I have a warm air heating system in the house I rent out. I lived there for 26 years and I am aware that it is not as efficient as a wet system. We had additional electric heating for times when it was very cold. My new tenant is requesting we put in a wet system as she cant afford to use the electric heaters. I have full sympathy with them over this but dont feel I can do more than I have done by offering to pay for additional heaters which she has so far refused.
You are or the tenant can claim on the grant which may pay 100% or at least 75% for the new heating system. Also the old grant for new boilers is still active too.