The government's admitted to a "significant" problem with one part of the Healthy Homes Standards, the day they come into effect.
It relates to the heating landlords have to install in apartments and new builds.
As of today, private landlords must ensure their rental properties comply with the standards within 90 days of any new tenancy.
There's been a major problem with the heating assessment - resulting in landlords buying heat pumps and heaters that are too large for the property.
The government's had two years to sort out the details, but now the responsible minister's been told there's a problem with the way properties are assessed for heating, and it should be changed.
Associate Minister for Housing (Public Housing) Poto Williams says officials have been told by the sector the assessment tool's been overstating the heating needed.
However, New Zealand Property Investors' Federation executive officer Sharon Cullwick says the problem extends beyond just apartments and new builds.
"The whole heating tool is a big issue and has been from the start.
"We've had heating experts, heating engineers, talk with government and say the heating tool requirements of the Healthy Homes are way more than you'd ever need in a property," says Cullwick.
The government is taking another look at the heating assessment, which she welcomes.
A new build is not subject to the Healthy Homes standards - until tenants move in.
Cullwick says that creates more headaches as there is no consistency between those standards and the Building Code.
"They really need to change the Building Code, then every new build is up to the Healthy Homes standard, otherwise if you buy a new build today and you're looking at putting tenants in it, you actually need to get the heating up to the requirement of the Healthy Homes."
She says many property owners who may not have needed to have already forked out.
"If they do turn around and change the heating tool and reduce the size of the heating ...i t means there'll be a lot of heat pumps, air conditioning units that would have been thrown into the dump because there's nowhere else to put them."
National's housing spokesperson Nicola Willis says it can also be problematic for tenants.
"Landlords want to make sure their tenants have warm homes and what they say is sometimes the heaters seem so big for the spaces that tenants are reluctant to turn them on at all."
It's important to get the right heating for the right space, she says, because "otherwise tenants might not use it because it's too expensive to use".
The government's already facing criticism because its own social housing stock under Kāinga Ora does not have to comply with the standards until July 2023.
Willis says every tenant should be able to live in a warm, dry home but it's "really important that the government put the standards in the right place and that it follow its own rules".
Williams however argues there is a huge portfolio of houses to upgrade and the government needs to make sure any improvements are done properly.
The Healthy Homes Standards are just one of a number of policies coming into effect today, including main benefit increases, higher paid parental leave payments, new rebates for plug-in and hybrid vehicles and the introduction of the new Migrant Exploitation Protection Visa.