What are BTUs?

Knowing what a BTU (British thermal unit) lays the foundation for understanding the capacity of gas and oil furnaces. A furnace with 70,000 BTUs will use 70,000 BTUs of gas or oil per hour.

BTUs measure how much energy it takes to raise the temperature of two cups (equivalent to one pound) of water one degree Fahrenheit. All furnace and boiler manufacturers use BTUs to describe the sizes of their systems.

BTUs and Efficiency Ratings

How many of those BTUs go toward heating your home is not solely an issue of the system size in BTUs, but rather, how efficiently it uses that fuel to warm your home. All gas and oil furnaces have energy efficiency ratings called AFUE (annual fuel utilization efficiency) that indicate how much of the fuel actually goes toward heating instead up the chimney as waste gases and water vapor.

When you’re choosing a new system, you and the HVAC contractor will have to find the best size for your home. Besides assessing the overall energy efficiency of your home, the exercise will involve exploring the relationship between the AFUE of the systems you’re considering and their BTU capacities.

Long-Term Considerations

A system with an AFUE rating of 80 won’t provide as much heat as one with an AFUE of 95 even though each may use the same amount of fuel. A system with 80,000 BTUs and an AFUE of 95 will provide 76,000 BTUs of heat, while one with an 80 AFUE will put out just 64,000 BTUs. It makes sense to opt for the more efficient system because the long-term fuel savings a smaller but more efficient system provides will insulate you from rising fuel costs

In this climate where winter heating is a given, it makes sense to weigh the benefits of high efficiency versus systems that have higher BTU capacity. To learn more, contact Sobieski Services, Inc. Our goal is to help our customers in Pennsylvania, Delaware, New Jersey and Maryland learn more about home energy efficiency, plumbing and HVAC systems to live in healthier and more comfortable homes.