-outdoor flow is generally desirable for a residential building. Yet, when indoors and outdoors are not sufficiently separated, it is impossible to condition the indoors efficiently. You need a lot of energy to keep the interior of a sieve in a thermal state different from its environment.
There most definitely has to be an air exchange between inside and outside, and this really is a matter of survival. However: it is nearly impossible to construct a house with involuntary openings, i.e. air gaps in just the right way to provide optimum ventilation regardless of outdoor conditions. Thus, while they are not airtight, average houses are usually not at all well ventilated. Humidity and insufficient oxygen supply are a result. And this is where the circle closes: a precondition for efficient ventilation is reliable airtightness of the building envelope. Without it, airways and ventilation effects are uncontrollable.
Nothing prevents you from opening windows and doors in an airtight building. It’s just: only in an airtight building can you use windows and doors – or an efficient heat recovery ventilation system, to control in- and exfiltration. The added bonus is that noise and six legged friends will be bared from entering as well – unless you open a door or window for them!

When designing highly energy efficient buildings, every last bit of performance counts. R-values as customary given in NZ are unsuitable to provide detailed information about the thermal performance of an insulation layer in this regard. R-values are usually derived values: nominal thickness of the layer (in m), divided by thermal conductivity of the specific material (in W/(m K)). The result of this calculation is – according to International Standard 6946 - expressed with at least 3 digits after the dot, but this is reduced to only one digit in NZ product ratings.
Let’s say for insulation layer A, the calculatory R-value is: 0.950 m²K/W, and for insulation layer B: 1.049 m²K/W – under rounding rules, both get an R-value rating of 1.0 (usually, no unit is given in publications when R-values are mentioned in NZ).
With the same rating, there is a difference in performance of 9.9% – let’s do some rounding ourselves here and make that 10%.
With just the R-value stated, this uncertainty is concealed from the consumer. While the uncertainty margin shrinks with growing R-values, it still remains totally unclear, why essential values are not stated, and a broad brush approach is taken instead.
Countries that do take energy efficiency in the building sector seriously, i.e. all of Europe, including the UK, do not use R-values as the measure of thermal performance, but use thermal conductivity as a clear and unambiguous indicator. If the thermal conductivity and layer thickness for a product is known, the R-value can easily be established by simple division – due to rounding, however, this doesn’t work the other way around. For loose fill insulation products, R-values are impractical in any case, as the layers thickness will conform to e.g. an existing cavity - not any arbitrary thickness stated on the product's documentation. But even with blanket type products: if product A has a thickness of 8 cm, with an R-value of 2.0, and product B a thickness of 86 mm, with an R-value of 2.1 - it isn't easy to figure out the better of the two!
Thermal conductivity is given with 3 digits after the dot, which makes it very easy to compare performance of products (e.g. mineral wool might come in a range of 0.032-0.045 W/(m K)). At one glance it is obvious, which is the product with the best thermal performance.
The thermal conductivity of materials is not easily obtainable in NZ, yet many a little matters, when thresholds need to be met. To build better buildings, better information is an essential precondition, which makes all the difference between planning and guessing. Especially with Passive Houses, there is no half way. Either you are comfortable without a heating system – or you are not. There is no room here for large margins of uncertainty, in particular if they are easily preventable. To all manufacturers of insulation material: show us your thermal conductivities!

While you do not need a fireplace in a Passive House to keep warm, sometimes even building physicists like to be romantic and gaze at a flame. So, if you don’t mind the extra money, why not install a fireplace in your Passive House? Of course you need a clean, highly efficient system, but that is not enough.
To operate a fireplace safely in a Passive House, 4 conditions must be met:
1. The fireplace must be ventilated independently (external air supply)
2. The whole system (fireplace/flues) must be airtight
3. A flap valve in the flue must prevent back drafts
4. A differential pressure switch must switch off the ventilation system, if large pressure differentials exist (in case of a malfunction).
Without these safeguards in place, there is a risk of suffocation when fires are operated in conjunction with a ventilation system.

Check here for an example that meets condition 1 and 2 (sorry, German only):