Which furnace should I get?
Before answering this question, we want you to know that Great Degrees will work for you to ensure that the furnace model selected for your application:
- meets your needs and expectations,
- provides quality comfort,
- is properly sized,
- is properly installed, and
- is reliable.
There are three main items to consider when choosing a furnace today. They are combustion efficiency, burner staging, and blower motor type. All of these items are discussed in the sections which follow. By understanding the different choices which can be made in each category, you will be able to select a furnace that appeals to you. Great Degrees will analyze your current system's performance and air distribution system (if applicable) and other specific details of your application. We will then perform a heating load calculation to ensure what you like is in fact appropriate and is sized to the specific needs of your application.
High-Efficiency Condensing or Mid-Efficiency Non-Condensing?
Condensing furnaces retrieve the latent heat contained in byproducts of combustion by cooling those byproducts below the dew point. This extra heat extraction results in condensation of water vapor in those byproducts. Because water vapor is condensed into a liquid, condensing furnaces require a drain, and they also vent to the outdoors through PVC vent pipe, instead of through a metal or masonry chimney as is typically used for lower or mid-efficiency furnaces. Because condensing furnaces are more sophisticated and require different venting and a drain, replacing your old non-condensing furnace with a condensing furnace costs a bit more than replacing it with a simlilarly equipped mid-efficiency non-condensing furnace. However, with current tax credits, if you qualify, the net installed cost ends up being about the same as you would pay for a similar lower efficiency furnace. Also, you will save a minimum of 16% on natural gas costs versus your old non-condensing furnace with a new 95% efficient condensing furnace. Many people save 20% or more, particularly if installing a high-efficiency condensing furnace with multistage burner and / or variable speed blower motor features. Due to constraints, a high efficiency condensing furnace may not be appropriate for you or your particular application. Mid-efficiency (80% efficient) furnaces are a good alternative under such conditions. These furnaces are non-condensing. They do not require a drain, and if you have another non-condensing furnace now, they typically vent the same way as your old furnce, although a chimney liner may be required if venting into an existing masonry chimney. All modern residential gas furnaces are equipped with a draft assist motor. These motors help draw the products of combustion through the furnace's heat exchanger and send them out into the external vent system. Natural draft furnaces without such a motor are a thing of the past.
Single-Stage or Multistage Burner?
Typical furnaces have single-stage burners. These burners are either on or off. More sophisticated furnaces have multistage burners. Instead of being either on or off, multistage burners are able to vary their heat output to more closely match the load created by the outdoor conditions. The result is more even comfort in heating mode, because such multistage furnaces run more continuously on a lower fire setting when compared to a single-stage furnace of the same total heating capability. In addition to ensuring more even comfort, less starting and stopping is associated with multistage furnaces. The net result is that multistage furances experience less wear and tear on their components, and they provide better overall efficiency. Multistage burners are available that fire at two or more discrete levels of output, as well as models that are completely modulating. Furnaces with more stages or which completely modulate provide the most even comfort.
Multispeed or Variable Speed Blower?
Multispeed blowers are older technology. They start up quickly. Variable speed blowers ramp up to speed slowly, and they also ramp down slowly when turning off. As such they are much quieter than multispeed blowers which instantly start at full speed. Multispeed motors typically have three or four speed taps (wire leads), two of which are used for your particular application (one speed for heating and one speed for air conditioning; the remaining speeds go unused). Variable speed motors also use somewhat less electricity than multispeed blowers. Depending on how you run the blower, the savings will be more or less. If you run your blower continuously, and if you do not need it to run on high speed continuously, then the variable speed blower will provide more savings when compared to a multispeed motor not capable of running as such low speeds, and as such, is forced to run at a higher speed to provide continuous circulation of the air. Variable speed blowers cost a bit more than multispeed blowers, but the quieter starting and stopping, along with the energy savings is worth it to many people. If you are contemplating installing an entirely new system for a home, complete with air distribution system (duct work), then if you plan to zone the ducts with dampers, a variable speed blower will propably do a better job for you than a multispeed motor. Within certain limits, variable speed motors will deliver the same amount of air flow as static pressure varies. This means your equipment's efficiency will not vary as dampers open and close when compared to similar equipment operating with a multispeed blower. Air flow through multispeed blowers varies as dampers open and close. This can result in more adverse impact on comfort and efficiency when the multispeed blower is used instead of a variable speed blower in a system with zoning dampers.
Summing Up
Features within any one category above are mutually exclusive. That is, you cannot get a furnace with both a multispeed blower and a variable speed blower, nor can you get a furnace which is both condensing and non-condensing. However, between the categories, furnaces are available with all combinations of features. For example, you can get a high efficiency condensing furnace with two-stage burner and variable speed blower motor. Or you can get a mid-efficiency furnace with single-stage burner and variable speed blower. Choose the combination of features which you feel is best for you.
