To understand how BTU relates to your HVAC system, we have to first define a few things.
What BTU means
BTU stands for British Thermal Units and it’s a traditional way of measuring heat energy. A typical furnace may have 80,000 or 100,000 BTU.
In order to understand BTU, it's important to know what AFUE means. AFUE stands for annual fuel utilization efficiency. In simpler terms, it’s how effectively it turns gas into heat. For example, a furnace with 80% efficiency, converts 80% of that energy into heat, and loses 20% in the heating process.
How it relates to your HVAC system
When looking to buy a furnace or AC, size is crucial and understanding BTUs will help you better decide which size furnace and efficiency is right for you. The size of the furnace will not only affect the comfort of the home but also the price of your energy bill.
Buying a furnace that’s too small for your home will tempt you to crank the thermostat higher than needed and constantly run the furnace. Over time, this will lead to wasted energy and higher bills.
If you purchase an AC unit that’s too small for your home, you will notice that it will constantly run throughout the day and still not manage to get to that desired, cool, temperature. As you can guess, your electric bill will reflect that outcome.
Buying a furnace that’s too big for your home will overheat spaces that aren’t necessary. Over time leading to tons of wasted energy, higher bills, and more wear and tear of the furnace due to the furnace turning on and off more frequently.
If you purchase an AC unit that's too big for your home, the thermostat will continuously turn on and off due to the ac running on short bursts. Since, the AC is so big, it will reach that desired temperature quickly, but it will alert the machine to turn off quickly as well. This can lead to more wear and tear on both your furnace and your AC as well as not removing the humidity that can cause your home to not feel comfortable.