Ulster Unionist MLA Roy Beggs had asked Mrs Foster to update the assembly on Social Investment Fund (SIF) projects.
He said constituents were in "urgent need" but none of the £1.8m allocated for fuel poverty had reached them.
Mrs Foster said the SIF was making a "huge impact" on people's lives and the UUP should "get with the programme".
"The first thing I would advise the member to do is calm down," the first minister told the Northern Ireland Assembly.
She added: "I am really, really disappointed to hear that the Ulster Unionists still haven't got what is actually happening in their own constituencies.
"What is actually happening is that we are making a real impact on constituents."
Ms Foster said the funding was helping with employment programmes and making a difference in areas "right across Northern Ireland".
Mr Beggs, a UUP MLA for East Antrim, said the SIF was first proposed six years ago and he criticised delays in implementing the programme.
He claimed it was "an indictment that, at this date and time, none of the £1.8m allocated to tackle fuel poverty has reached any of my constituents who are in urgent need".
Mrs Foster replied that a total of £80m was going to be spent on SIF projects.
"Hopefully by the time it is implemented, the members in the official opposition - that is the Ulster Unionist Party because they have deemed themselves to be the official opposition - will get with the programme," she said.
The SIF fund was set up in March 2011 to tackle inequality and unemployment.
In October 2013, a question from UKIP's leader in Northern Ireland, David McNarry, revealed that none of the £80m had been allocated but almost £400,000 of the fund had been spent on consultants.
The following year, the then First Minister Peter Robinson and Deputy First Minister Martin McGuinness announced that £33m had been allocated to more than 20 projects.
Northern Ireland's First Minister Arlene Foster has told an MLA to "calm down" after he asked her a question about funding to relieve fuel poverty.