Firstly wanted to preface this by saying that I have spent quite a while looking through all the great previous discussion around the various options to achieve effective home ventilation and really appreciate everyones input.

We live in a 1960's weatherboard house with leaky single glazed wooden joinery. We have ceiling and underfloor insulation and are planning on replacing the existing joinery with new double glazed units in the next couple of years.

The internal relative humidity level in the house ranges between 60-80% at 18deg depending on which room we are measuing in (we live in Auckland), we have a little bit of mould on some curtains in one of the bedrooms and obviously condensation problems which are to be expected with the single glazed joinery.

The house has a Simx HeatTrans system installed with a single inlet in the lounge (fed by the heat pump) and outlets in each of the three bedrooms. We literally never use this system as we set the heat pump to 19deg in the lounge and don't generate enough excess heat as we would if we had a log burner for example.

I wanted to investigate whether we could convert the existing heat transfer system into a SmartVent ventilation system as I understand a lot of the components are very similar (we already have the outlets in each room and insulated ducting running from the inlet to each of them as well as a fan). I figured we if we converted it to a ventilation system at least we would get some benefit from it rather than the system just sitting there serving no purpose! We have loose fill insulation in the ceiling and it is fairly dusty up there so I would prefer to pull air in from outside instead of the roof space. The obvious downside of this is that the outside air will cool down the rooms a lot (although it would achive the desired reduction in humidity).

Due to this, I was interested in a balanced heat recovery type system like the SmartVent Synergy system. I called up SmartVent today and had a chat with who I assume was a sales type person there who said that they very strongly advise against a balanced ventilation system in a house built prior to 2006 and that it "would not work, even on a renovated house as it still won't be sealed enough". Now I can understand that it would definitely work better in a modern sealed house, but surely it is still better to recover 70-90% of the energy from the stale air as it exits rather than pulling in cold air directly from outside, even in a house that isn't fully sealed? Does anyone have any recommendations or any other comments?

Thanks!