Over 10,000 gas boilers are believed to have been installed illegally last year.
The Consumer Association of Ireland recently surveyed the sales of gas boilers in Ireland in 2011.
It found that 27,500 units were sold last year, however, just 17,400 were registered by officially certified installers.
The Consumer Association of Ireland said it understands the financial pressures on households.
But it's Chief Executive Dermott Jewell said that it is a dangerous option: