I am going to replace a single-glazed glass rooflight over the hall with a velux window. I want to keep the light coming in, but want much better heat insulation as the hall is a very large space. The glazing options I have seem to be double-glazed or triple-glazed with varying U-values – 0.89, 1.0, 1.2 and 1.3. I want to reduce my heating bills if possible, but the main reason is to make my flat feel warmer. Is it worth paying for a better U-value, or would a slightly worse U-value make only a negligible difference?
I currently have condensation problems with the current window. The velux window comes with a ventilation bar with dust and insect filter. The window will be in an inaccessible place, so is it worth leaving the ventilation bar permanently open or will this negate the heat insulation from the double/triple glazing. If I leave the ventilation bar closed, will this cause condensation?
Thanks in advance for any advice!