A Guide to Understanding British Thermal Units

If you’re in the process of shopping for a new HVAC system, you’re going to encounter the term “BTU.” You may be wondering: what is BTU? Read on to learn what it means and why it matters. Understanding BTUs is the best way to find the right heating or cooling system for your needs.

What is BTU?

So, what is BTU, exactly? To begin, the acronym, “BTU”, stands for “British Thermal Units.” This unit of measurement refers to the amount of energy it takes to raise the temperature of one pound of water by one degree Fahrenheit. (Technically, we should add “at sea level,” but that’s not relevant to the HVAC discussion).

This unit of measurement has been in use since the late 1800s. It’s since become a commonly used industry term for rating and sizing heating and cooling appliances. Those appliances include both the whole home and portable air conditioners. They also include stoves, heat pumps, and heaters powered by oil, natural gas, electric, solar, and beyond.

BTUs in Heating and Cooling

As you browse through different options for an air conditioner, furnace, or HVAC system, you’ll see the term “BTU.” It shows up in many different ways. BTU output, BTU input, BTU number, BTU/H, etc.

Here are some answers to basic questions you might have about how BTUs are used in the world of HVAC systems.

What is BTUs Measurement Process for Both Heating and Cooling?

There is a slight difference in how the term is usually applied between air conditioning systems and heating systems.

A BTU rating for heating equipment usually refers to the amount of heat the appliance can generate. With air conditioners, the BTU rating refers to their capacity to remove heat from the air.

In each instance, it’s about how much energy the unit needs to generate for the air to be at a different temperature. This is what’s called “BTU input” – not to be confused with BTU output.

What is BTU Output/Input?

The typical BTU rating of a heater refers to the amount of heat it can generate. With AC, the BTU number is about the energy required to transfer heat out of the home.

So, what is BTU input? Here, the input is about capacity. Producing and removing heat both require energy, and different units have different capacities to heat/cool different spaces.

However, there’s also “BTU output,” also known as “heat output” (when applied to heaters). This doesn’t refer to the energy required to run heating or cooling equipment. Instead, it refers to the amount of usable heat that is produced (or removed).

If you’re wondering why there’s any difference between the two, that’s because of the efficiency factor. Different units operate on different levels of efficiency and are rated accordingly. The most common type of rating is the Seasonal Energy Efficiency Ratio (SEER) rating.

The efficiency rating factors in with the input rating to calculate the BTU output.

Also, just for clarity’s sake, “BTU rating” and “BTU number” are interchangeable terms commonly used by manufacturers. These could refer to either the BTU input or BTU output.

What are BTUs per Hour?

Here’s where things may get even more confusing. A BTU rating (or number, or input/output) doesn’t mean the number of BTUs alone. It refers to the BTU/H or BTUs per hour. There’s a good reason for this.

Without measuring per hour, the BTU isn’t an effective unit of measurement for cooling or heating capacity. How long does a furnace or air conditioner take to use a certain amount of energy? Without that information, a BTU number doesn’t have much use.

By rating this energy consumption on an hourly basis, the measurement becomes standardized and applicable for all heating and cooling equipment.

How Many BTUs Does Your Home Need?

This question is more important than it may seem on the surface. It’s not about making sure you’re over a certain minimum capacity and then you’re all set.

Your home has specific heating and cooling needs. Those needs relate to the size, shape, location, and specific details of your home.

The square footage of the space in question is the key factor in selecting the appropriate BTU rating. Once you know the size of the space you need to heat or cool, you can easily find charts online to calculate your BTU needs.

However, these charts can’t offer the same degree of expertise as a trained HVAC tech. These charts tend to assume standard 8 ft. ceiling heights. They also make broadly generalized estimates about your local climate based on a much bigger geographical region.

There are other important factors that online charts don’t take into account. For instance, the layout and floor plan of your home make a huge difference.

It’s always best to seek professional consultation from a local HVAC contractor. This is the only way to ensure the ideal sizing of your heating and cooling equipment.

The Importance of Proper Sizing

In case there’s any confusion on this, “sizing” isn’t about the physical size of the unit. It’s about having a heating and/or cooling system that’s designed to accommodate the space in question.

If the unit is undersized, this presents some obvious problems. Without having the necessary heating or cooling capacity, your system won’t effectively heat or cool your home. It will strain to service your space.

This makes for poor efficiency and accelerates the general wear and tear on the machinery, shaving years off its lifespan. It will run nonstop and cost a fortune in utility bills.

If it’s not powerful enough to heat or cool your home, it’s not powerful enough to heat your home. But what if it’s powerful enough to heat or cool a much larger space?

Oversizing has problems of its own. The heating and cooling will be very sudden, uneven, and lead to “short cycling.” Heating and cooling take place gradually rather than through powerful blasts. It’s better for your equipment and more comfortable for the household, especially in terms of humidity.

Short cycling means your system will be constantly switching on and off due to how quickly temperature settings are reached. This can damage your equipment and limit its lifespan.

Factors to consider in HVAC sizing range from where your home is located in the United States to how many windows you have. Quality of insulation, ceiling height, and where the unit should ideally be installed are all important considerations.

Get the BTUs You Need

Are you still wondering… what is BTU? That’s okay! If you’re in South Jersey, reach out to Laury Heating Cooling & Plumbing with any questions for help determining your HVAC needs.

Your home is unique, and it has specific qualities that an online chart won’t take into account. With an experienced and customer-centric HVAC tech, you can make sure your home gets the heating and cooling your family deserves.

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