why furnace takes so long to warm?

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There are several potential reasons but we have insufficient info from you to be sure. Is it colder outside compared to the condition now? Have you updated your furnace to a more efficient one? Do you have more people opening and closing exterior doors now than before? Did you do anything to your insulation? There are many other reasons as well.

You have too vague a question... Do the walls have any insulation? Is the furnace on a timer IE: off for extended period? What is the efficiency of the unit? Is it undersized? Try giving more info so maybe your question can be answered.