Burning smokeless coal in household stoves is a major source of air pollution despite its apparent clean credentials.
There is little difference between smokeless and smoky coal and the pollution is worsened when firelighters are used, the University College Dublin study found.
The finding is worrying for many thousands of householders who converted open fires to stoves or installed free-standing models over the last 20 years because they were believed to be more energy efficient and cleaner.
Scientists found that burning just 2-3kg of coal, briquettes, peat sods or wood produced the same amount of particulate matter (PM) as driving a typical, modern diesel car for several thousand kilometres.
PM such as soot, smoke and other dirt is the main cause of premature deaths from air pollution here.
Around 1,200 people die prematurely from air pollution in Ireland each year while many others suffer a worsening of chronic respiratory conditions.
The scientists say smoky coal bans "while laudable in principle" are ineffective and that all solid fuels in urban areas should be discouraged instead.
Solid fuels provide 20-25pc of home heating and while their use has been slowly decreasing, the proportion burned in stoves has increased.
Sod peat, bituminous coal and smokeless fuels each account for about 30pc of the solid fuels used while the remainder is mainly wood.
In the Environmental Protection Agency-backed study, Dr William Smith and Dr Cian Quinn concluded: "All solid fuels tested, including fuels categorised as 'smokeless' under Irish law, were found to generate very substantial levels of particulate emissions.
"Combustion of just two to three kilogrammes of any of these fuels produced a mass of particulate matter equivalent to driving a typical, modern diesel car for several thousand kilometres. Firelighters contribute a disproportionately high fraction of PM emissions, relative to their energy content and mass.
"Because those emissions are generated in residential areas, they have the potential to impact appreciably on human health.
"The combustion of solid fuels in manually operated, domestic-scale appliances should therefore be discouraged in urban areas. Mandating the use of so-called smokeless fuels, while laudable in principle, is unlikely to reduce particulate emissions to an acceptable level."
They said emission standards should be set for firelighters and moisture standards for wood as wet wood was worse.
They also said if stoves were to continue in use, they should have electronically controlled air inlets to improve efficiency.
It is the second study in recent weeks to cast doubt on the efficacy of the smoky coal ban that is being extended to all towns with populations over 10,000 from September.
Research by scientists at University College Cork showed that in three towns, Killarney, Enniscorthy and Birr, where solid fuel use is high for home-heating, all had air pollution problems over the winter.
That study questioned the impact of banning smokeless coal from the towns if the use of peat and wood were not tackled too.
The Programme for Government pledges to move towards a full nationwide ban on smoky coal.
It also promises to retrofit 500,000 homes with an emphasis on moving away from solid fuel use by 2030.