Multi-billion euro retrofitting plans for older homes will only reduce household carbon emissions by a fraction of the amount expected.
That's because householders are inclined to enjoy their new-found comfort by leaving the heat on for longer or heating rooms they previously could not afford to.
Analysis by the Department of Public Expenditure and Reform shows the reduction in energy use for home heating in such cases tends to be much less than expected.
As a result, carbon reduction may be only 30pc of what would otherwise be possible.
Analysts call it the "rebound effect" and say retrofitting of social housing shows natural gas usage falls "much less than a ratio of one to one for each incremental increase to the thermal efficiency".
They say energy use will fall but: "Because many of these households, which are lower income households, are likely to have been under-heating their homes prior to receiving upgrades, some of the savings might be taken in the form of increased comfort levels."
They continue: "Generally a 70pc discount will be applied to the projected savings figures to take account of the expected rebound effect (people choosing to heat their homes better)."
Retrofitting on a grand scale is one of the big climate action promises of all the parties going into this weekend's General Election.
Fine Gael is pledging to upgrade 500,000 homes by 2030, focusing on installing internal and external insulation, new windows and more energy efficient models of gas and oil boilers.
The €5.8bn package would begin with social housing but expand to a mix of private and publicly owned homes, covering the full cost of the former and grant-aiding the latter.
But without switching to alternative fossil-free heat sources such as heat pumps or district heating schemes that tap into the heat generated by large industrial facilities, the comfort and health benefits of retrofitting will not be matched by carbon reduction.
Fine Gael has said it also wants 400,000 heat pumps installed in existing homes by 2030. But the greater expense involved will require the roll-out of yet to be developed low cost green loans and easy-pay methods spreading the cost over many years of utility bills.
Finance Minister Paschal Donohoe acknowledged that investment in retrofitting alone would not substantially reduce carbon emissions.
"You then need to work with homeowners and tenants to encourage them to change their behaviour inside their homes so that this investment goes all the way in delivering the climate emissions change that we want," he said.
"I'm really confident that as we explain to homeowners and tenants the importance of the investment we made in their homes that we will then in turn accelerate the behavioural change in homes that allows this investment to make a real difference."
Climate Action Minister Richard Bruton said heat controls, accessible by phone, would help people avoid wiping out the benefits of insulation by unnecessarily heating homes when they were out.