I have a very bad problem with dampness and condensation. My double glazed windows get really misty and water builds up on inside of them and then collects on window sills. Every time I put new sealant on it soon becomes covered in black mould. I was tempted to buy new double glazing as I think the windows I have are not up to standard. But other people tell me that it isn't the windows that are the problem it's comingfrom withinthe house. I bought a dehumidifier last year which works upstairs with limited success. Any ideas? I have a blocked up fireplace and chimney with no ventilation. Would this be a factor if so what u recommend for ventilation in living room and bedroom where chimney runs? Look forward to some ides ty