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You May Not Have the Correct Furnace Size: What to Look For

We recently received what we refer to as a “no heat” call. It was May so it wasn’t a desperation call, thank goodness, but still an issue. We immediately noticed something different upon arrival at the Park Ridge residence. This home had twinned furnaces that combined for a whopping 190k BTUs of heat and they were connected to a 5 ton condenser. As is our normal procedure, we ran the load calculation and determined that the homeowner only needed a single 100k BTU furnace with a 4 ton condenser. The existing system was simply way over-sized. We were able to install a single, much more efficient system, and the sheet metal was a work of art.

The problem is, this is not as uncommon as it should be. We often see furnaces that are over-sized and can only assume the previous installation was done without a full understanding of what was needed or the installer had some extra equipment to sell. There is more of a science to HVAC installations than most homeowners, and apparently some installers, understand.

Calculating the Appropriate Size HVAC Unit

When deciding the most efficient size HVAC unit, an installer needs to consider multiple factors including:

  • Square Feet: Total square feet of the space to be heated/cooled.
  • Weather Pattern: The climate and length of the area’s hot and cold seasons.
  • Manufacturer Recommendations: Consult manufacturer charts for the appropriate furnace for the space and climate.
  • Orientation: Since windows are not usually evenly distributed on all four orientations, rotating the orientation of a building design by 90 degrees can change the cooling load.incorrect vs correct furnace sizing Chicago
  • Latitude: The sun’s angle changes with the latitude and could affect the size you need.
  • Roof overhang: The roof overhang width matters, as well as the distance between the top of the window and the soffit.
  • Window Coverings: The presence or absence of any window coverings including, blinds, curtains and drapes.
  • Energy Efficient Appliances/Lighting: Appliances give off heat, especially older non energy efficient appliances. Types of lightbulbs used and the wattage can produce significant heat.
  • Mechanical Rate Ventilation: This could vary based on home’s age.
  • Occupants of a home: General rule of thumb is to calculate number of occupants equal to number of bedrooms plus one.

Experienced installers may also consider other factors like available insulation, the specific floor plan and ceiling heights. A trusted installer will not sell you a furnace larger than what you need, saying it’s “more for your money”. The fact is an over-sized furnace will cause you problems.

Issues Related to an Over-Sized Unit

An oversized furnace is no bargain. Especially when it comes to performance.  Here are some of the issues you’ll likely experience.

  • A home that is difficult to keep comfortable. When your home has an oversized furnace it can generate a lot of heat at once, creating an environment that can be too warm. In addition to some rooms heating too quickly, rooms further away from the furnace may not ever seem to get warm enough.
  • Your furnace will “short cycle” – Because a room heats up so quickly your furnace will “short cycle”, meaning it will be in a start up and shut down mode far too often. This creates furnace wear and may ultimately lead to a furnace failure.
  • This will lead to higher fuel costs.  The start up mode is the most expensive running time for your furnace. This means when it is short cycling it is using more fuel than necessary. This will lead to higher fuel costs and inefficiency.
  • An oversized furnace will wear down quicker. If your home does not have the proper furnace size, the furnace it does have will not last as long. It may be tempting to believe that an oversized furnace may not work as hard, but the opposite is actually true.

If you’ve experienced any or all of the above, it is quite possible you too, have an oversized furnace.

Contact Althoff Industries Today!

Having a professional perform a load calculation and install your furnace means your furnace will run as efficiently as possible as long as possible. When your HVAC is properly maintained, it further ensures that efficiency for years to come. Contact the professionals at Althoff Industries for an appointment today – we service all suburbs in the Greater Chicago area. We’ll make sure your system is the appropriate size for your home. If not, we’ll recommend a system that will save you money on fuel while providing a more comfortable living environment. The more you know about your HVAC system, the more you’ll understand the value Althoff Industries brings as your HVAC technician. contact Althoff industries

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