How many BTUs you need to heat your home, shop, garage, and more!

What size heater do I need to heat my home, garage, or workspace? It seems like a relatively simple, straightforward question. Yet the answer is anything but simple - requiring a deep dive into the science of energy, spatial geometry, climatology, and construction technology. 

The answer to the common question “How many BTUs do I need to heat my house?” begins with an understanding of energy production and the British Thermal Unit. One BTU is the amount of energy required to raise the temperature of one pound of water by 1 degree Fahrenheit. The measure itself is very small, but it is the base calculation upon which energy use is built. In 2018, the United States used approximately 101.3 quadrillion BTU of energy

Calculating the number of BTUs needed to heat an area

In terms of heating and cooling system, the underlying calculation is how much you want to add, or remove from the air inside a building. That might depend on a number of other variables, such as square footage and climate - but the starting point is how many degrees you want to move the inside temperature, and how many BTUs are required to do so. There are calculators available to help homeowners factor the right sized unit, but there are also some rules of thumb that can be followed. For example, a 300 square foot room typically requires 7,000 BTUs to maintain a comfortable temperature, while a 1,000 square foot room requires 18,000 BTUs.

A simple formula to determine your heating needs is: 

(desired temperature change) x (cubic feet of space) x .133 = BTUs needed per hour. 

What factors can impact your heating needs?

1. Climate and weather

Climate also plays a role in determining your energy needs. Warmer climates along the southern part of the United States - considered Zone 1 or 2 - require 30-40 BTU per square foot. The middle part of the country - Zone 3 and 4 - require between 40-45 BTU per square foot, while the northern areas of Zone 5 need up to 60 BTUs per square foot. In the simplest terms, the colder, or warmer, the outside air, the more energy you’ll need to move the internal temperature of a building. Once you know your climate zone, and the corresponding BTU requirements for your area, you’ll be able to find a general number for your home. For example, in zone 3 to 4, which typically requires 40-45 BTU per square feet, you can determine that a 2,500 square foot home would need a 100,000 to 112,000 BTU furnace. 

2. Average square and cubic footage

Another variable in determining your energy needs is space - both in terms of square footage and cubic footage. Naturally, the bigger the space the bigger the need - yet it’s important not to fall into the bigger is better attitude. Purchasing an oversized heater or air conditioner creates a different set of concerns - such as strain on compressors that frequently cycle on and off, excessive noise, and overall reduced efficiency. 

Using our formula from above, a 1,000 square-foot workspace with 8-foot ceiling height means you’ll be heating 8,000 cubic feet of space. If the temperature outside is 30°F and you’d like it to be 70°F in your garage, the desired temperature change is 40°F. Those two numbers multiplied by .133 reveals you’ll need a little more than 42,500 BTUs per hour to keep your workspace at 70 degrees. 

Because propane is a clean and efficient fuel that contains more than twice the energy of natural gas, it’s a natural choice for heating systems in any climate. For instance, a 100,000 BTU natural gas furnace burns around 97 cubic feet of gas in an hour, while the same sized propane furnace burns on 40 cubic feet in an hour. The higher the efficiency rating on your heater or air conditioner indicates that more of the energy used is directed toward your heating or cooling needs. 

3. Building material and quality

Also affecting this calculation is the quality and type of building material, and the age of the home. Additional windows that let in more sunlight, or cold air, change the calculation, as does the use of insulation throughout the home. Older homes that are drafty, or not well insulated, will require additional heating capacity. Air conditioners in homes that have multiple south-facing windows likewise will require increased capacity to cool the air heated by sunlight. 

Installers should measure the entire house, taking into account the layout of the rooms, the location of the windows, potential shade, insulation and climate data to arrive at the correct heating and cooling load calculations to determine the appropriate sized heating or cooling system. 

Contact Ferrellgas for your heating needs

While there’s not a simple answer to the right size heating or cooling system for your home, shop, or garage - by considering a few simple elements and calculations it’s easy to determine the right unit for your structure. Knowing a little bit of information about your building, your climate, and your heating and cooling needs can help you find the solution that will keep you and your family comfortable through every season. 

To find out what propane solutions are best to help heat your space, get in touch with your local Ferrellgas office, where our experts can give you a great propane price and determine what the best options for your home, business, or farm will be.

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