The Green Homes Grant can be used in conjunction with the domestic Renewable Heat Incentive (RHI), but only if you do not currently receive RHI payments for the specific installation you are applying for with the grant.
Homeowners will first need to apply for a Green Homes Grant and then apply for RHI.
The cost of the vouchers provided will then be taken off the value of their projected RHI payments.
However, this cannot work the other way round: you cannot apply for RHI first before applying for the Green Homes Grant.