We have moved into new house with a big conservatory, but it's cold! It's got the plastic roof, there are companies on the Internet that can make the roof warmer has anyone tried them? Or could you change the plastic for glass? Any ideas welcome, we want to use it over Christmas )
I don't know. I've been obsessively trying to figure this out myself! We are going to put in underfloor heating - probably this (as someone on MN helpfully linked to on my recent thread).
However, this isn't really going to do it properly. I am thinking of also having a radiator put in AND getting the roof either tiled with those plastic tiles or the solar reflecting film put on. Even then it is going to be a beast to keep a normal temperature, but we really need the living space!
I have a digital thermostatic plug and an electric heater in mine, because I use the place as a plant room (I guess as conservatories were originally). Said plants are mostly tropical, like birds of paradise and bougainvillea and orchids so I need an even temperature in winter. Roof is double-walled polycarbonate (quite efficient an insulator) and the rest is double-glazing. No brick walls (which would help with heating, but previous owners didn't think of that!)
Electric heaters are notoriously hopeless at keeping a level temperature which is why I bought the plug. It keeps the temp to within a degree of that set, so I leave the heater on max all the time and let the plug just switch it on or off. Works very well.
It was -18C here last winter and it was still OK in the cons. Good job - we use it as a breakfast and dining room!