Northland landlords are lagging behind homeowners in taking up a Government offer of free or cheap home insulation.
Almost 1200 owner-occupied properties have been insulated in Whangarei and the Far North since the scheme began, compared with less than 600 rental properties.
The Green Party says the figures obtained by the Northern Advocate confirm fears the publicly subsidised scheme would fail those who needed it the most.
Healthy Homes Tai Tokerau spokeswoman Mel Peters agreed more insulated rental homes should be a goal for the Warm Up New Zealand: Healthy Homes initiative.
"We can't forget there are more and more people renting these days and we need to make sure they know, and encourage landlords to insulate."
Ms Peters said people she had spoken to about the initiative were in favour of it.
"We interviewed a lady last week who said it should be compulsory."
Nationwide, only a third of the 36,000 homes retrofitted with insulation since the Warm Up New Zealand: Healthy Homes initiative kicked off in September 2013 were rentals.
It is estimated more than half of properties needing insulation are rentals.
Under the initiative, homeowners or tenants are eligible for free or reduced cost insulation if they have a Community Services Card and the house is occupied by someone under 17 years or over 65 years.
In some regions, people at risk from illness linked to cold, damp housing are also eligible.
Green Party co-leader Metiria Turei said the party predicted the scheme would fail renters and this has been proven true.
"Landlords who are only interested in their immediate profit have no incentive to be good landlords."
She said a warrant of fitness scheme is needed to set a minimum standard for housing and hold landlords to account.
However, the Energy Efficiency and Conservation Authority (EECA) said the initiative should already appeal to landlords.
"Getting rental properties insulated through Warm Up New Zealand: Healthy Homes is a no-brainer for landlords," said chief executive Mike Underhill.
"Landlords will end up with a higher quality property and tenants are more likely to stay longer in houses that are warmer and more comfortable."