A log stove is likely to cost between £500 and £1000, with installation costs probably the same again. Pellet Stoves will be more - a few thousand pounds plus installation.
The price will vary according to the specification of the boiler. for an average sized house, a basic log boiler might cost about £3,000, while one with a higher standard of controls might be £6,000. A pellet-fired boiler could cost £9,000.
A more expensive log boiler will be made with more expensive steel (so has a longer expected lifespan), and will have greater control over aspects such as airflow to the combustion chamber - which means that it will operate more efficiently when starting up or winding down. At these times, a boiler without as much control over air inflow, etc, can suffer from more tar, acid and other by-products of poor combustion. These shorten the life of the boiler & flue, besides leading to a lower quality of emissions.
The flue for a biomass system wil cost around £2,000 to £2,500 - this is for the sort of properly insulated flue needed for efficient operation of a biomass boiler.
As well as the boiler itself, the total installation cost will include an insulated flue, accumulator tank, pellet hopper (where needed), pump, controls and labour. including all this, the final installation cost of a basic log boiler might be £15,000 to £18,000, a higher specification log boiler about £20,000, and a pellet boiler about £25,000.
This currently high cost can be reclaimed by installing a system under the government's Renewable Heat Incentive. This scheme gives payments back over a seven year period, to help people recoup installation cost and make a system competitive with options like oil or LPG.
Remember to factor in the ongoing purchase of fuel. Bought in bulk, log fuel should be cheaper than gas, oil or coal. Pellets also now compare well with other options - buy in bulk to get the best price.