Landlords are warning of rent rises on the horizon, after the government passed a law requiring rentals to be warm, dry and well ventilated.

The Healthy Homes Act will require landlords to guarantee that any new tenancy from July 1, 2019 must be either properly insulated or contain a heating source able to make the home warm and dry. All tenancies must meet the new standards by July 1, 2024.

Andrew King, executive officer of the NZ Property Investors Federation, said landlords were concerned.

"We are fully supportive of rental property standards, but they need to be cost effective. Not just for us but for tenants who will ultimately be paying for the new regulations," he said.

He said if the requirement was for insulation to be at the standard required of new builds, that would mean most rental properties had to be topped up.

"However, the efficacy between the old and new insulation standards is actually very minimal. The old standards provided almost all the benefit that any amount of insulation can provide. Basically, there comes a point where no extra amount of insulation will have any extra benefit," King said.

"However, the cost of topping up from the old standards to the new ones is almost as much as installing completely new insulation.

"The cost of the standards will be high and unfortunately will need to be recouped through higher rental prices, with tenants unlikely to see a large improvement in their living standards."

It comes after the Property Institute warned of a "perfect storm" as rent rises after the property boom combined with government plans for capital gains taxes, ring-fenced tax losses and higher compliance costs.

"It's all leading to a perfect storm of circumstances and means we're in for big rent increases in some parts of the country over the next couple of years."

Forecaster Gareth Kiernan, of Infometrics, said there was a chance of that if investor demand dropped due to the changing market.

"Fewer investors and fewer rental properties might not be matched by fewer tenants. But if that were to be the case we would expect it to be a temporary effect, as a lack of either investors or first-home buyers should drive down house prices more sharply at the bottom end of the market.

"Eventually, those absent investors or first-home buyers will re-enter the market once prices have got low enough to attract them."

But he said, since the country had been able to avoid massive rent increases over the last few years, they seemed unlikely to happen now, when population growth was slowing and building picking up.