Recently have seen an intensive, worldwide research effort on buildings. Sparked by the energy cost crises, the significant matter was first on energy efficiency, but improved comfort and indoor air quality are emerging as important benefits of proper design. New technologies, from materials to computers, are performing a profound influence on the design and operation of buildings, and our understanding of buildings has been greatly increased, including the interaction between the building envelope, the HVAC equipment, and the behavior of occupants and building operators. Completing this experience into a comprehensive and modern technology on the design of heating and cooling systems has been the main goal of this new technology. We try to cover the fundamentals of HVAC analysis and design while mentioned the way toward solutions that achieve the required conditions of comfort and convenience for the lowest life cycle cost. In many, if not most, of the decisions of the HVAC engineer, the life cycle cost is dominated by energy costs. Therefore, we try to make the costumer aware of energy costs and of ways to reduce them. For instance, we highlight the effects of the part-load performance of primary and secondary systems on annual energy consumption. Making a decision is easy when for example one option has a lower first cost including purchase, installation and costs less to operate than an alternative option. But usually an item that saves operating costs requires a higher initial investment. The optimal choice de¬pends on the circumstances. There are methods and system to measure the furnace efficiency and categorized them. A primary efficiency measurement is the annual fuel utilization efficiency (AFUE) rating. AFUE is a ratio that compares annual output energy to the annual input of energy, if a quantity of gas with a known Btu value is sent to a furnace, some of that Btu value does not end up heating the space: some is lost up the vent. AFUE rating provides a measure of that. Biased on AFUE, we can categorizes furnaces into three AFUE ranges: LOW-efficiency furnace — AFUE rating of 78 % or less. Middle-efficiency furnace — AFUE rating of 78% to 84%. High-efficiency furnace — AFUE of 90% and up. Some references say that any furnace over 80% AFUE can be considered as a high efficiency furnace; others state that 90% is a minimum AFUE but what the consumer must understand is that the higher the AFUE the less fuel the furnace uses to heat the space. Less money spent by the consumer each year. For the Consumer’s, the real measure of efficiency is how much it cost to operate the unit. The consumer switching to a high-efficiency furnace helps future generations and, at the same time, saves money. It is our responsibility as a technician to understanding of AFUE. A furnace is a major investment for most homeowners. High" efficiency cost more to purchase and install. Then when we repairing the old furnace is just not cost effective. We should make the consumer aware of high-efficiency Furnaces offering an AFUE greater than 90% are available if the old furnace is in the 70% range, replacing the high-efficiency unit gives the user a long-term payback. Even for refrigeration for example we have two refrigerators, both providing the same quantity and quality of service. In any case it is clear that choosing on the basis of first costs alone is very low minded. The cheap refrigerator, would be very expensive in the long run. A logical decision takes all the costs into account that will be afford over the lifetime of the item. Or in simple word, it is based on an analysis of the life cycle cost. One would like to achieve the greatest benefit for the lowest life cycle cost. In a free market economy, purchase decisions are based on money. Therefore energy investments must be made on the basis of the monetary value of the energy, not on the basis of its physical quantity. And, of course, one must include all costs, not just the energy.