We have a two story house (in Nelson), with an open stairwell between the two levels. We were told that a ventilation system that circulated between the two levels would be very-difficult (expensive) to retrofit in our house.
They suggested a ceiling fan in the stairwell to push warn air down in winter or reversed pull cool air up in summer.
Years ago, one of the ventilation companies was selling individual room ventilation units that incorporated heat recovery. They were installed in the wall close to ceiling height. I was looking at them for a house I moved out of in 2007.
Sounds like our house.
I've got an appointment with SmartVent, they seem to cover a lot of the options we are considering, hopefully they aren't pushy and revolting like HRV
We used Smartvent in our previous house in Nelson. We were very happy with the service, product and performance.