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What Size Furnace Do I Need & How is it Determined?
If you are shopping for a new furnace or are experiencing problems with your current one, it is important to consider the size. Size is an often overlooked factor when selecting the best furnace for your home; however, it can make all the difference in the world.
Why Does Furnace Size Matter?
The size of your furnace works in comparison to the size of your home. Consider the following:
1. Comfort
Is the furnace big enough to comfortably heat your entire home? Having a furnace does no good if it is not maintaining a comfortable temperature in the house.
2. Energy Efficiency
Is the amount of energy being spent reasonable? A small furnace works extra hard, while a big furnace overcompensates. Both waste energy.
3. Lifespan
If a furnace is the wrong size for a home, you can count on the lifespan being shorter.
If the Furnace is Too Big
A too-big furnace will likely overperform. Instead of maintaining a steady neutral, it will constantly switch from on, to off, to on again. This is expensive and inefficient. It can also damage the entire unit, which creates long-term costs and problems.
If the Furnace is Too Small
Naturally, a small furnace is going to have a difficult time warming or cooling a large house. This is why it is important to weigh factors such as floor levels, size, doors, windows, etc. to ensure that your furnace is big enough to perform its job…without being so big that it costs you.
How is Size Determined?
Size is based on capacity. Capacity is based on how much heat the furnace is capable of producing.
Determining the Heating Capacity
A furnace’s capacity is measured in British Thermal Units (BTUs). This is the amount of fuel energy utilized in operation. A BTU of 90% means that the furnace produces 90,000 BTUs of heat, etc.
Basically, an 80% AFUE furnace wastes 20% of its energy. A 95% AFUE looss 5% of its energy out of the vent or flue.
Manual J Load Calculation
The Manual J calculation plays a key role in determining the right size of furnace for your home. This calculation gives size in exact BTUs per hour and considers factors such as location, sun, ductwork, possible leakage, windows, doors, and house size.
