Existing regulations are also very significant. The furnace should follow the legal provisions. Otherwise it can pose some problem while in operation and will have very less resell value. The furnace which can accommodate add-on-features at a later date should be preferred. Naturally the product should exhibit the legal compliance. The two issues i. e. after sales service in the furnace and its maintenance, should be given anticipated importance. If a furnace is starving for maintenance and spares it is as good as not having that. Ease of operation is another key factor. Keep in mind that many a time the person purchasing some sort of furnace is not the only person going to handle it. So think about the operability. Unnecessary complicated operation will trigger redundancy of some of the features. My websites: heat pump prices