OP the below is from the Revenues website re the HRI scheme and they calculate it differently from you have been told.
1.7.1. How much qualifies if I receive a grant or an insurance payment for the works?
Qualifying expenditure (over €4,405 plus VAT per property) will be reduced by three times the amount of any grant for the works.
For example -
€8,810 plus VAT (at 13.5%) of €1,190 = €10,000 was paid for external wall insulation
€2,700 was received under a
Better Energy Home Scheme grant[broken link removed]
The €10,000 will be reduced by €8,100 (€2,700 x 3)
Leaving €1,900 (€10,000 less €8,100) qualifying expenditure
This €1,900 includes VAT of €226
The tax credit can be claimed on the €1,900 less €226 = €1,674 (before VAT).
The tax credit is €1,674 x 13.5% = €225.99.