I think that if you are going for the heating part of it they will come to your home and assess your insulation first, you have to have both ceiling and underfloor insulation.
The max grant for clean heating is $500.
There are a few other criteria etc as well and a full list of providers on the website
Have a look at www.eeca.govt.nz
ETA - There tends to be a pretty long waiting list to get seen about it all too so I'd get onto it fairly smartly if at all possible
Edited by MamaT