As you embark on the journey of purchasing a new furnace for your home, you will quickly find that it is a challenging endeavor. Not only do you have the option of purchasing various brands, numerous makes, an assortment of models, types, efficiency ratings, and technologies with each, you must determine the size that is needed for your home. This involves more than the calculation of square footage. In this guide, you will be introduced to the various factors that must be considered when determining the appropriate size for your needs.

oil furnace
By Versageek – Taken by Versageek, CC BY 2.5, Link

Why is the Size of the Furnace Important?

It is often tempting to purchase a smaller furnace in an effort to save money on the original purchase. Many will lean towards purchasing a large unit to aid in maximizing the amount of heat that is emitted throughout the home. The truth of the matter is, going too small especially in areas of cold winters, or going too large may prove to be highly detrimental.

If you purchase a furnace that is too small, you will likely discover that it runs on a continual basis. Your home will not reach a comfortable temperature. It will work hard to keep up with the temperature demands of your home. As a result of the overall increased workloads, maintenance issues will arise, energy bills will increase, and the lifespan of the appliance will be significantly shorter.

If you purchase a furnace that is too large, you will find that it cycles in an irregular manner. This will result in the formation of both hot spots and cold spots throughout your home. You will also find that it detrimentally impacts the overall efficiency of the unit and that you will have to perform maintenance on the furnace more often. Finally, the longevity of the appliance will be drastically reduced.

Does the Size of a Furnace Impact its Energy Efficiency?

One of the worst situations that arises when the wrong sized furnace is chosen is that it negatively impacts the overall efficiency of that unit. The efficiency of this type of appliance is calculated based on the normal operation of the unit. If it runs too much or in an irregular manner because it is not the proper size for a home, the associated energy efficiency rating no longer applies to the system.

This means that it will use more energy than is needed and that you will see an instant increase in your utility bill. To maximize efficiency, it has to be the right size for the residence it is attached to once installed.

How is the Size of a Furnace Measured?

There is one main fact that you must keep in mind when it comes to furnace size; that is, measurement is not a reference to the physical dimensions of the system. The size is determined by the actual heating output and the amount of sheer heat that may be generated by the system.

In most instances, the output is measured in BTUs (British Thermal Units) per hour. Large BTUs are appropriate for larger spaces and lower BTUs is appropriate for smaller spaces.

In some instances, the measurement may be in MBH. This standard measurement outlines one thousand BTUs each and every single hour. In short, a 60,000 BTU system is directly equivalent to a 60 MBH unit.

If you have any questions about the measurements associated with a furnace, you may direct them to a heating and air conditioning specialist.

What Factors Should Be Considered When Determining the Right Sized Furnace?

There are several factors that must be considered when determining what furnace size is right for your home. The following outlines these factors and offers a brief supplemental explanation of each:

  1. Square Footage – To get the best sized furnace for your home, you must factor in the total square footage of the home to be heated. This measurement will help you figure out what standard range size you should narrow your search down to when shopping.
  2. Climate – When shopping for a furnace, it is essential that you consider the winter climate where you reside. If you live in Indiana, you will require a larger furnace than if you resided in the State of Georgia because the winters are harsher in Indiana.
  3. Home Architecture – When choosing a furnace, you must consider the overall design of your home. If your home faces the South, it will get more sun. This means that in the winter, you can open up curtains and blinds and take advantage of the heat put out by the sun. This means you could install a smaller furnace than if your home faces North.
  4. Floors – How many floors do you have in your home? If you have two stories, the second will provide insulative properties to the home and reduce the amount of heat that is necessary from the furnace. This means a smaller unit will work. If you have a single-story home, your heat requirements will actually be higher. If you have walls that have a lot of insulation, smaller units will work. If you have an open layout on the floors of your home, you will require a larger furnace.
  5. Insulation – If your home is well-sealed and utilizes very thick insulation, it will be more energy efficient and will be productive at holding in heat; therefore, a small furnace will be appropriate. To be able to have the warmest home possible with the smallest furnace, be certain that the walls, the crawl space or basement, and the attic are properly insulated. This will all contribute positively to preventing the loss of heat throughout the home.
  6. The Windows and The Doors – Windows and doors are known for being major culprits when it comes to leaks and even drafts. This is especially true if you do not have energy-efficient windows and doors that lack the proper sealant. If you have a lot of doors and a lot of windows, you will need a larger furnace to compensate for the amount of heat loss that will be experienced regularly throughout the spaces. On the other hand, if you don’t have a lot of windows and doors or if these products are energy efficient, you may be able to have a smaller furnace installed in the home.
  7. Ductwork – If the ductwork throughout your home is leaky, it will increase the amount of energy demand that your home has – as a whole. This means that you will need a larger furnace. It is a good idea to inspect ductwork regularly and make necessary repairs immediately. In doing so, you are increasing the overall efficiency associated with your home and you will find that your heating and cooling systems perform optimally.
  8. Heat Sources – Do you have secondary heating sources in your home such as a fireplace or a wood stove? If you do and you use those other sources, a small furnace will likely be sufficient to your needs.
  9. Exterior Walls – If you have only a few exterior walls compared to many, you will instantly find that your heating requirements are not as high. For example, if you live in a townhouse, you may be able to utilize a small furnace and it will provide more than enough heat for your living space.
  10. AFUE – The AFUE of a furnace can have a direct impact on the size that is appropriate for your home. If you want to have 100% efficiency with a 100,000 BTUs, you would need an equal amount of AFUE. If the energy rating of a system is low, it indicates that you will need a larger furnace for your home.

Square Footage Requirements

When shopping for a furnace, a general rule of thumb is that you need as low as 30 or as high as 60 BTUs for each square foot of your home. Of course, this depends on your climate. Harsh climates should be chosen at 60 BTUs per square foot.

Warmer winters may be chosen at 30 BTUs per square foot. If you would like to learn more about this topic, you may check out the information from the organization known as the Insulation Manufacturers Association that is located in North America. You may also contact an industry professional.

Professional Sizing

If you are having difficulty deciding on the most appropriately sized furnace for your home, you may have an evaluation performed by a professional in the HVAC industry. These technicians will be able to properly calculate the overall square footage of your home and all of the factors outlined in this guide to give you a precise measurement of the BTU capacity that you require for your home. We here at Reynolds can quickly assist you with this. Additionally, we will install, maintain, and repair your unit when it becomes necessary.