Homeowners who applied for a grant to improve insulation and energy efficiency in their houses fear they will "be out of pocket" after the scheme ran out of money earlier this year.
The scheme was announced by the Department of Communications, Climate Action and Environment in 2017 to help people retrofit their homes.
Grants of up to €60,000 were available from the Sustainable Energy Authority of Ireland (SEAI).
Speaking on RTÉ's Morning Ireland, Conor Murphy said he was preparing to move home from Germany and was renovating a 1930s house.
He had applied for the Deep Retrofit grant and was confident he would get it as his building contractor had never been refused before by the SEAI.
Mr Murphy said his contractor told him that the SEAI said all funding had been suspended and that any applications that were submitted were not going to be processed this year.
The contractor said he had more than 40 homes that were going to be affected.
The SEAI told RTÉ News that no work should commence until a formal letter of the grant had been offered.
Mr Murphy said they had already started renovations because it was work that needed to be done on the house.
He said: "Two things, so the SEAI, to get the grant you actually have to have the work completed by October, that's six weeks from now.
"So in order to get builders on site and everything arranged, we needed to start anyway in advance.
"Then the second thing was, as we were working on the renovations and became aware of the grant and we talked to our main contractor and he said that they'd never been rejected, they were very confident that everyone was getting the grant.
"So we increased our budget to invest more into the house in terms of the grant options that were available, in terms of like solar panels, in terms of insulation, we went to a higher level than we would have in the expectation that we could have actually gotten the grant."
Mr Murphy said it was like a "Catch 22", that they had to apply for the grant, but they could not do the work before October, so this was why they were pushing to find out where they were in the process.
He said that after spending thousands of euro preparing for the grant, he has found out he will not get it.
Mr Murphy said he will be around €50,000 out of pocket because they increased their budget on the expectation of getting the grant.
He said the work would upgrade their house from BRF level to BRA level because they thought it was a great initiative from the Government to support or better climate change and more energy efficiency in the home.
Mr Murphy added he would not have been able to invest that much on his own without the grant.
RTÉ News requested an interview with the Department of Communications, Climate Action and Environment, which announced and funded the pilot, but no one was available.
A spokesperson said it was an SEAI-administered scheme.
Tom Halpin, Head of Communications with the SEAI, said the Deep Pilot scheme had a total budget of €21m.
He said that money was committed earlier in the year, but there would always be some degree of fallout where projects that had been grant offered would not proceed, so he said it was never possible to say that the money was 100% committed.
Mr Halpin said it became apparent in the second quarter of this year that they were likely to exceed the level of budget available, and therefore may not have been able to commit to all of the projects.
"We entered into discussions with our primary stakeholder, our Department of Communications, to understand what options might exist because we were keen not to disappoint homeowners that were part of applications on the understanding, we were working on the basis that the applications that we had were not going to be proceeding with works.
"But we also needed to make sure that we didn't disappoint people if there was opportunities for extending the funding, or opportunities indeed for holding these applications for what might be a future follow on programme. So it was never going to be 100% cut and dry."
Mr Halpin said the applications had a very slow start, but towards the time they closed applications they had risen to exponential rates.
He also said contractors were aware of the conditions that no work should commence [before the grant was confirmed], so they would not have been aware that people were putting themselves in any form of financial exposure.
Mr Halpin said an application that had not received an offer was under strict guidance not to proceed.
In response to why the SEAI did not notify people in March or April that the funding had run out when the closing date was in July, he said it was well communicated that the pilot was not a time-bound process as such.
The SEAI expected it might run from two to three years, but the purpose of the pilot was to get a portfolio of suitable properties for future programmes.
Mr Halpin said the SEAI kept accepting applications because it is not a sequential application process.
He said it thought there may be options for follow on funding for some applicants who do not meet the criteria.
Mr Halpin added it was always a pilot programme intended to help develop the evidence for a longer-term programme - to gather the evidence to fill a portfolio, then close the pilot and review all the evidence.
Mr Halpin "that is absolutely the case" in relation to people who have received a grant offer letter, that they will receive their money.
"Those letters of offer are 100% solid, some people have gotten letters of offer last year, some have got letters of offer this year and those will be honoured and the amounts will be paid in accordance with the grant agreement that the contractor entered into.
"Absolutely (the money is there to pay them) this is a well-governed scheme in that regard."
The decision to suspend the SEAI grant is penny wise and pound foolish, according to a Green Party MEP.
Speaking on RTÉ's News at One, Ciarán Cuffee, said the decision is "bitterly disappointing" both to the householders who had applied for the funding and to contractors whose businesses were geared towards providing the necessary work.
The Dublin MEP said commitments were given to the hundreds of people who had applied for the grant and there was an expectation that the scheme would continue for a number of years.
Mr Cuffe said the Taoiseach, Leo Varadkar, has said Ireland would be a leader on climate action but this represents a step in the opposite direction.
He said the Government has "pulled the plug" on what was turning out to be a "very popular and successful scheme".
"This should be the time when we are rolling out more grants rather than rolling back on what we already have," he said.
Mr Cuffe also said there were questions over when the Government knew there were funding issues with the scheme.