Furnace Sizing: Make Sure Your Installer Gets It RightAccurate sizing of any new appliance is important. Getting it right ensures safe operation, a long service life and efficient use of fuel. Here in Indianapolis, we average 116 days per year when the minimum temperature’s below freezing, so when talking about furnace sizing, make sure your installer gets it right.

Terminology. Furnace size is typically expressed in British Thermal Units (BTUs), which measure the heat an appliance produces at optimal operation.

Furnace Efficiency. It’s invariably a mistake to use your old furnace’s BTU rating as a sizing guide. New furnaces typically burn less fuel than did their predecessors, while delivering the same amount of heat. Older furnaces were often only 60 percent efficient, allowing the other 40 percent of energy consumed to escape as vented exhaust gas. An energy-efficient, modern replacement will therefore require a smaller BTU rating to heat the same space.

Environment. It’s important your installer bears your home’s physical variables in mind, such as:

1. Penetrations. Cracks around windows and doors allow drafts in, and heat out. These conditions impact sizing.

2. Heat Retention. A well-insulated home, from which heat leakage is minimized, requires a smaller-size furnace than does one of the same square-footage that bleeds heat.

Venting. Because modern furnaces produce less (and often cooler) exhaust gases than obsolete equivalents, your pre-existing masonry chimney may be the wrong bore to properly vent upgraded equipment.

Results of Incorrect Sizing. Fuel consumption isn’t the only penalty of incorrect sizing. Oversized furnaces force large amounts of heated air into their target space in too short a time. Your thermostat will cycle on and off too frequently, causing increased component wear and tear. Further, the water vapor produced by combustion will cause premature rusting, resulting in more frequent breakdowns. Undersized equipment, conversely, struggles to perform, which also shortens service life.

Correct furnace sizing is imperative
. Make sure your installer gets it right by checking that he or she is current with all the latest sizing methods. All Mowery Heating, Cooling and Plumbing technicians are fully trained in accurate sizing procedures. To arrange a free consultation for your Greater Indianapolis home, please contact us today.

Our goal is to help educate our customers in Brownsburg, Indiana and surrounding areas about energy and home comfort issues (specific to HVAC systems). 

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