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representation of a furnace in front of a house

If you need to replace your furnace, finding one that’s the right size for your home is extremely important. A furnace that’s too big for your home will frequently cycle and be inefficient. Conversely, one that’s too small will run continuously and never keep your home at a comfortable temperature. Here’s what you need to know about BTUs to correctly size your furnace.

BTUs explained

BTU is an acronym for a British thermal unit. It represents the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. The more BTUs a furnace has, the more area it can heat.

Other factors to consider when determining furnace size

A basic rule of thumb is that 40 to 45 BTUs can adequately heat one square foot of living space. However, it’s not that simple. Besides a home’s square footage, here are six other factors to consider. 1. Climate. Homes located in cold climates require larger furnaces than homes located in areas that experience mild winters. For example, in a cold prairie climate, a 70,000 BTU furnace would struggle to warm a 1,600 square foot home, despite the previous BTU estimate. 2. Home style and orientation. South-facing homes are naturally heated by the sun during the day and may be able to get away with a smaller furnace. Additionally, two-story homes often need smaller furnaces than similar-sized single-storey homes because the second floor acts as an insulator. However, homes with an open floor plan demand higher-BTU furnaces because there are fewer walls to hold in the heat. 3. Windows and doors. Homes with old, inefficient windows and doors need a more powerful furnace than homes with fewer or more efficient windows. 4. Insulation and ductwork. Well-sealed homes with high-quality insulation may not need as large of a furnace as poorly insulated homes. 5. Exterior walls. If you have an apartment, condo or townhouse, you can purchase a furnace with fewer BTUs than what you’d need for a stand-alone home of the same size because less heat will escape through the walls. 6. Furnace efficiency. Besides BTUs, furnaces receive an annual fuel utilization efficiency (AFUE) rating. This rating reflects a furnace’s actual BTU output. For example, a 100,000 BTU furnace with an AFUE rating of 90 per cent will only deliver 90,000 BTUs of heating power to your home. If you need help sizing your furnace, the experts at Harmony Heating & Air Conditioning would be happy to help.

Furnace installation, maintenance and repair in Calgary

The best way to ensure your furnace is the right size is to get your home evaluated by an HVAC expert from Harmony Heating & Air Conditioning. We provide a full range of heating services, including a home protection plan to help you keep your new system running at its best. We also offer financing options to make it easy to get the unit you need. Contact us today for a free, no-obligation quote.


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