Last edited: 13 Jul 2018 Fizzy, Leo, thank you both. Mods, please start a new thread if you think it's best. I need to make a decision about this. We live in a 10 y.o. apartment (Celtic tiger). During last winter I recorded temps of 12-13 C in the bedrooms. There are convector heaters in them (plus a small storage heater in the corridor and a large one in the living room/kitchen). When the kids were staying with me I had the heaters on the timer for at least 20 min of every hour during the night! I tried the same with an oil heater but it made an awful noise every time it turned off and kept waking up the kids. Both gave off a funny smell and with the convector heaters the room was cold very quickly after turning off. The apartment is a top floor of about 90 sqm, 3 beds, dual aspect (E-W) sandwiched between two others plus one below. The bedrooms are only used for sleeping at the moment. Two have large windows, the main a floor-to-ceiling with a door on to a balcony. One of the small bedrooms has an air vent (whole in the wall, which I partially blocked because it felt like an arctic blizzard near it). I will be putting thick curtains on all but I don't think that will solve the issue. I'm considering several possibilities for the bedrooms: 1. Lucht type heaters 2. Small storage heaters 3. Internal insulation I'm working on a list of pros and cons of each. In the meantime, I'd welcome suggestions and ideas, also a recommendation for an expert builder or engineer to come and assess the situation. Edit: I should have added that during the week we're never in the apartment between 8:30-18:30, sometimes even less.