Hi Tony - the feed-in tariff is for generating electricity and so is payable on solar pv, wind turbines, micro CHP and micro hydro. The domestic RHI is for generating heat and is payable on heat pumps, biomass boilers, wood pellet stoves with a back boiler and solar thermal. They are two totally separate subsidies with different purposes, and are very unlikely to be amalgamated.

You are right that the RHI payments will be made over seven years. However, the calculation of the incentive has been made over 20 years, and condensed to make it more attractive to homeowners who have a tendancy to move on average every 7 years or so.

Unlike the feed-in tariff the RHI is not designed to give a return on investment, but to level out the cost differences (up front and running costs) between existing fossil fuel heating and renewables. We've got a detailed Q&A blog on YouGen if you want to know more http://www.yougen.co.uk/blog-entry/2010/Domestic+renewable+heat+incentive'3A+your+questions+answered/