What you need to know when shopping for a new heating system.
First lets talk about a key word and acronym that is used. The most important acronym to know when shopping for a new heating system is AFUE (Annual Fuel Utilization Efficiency) which is a measure of how efficiently your furnace can utilize it’s fuel. The more efficient your furnace, the more heat you will get per unit of fuel. I like to compare this to MPG. The higher the AFUE, the more miles per gallon you will get. Heating systems are considered to be a “high efficient heat system” when the AFUE is 90% or higher. This is when the exhaust pipe or flue as it is commonly called, is PVC instead of metal. The reason the flue piping is PVC rather than metal in high efficiency heating systems is due to exhaust gas temperature. In high efficient heating systems they have a secondary heat exchanger which extracts more heat from the unit. This extraction of heat from the secondary heat exchanger is what makes the unit more energy efficient. This also reduces the exhaust temperature and caused the exhaust gas to condense. This is why high efficient furnaces are also called condensing furnaces. This process produces water as a result and therefore the furnace is vented with PVC.
Now that we have a better understanding of what AFUE is, Lets talk about other ways to increase efficiency of combustion. While the secondary heat exchanger extracts more heat from the fuel and has a more thorough combustion process making the equipment more efficient, there is another way to increase efficiency. The second way to increase efficiency is by having multiple stages of operation. You can have single stage which operates at one BTU (British Thermal Unit) output rating or one power setting, two stage operation which operates at two BTU output ratings, or the most complex and most energy efficient unit which is modulating or variable speed operation. Modulating or variable speed furnaces operate at multiple speed settings and are constantly adjusting their output to meet the demand. Although higher AFUE appliances are more expensive to purchase, they are cheaper to operate.
Know lets talk about sizing of the furnace. BTU (British Thermal Unit) is a non-SI, traditional unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Furnaces have different BTU ratings to meet various conditions. To determine the size of furnace required or the BTU rating required, a Manual J load calculation has to be performed. More about that in another article. Once the load calculation is performed and the BTU requirement is determined you can begin to properly size the furnace. Furnaces are sized for worst case scenario, so that means in the Cincinnati area furnaces are sized to 5 degree outside air. How often is it 5 degrees outside in Cincinnati? This is a rare event and therefore single stage furnaces are over sized more often than not. This is where two stage and variable speed furnaces really help. The furnace BTU output will change depending on how much heating capacity is needed at the time. Lets image its 5 degrees outside and your home requires 100,000 BTU of heat to heat the home. Do you need that large of a furnace to heat your home if its 45 degrees outside? No you do not. This is why two stage and modulating furnaces are highly recommended. A two stage 100,000 BTU furnace will operate at roughly 65,000 BTU on first stage and will ramp up to 100,000 BTU for second stage. This lower BTU output operation in first stage heating will cause the furnace to use less gas, which is more energy efficient, and also run a longer heating cycle which will filter that air more and create a more even temperature throughout the home.
If you have an all electric heating system such as a heat pump system, then your system is rated using SEER ( Seasonal Energy Efficiency Ratio ). A SEER rating is the ratio of the cooling output of an air conditioner over a typical cooling season, divided by the energy it consumed in Watt-Hours. Another heat pump rating is HSPF (Heating Seasonal Performance Factor). (HSPF) is a term used in the heating and cooling industry. HSPF is specifically used to measure the efficiency of air source heat pumps. HSPF is defined as the ratio of heat output (measured in BTUs) over the heating season to electricity used (measured in watt-hours). The higher the SEER and the higher the HSPF rating then the better the miles per gallon so to speak. Heat pumps have the same single stage, two stage and modulating operation just like the gas furnaces.
When shopping for a new heating system consult with a qualified licensed professional. Purchasing a new heating system is a large investment and you should consider energy ratings and stages of operation and find the unit that fits your needs. Keep in mind even the most expensive heating system will not operate correctly if it is not installed correctly. Choosing the right contractor to install your new system is more important that the brand of system you choose. Quality contractors only install quality brands. Remember to read their reviews and ask questions.
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