The Taoiseach has insisted the Government is "not against" putting HEPA air filters into classrooms.
However, Micheál Martin says they may not be needed in every classroom - and suggested Government data questions the real-world application of such filters.
Opposition parties and a number of public health experts have called for the HEPA (high-efficiency particulate air) filters in order to reduce COVID-19 transmission in schools.
The Independent Scientific Advocacy Group (ISAG) has argued it's one of the measures needed to stop case numbers rising.
They say the Government should set "scientifically-informed air hygiene standards for indoor settings, suitable for an airborne pandemic virus".
Professor Luke O'Neill, meanwhile, says the filters aren't particularly expensive, and having them in every classroom would be "yet another weapon" to use against COVID.
Sinn Féin leader Mary Lou McDonald raised the issue during leaders' questions in the Dáil this afternoon.
She called for the Government to roll out the filters to all classrooms, saying it's now clear they have an important role to play.
She said teachers and students in classrooms have been "wearing hats and scarves, with windows wide open" under current ventilation guidelines.
Deputy McDonald said the Government's approach to ventilation has been simply to advise schools to keep windows open.
People Before Profit's Richard Boyd Barrett also highlight the issue, saying putting filters in every classroom would cost "a fraction of the money the Government is having to pour out on income supports".
Micheál Martin insisted the filters will be provided in certain situations.
Martin says the public health advice has been fresh air (through windows being open) is the way to go
Says schools can buy HEPA filters if they wish
— Seán Defoe (@SeanDefoe) December 7, 2021
He said: "We're not against HEPA filters - we're for, and will provide resources for them. I've said this three times today already.
"There are 50,000 classrooms across the country, between primary and post-primary schools. The Department and the minister are adopting a targeted approach."
Mr Martin insisted the Education Minister has "at all times" adhered to expert advice around ventilation.
He argued that fresh air is the most effective form of ventilation, but officials have provided "very substantial resources" to schools to buy HEPA filters where needed.