A flue is the void through which smoke, fumes and gaseous discharges pass, not the pipe or structure forming the void. The pipe is referred to as a flue pipe and a chimney is that part of the structure of a building which forms a flue. For example, the space within a brick-built chimney is the flue. Most heat-producing appliances must be connected to a flue, in the form of either a chimney or a flue pipe. Unflued appliances can lead to condensation trouble, but some oil-burning and gas appliances are designed to operate without being connected to any kind of flue. Some gas appliances do not connect directly to a flue, for example, a gas cooker.
There is only one spelling for panic ; the verb is inflected 'panic, panics, panicked, and panicking’. The form panick is used for progressive tense, past tense and past participle. We don't write panick today, though English speakers from a few hundred years ago might have (in the same way they might have written musick). When the alternate spelling “panick” is used for the past participle: "I panicked last night at the disco." When it’s use for progressive tense: “Invariably, when markets are panicking, they sell the stocks quickly.” It's the rule for root words ending in "c" is that you have to add “k”, so the spelling is related with the pronunciation. If we don't add the <k>, it looks as if the <c> has to be pronounced /s/. If the "k" was not there, “panicing” would look like the word which is supposed to be pronounced as if it is ended in "sing," while “paniced” would be pronounced like “panised”. The same