We live in a 160 year old converted school house, that unfortunately suffered through the autumn and winter every year with significant condensation on all windows, frames and doors, resulting in black mold, everyday during these periods we were checking all windows, emptying dehumidifiers, wiping windows and spraying chemicals to keep black mold away, we then saw the environment TV advert and thought it was exactly describing our problem, so decided to get a quote, which was quite expensive, but we decided to proceed due to the money back guarantee being offered, installation took place (quick, painless and tidy) then literally next day we could see a major difference and thought it could be a fluke, so checked the next day and the next, through snow outside and normal winter weather and all our windows, sills, doors are all condensation free, black mold has gone completely, we are so delighted that we decided to go with envirovent and would recommend to others with similar issues if cost allows - we hoped this would "help" but actually totally stopped the problem and more than met our expectations