Whats the difference between a Heat Pump and Positive Pressure Ventilation system?

Well the simple answer is ;

A heat pump is basically a air-con unit that can heat your home efficiently (up to 3-4 times more efficient than conventional heaters).

A Positive Pressure system draws fresh, drier air from the roof space or from outside and passes it through a filter before gently distributing it around the home via diffusers set in the ceiling.

Heat Pumps;
How it works.
In NZ, ductless heat pumps (also known as “mini split” heat pumps) are the most common types of heat pump units.
They offer better quality air conditioning than ordinary air conditioners.
Ductless heat pump uses technology similar to that of a refrigerator.
This type of heat pumps is chiefly used for heating however this can also serve as a cooling unit for your home.
The best benefit of having ductless heat pumps is its energy efficiency compared with normal electric heaters.
An extra benefit of ductless heat pumps is its versatility and flexibility in interior designing. A lot of variations and designs are available such as floor stand types, those that can be suspended over ceilings or walls,
Ductless heat pumps are equipped with options for indoor handling of air which allows you to adjust the heating and cooling thermostats for your own needs.  Installation of these units takes a little amount of time with less damage to your interior designs.

Installation of ductless heat pumps should be properly done by an appropriate person. .

The price range for these units starts from $2800, prices also vary depending on configuration and zones found in each unit. When purchasing ductless heat pumps you should opt for units with warranty; warranty varies with each manufacturer so be sure to check and ask for it.
There are also DIY systems available from Bunnings of you want to tackle the job yourself.

Positive Pressure Airflow systems;
How it works
In with the good, out with the bad.
This process positively pressurises your home, forcing out moist stale air through gaps in windows and doors or through special exhaust vents.
Continually cycling your home with fresh, dry air removes air borne toxins, harmful pollutants, dust and dust mites.
A filtration unit traps pollens, dust and allergens.
This filtered air is distributed into each room ducting.
Moist air is forced out around windows and doors, making your home drier, which makes it is easier to heat.

A professionally installed unit starts at around $2000 or you can check out the DIY Smart Vent units at Bunnings if you are game.

Conclusion

In my opinion you need both units to have a healthy efficient home.

However I started with a cost effective Smart Ventilation system as it costs only 20 cents a day  to run the fan and can be totally automated or have a control unit if you like.
The Heat pump is probably the best heating option available to New Zealanders at the moment.