Question: Hi all, this is a great place I'm happy to have found this site.. I got 2 questions, I'm planning to buy an insert for my fireplace, and I'm trying to make the right decision on the size of the unit require for my house. The house is made of concrete cement (floors, ceiling, and roof not a well insulated house, I live in Montreal, Canada it gets pretty cold up here in winter.) How do I go about calculating the right insert size. Second question, which liner is better, the stainless rigid type that screws to one another or the one piece stainless flexible type. (They're both guaranteed for life) Answer: Best way to size your insert is to talk to your local dealer and to others that you know who have similar houses. Most units are rated in maximum BTU, and you can use the HearthNet sizing guide to get an idea of the heating load of your house. Follow the heat calculator link from hearth.com/what/specific.html As far as liners, you often need to use some of each, flexible and straight, in order to go from an insert or stove to a fireplace top. I personally would use rigid for most of the way if possible, since it costs less than flexible and is smoother on the inside and therefore easier to clean...it's thicker too!