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Some important things to consider when selecting your new furnace:


AFUE stands for Annual Fuel Utilitzation Efficiency, which is the number that indicates the efficiency of your furnace. If you have an 80% efficient furnace, then your furnace is utilizing 80% of the natural gas o propane that is fueling it. If your furnace is 96% efficient, then your furnace is utilizing 96%, and so on.


Gas furnaces are manufactured in various sizes. These sizes are stated in BTUs, which stands for British Thermal Units. A British Thermal Unit is the amount of energy is the amount of energy required to heat 1 lb of water from 39 degrees F to 40 degrees F.

Sizes of furnaces usually start with 40-45,000 BTU, then go up from there, 60,000, 80,000, 100,000 to 120,000 or 145,000, depending on manufacturer. Some manufacturers use the odd sizes instead of even, such as 70,000, 90,000, and 110,000.

Many older homes have furnaces that are actually too large for their homes. In the past, some people thought that “bigger is better” and would put in a larger furnace to be sure the house was warm. This practice was actually counter-productive. A furnace that is too large will not run sufficient periods of time to allow the heat to be evenly distributed throughout the home.

Newer homes have usually had their furnaces sized by a calculation called a Manual J, or Heat Gain/ Heat Loss calcution. This is a standardized way to determine how many BTUs of heating capacity your home needs. If you feel that your furnace may not be correctly sized for your home, we would be happy to do this calculaton and give you a copy of the results. It is also important to calculate the size when moving from one heat source to another. For example, if you are heating with an electric heat pump, then move to a gas furnace, we would want to do the calculation to detemine the correct size of the furnace.

Gas Valve

The gas valve regulates the amount of gas going into your furnace. There are three different types of gas valves available on furnaces.

Modulating gas valve:

This gas valve has the ability to open slowly, adjust to exactly what the furnace needs and close as needed. Of course, this is the most efficient furnace and also saves energy. The cost of furnaces with modulating gas valves are usually quite expensive.

Two-stage heat:

This gas valve has a high setting and a low setting. These furnaces help to produce a more even heat in the home, similar to the modulating gas valve. Because the furnace always comes on in the low setting, these gas valves can save energy over the single-stage gas valve. Furnaces with two-stage heat are slightly more expensive than a single stage, but we consider that extra expense well woth it when factoring in the increased comfort due to having longer run times, and energy savings,

Single-stage heat:

This describes a gas furnace that has a gas valve that is either open or closed. In many homes, this is perfectly acceptable, and all you need. This is especially true in ranch style homes that don’t have a problem with hot and cold spots.

Blower Motor

The blower motor in your furnace is used to circulate the conditioned air throughout your home. This part of the furnace operates all year long, circulating the cool air from your air conditioning in the summer, and the warm air from your furnace in the winter. It will run fastest in cooling or heat pump mode and slowest in continuous fan. There are three main types of blower motors available in today’s furnaces.

Variable Speed Blower Motor:

This is the most energy efficient and quietest of all blower motors. The variable speed blower ramps up and down as necessary, and runs on only about 25% of the electricity of a standard PSC blower motor. A variable speed blower can increase your overall cooling system performance as much as one SEER. It will keep your home at a more even temperature and helps eliminate hot and cold spots. It communicates with your furnace to meet the airflow needs of the thermostat. If you choose to put the thermostat in the “On” positon, it will run very slowly when not in the active heating or cooling modes, gently and quietly circulating the air throughout your home. This type of motor converts alternating current (A/C) into direct current (D/C), which enables the motor to run very efficiently.

ECM Blower Motor:

(This is sometimes called an X13). Just as the variable speed blower motor, the ECM has the ability to transfer alternating current (A/C) to direct current (D/C), thus operating much more efficiently and more quietly than the standard PSC blower motor. Sometimes these are labeled with different speeds (such as four-speed). This means the motor has the ability to run at four different speeds to accommodate different amounts of airflow needed by different sized systems. For example, a three ton heat pump needs to move a different amount of air than a five ton. Making this motor a four-speed makes it more universal, but will only operate in one set speed for heating and one set speed for cooling. These speeds are set by the installer, and do not change during the operation of the furnace, as does the variable speed.

PSC Blower Motor:

This is the least efficient and loudest of all the blower motors. It may be described as having multiple speeds but will only operate in one set speed for cooling mode and one set speed for heating mode, again set by the installer. This motor does not have the ability to transfer alternating current (A/C) to direct current (D/C), as it operates in AC only, and uses considerably more electricity than both the variable speed blower motors and the ECM blower motors.

Draft inducer:

The draft inducer motor is responsible for assisting the exhaust fumes created by your furnace out of your home. This works in conjunction with a pressure switch. If your draft inducer motor is going out and not getting enough of the fumes out of the flue (venting for the exhaust), the pressure switch will trip and shut down your furnace. These two items are safety features and should be taken very seriously if needed to be replaced.There are different types of draft inducers. The terming of these is similar to those of the blower motor. Just like the blower motor, you can compare the different types of inducer to the settings on your stove.

Variable-speed draft inducer:

This is the most energy efficient of all the draft inducers. Like the variable-speed blower motor, this too ramps up and down as called for by the furnace.

Two-speed draft inducer:

This is more energy efficient than the single-speed draft inducer but less efficient than the variable speed draft inducer. This would be comparable to having only a high setting and a low setting on the burner of your stove.

Single Speed Draft Inducer:

This is the least energy efficient draft inducer. This would be comparable to only having a high setting on the burner on your stove. It is either operating on high or off.

Heat Exchanger

The heat exchanger is the heart of your furnace, as it transfers the heat produced to the air to be circulated throughout your home. If your heat exchanger develops a crack, this is a very serious problem and replacement is recommended. Replacing a heat exchanger is a very costly repair, and usually happens in older furnaces. Even if the heat exchanger is under warranty, by the time the heat exchanger would crack, the labor to replace it is not covered under warranty and is very costly. This is a very expensive repair, so we definitely recommend getting a quote on replacing your furnace should you need a new heat exchanger.


While all this information may seem a bit overwhelming and confusing, Westin Air’s trained sales people have the knowledge to guide you through the process of selecting equipment that makes sense for your home. We understand that your heating and cooling system is a major expenditure and should be considered carefully in order to make a wise decision. We always provide honest, free, no pressure quotes on replacement equipment.


Contact us to set up a no obligation consultation and quote.

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