Andrew Little says it'll only be "greedy landlords" who hike rents on the back of his proposed Bill to insulate and warm homes.

The Labour leader's Healthy Homes Guarantees Bill is set to be introduced to the House tomorrow which would make sure all rental homes in New Zealand are warm and dry, including a requirement for a heating source in every property.

A similar Labour Bill which would have done a similar thing was scuppered by National last year after a vote was tied at 60-60.

At the time, the Government called the Bill which would have including inspecting every home "extreme".

There are now 121 MPs in the House and Mr Little has written to all of those outside his party asking them to support the proposed legislation.

"Wouldn't it be great if we had 121 votes in support of doing the right thing for our kids and families in rental accommodation?

"In the end, this is about the right standards for the right things and helping our kids and their families not get sick," he says.

The Bill would require any new leases 12 months after the law comes into effect to meet the standards, but landlords will have up to five years to meet requirements for leases which continue through that time.

Prime Minister John Key was concerned rents would go up as a result of the legislation.

"Even if they were to put a heat pump in, the question is 'would someone actually use that?' The answer is they might or might not depending on their financial circumstances."

He says the Government is trying to provide a warmer and better environment for people but won't have the cost passed on to the cost of tenancies.

"That's why we're in favour of insulation, operating smoke alarms, we think the issue of heat pumps is one step too far in private rentals."

But Mr Little rejected suggestions the new requirements would lead to an increase in rents, saying landlords will have plenty of time to absorb the cost.

"That in my view, is a cost landlords will be able to bear over that time, given the increasing value the property will enjoy over that period.

"This does not need to lead to hikes in rents, and only greedy landlords will be seeking to hike rents for this reason."

The catalyst for the proposed legislation was in part the death of toddler Emma-Lita Bourne who a coroner ruled had died partly as a result of the unhealthy state house she was living in.

Newshub.