What is the Meaning of BTU?

How to determine what BTU you need. "The Meaning of BTU" Focus on Purchasing:

• Air Conditioning Systems
• Air Conditioner Condensers
• Heat Pump Condensers
• Air Handlers
• Accessories

What Is BTU?

You’ve probably come across the acronym BTU a couple of times when shopping for air conditioners. It’s a term that is used in air conditioner descriptions as well as product names. BTU is found not just on air conditioners but on water heaters and furnaces as well.

BTU stands for British Thermal Units. The textbook definition of BTU is the amount of energy that is required to raise the temperature of 1 pound of water by 1°F at sea level.

When BTU is used in air conditioning systems it’s usually referring to how many units of energy an air conditioning system requires in an hour to either remove or add air.

Ironically, a high BTU isn’t always the best solution. When you use an air conditioner with a high BTU than what is needed, it may cause your air conditioning system to cool too quickly. The air conditioning system will then cycle off and if you want to maintain a preferred temperature, you’ll have to cycle on your unit again.

What’s wrong with cycling your air conditioner system on and off within such a short period of time is that your air conditioner’s compressor gets overworked. In fact, if it happens frequently, you can be sure that your unit’s compressor will have a short lifespan.

When you use an air conditioner that has less than the required BTUs you won’t be able to get the level of comfort you desire. The excessive heat load will prove too much for your air conditioning system to handle. Your AC unit will run continuously and never achieve the preferred temperature level. This will lead your unit to have a shortened lifespan.

How To Determine The Number Of BTUs You Need

Because of the reasons stated above, it is always important to take the square footage recommendations into consideration. AC units normally have square footage recommendations indicated on the packaging.

To effectively use the recommendations, you’ll need to measure the square footage of the space you plan on installing the AC unit.

Below is a chart that has recommendations on the amount of BTUs you need for various sized spaces.

Square Footage	BTUs Required	Square Footage	BTUs Required
150 sq. ft.	5,000 BTU’s	700 sq. ft.	14,000 BTU’s
250 sq. ft.	6,000 BTU’s	1,000 sq. ft.	18,000 BTU’s
300 sq. ft.	7,000 BTU’s	1,200 sq. ft.	21,000 BTU’s
350 sq. ft.	8,000 BTU’s	1,400 sq. ft.	23,000 BTU’s
400 sq. ft.	9,000 BTU’s	1,600 sq. ft.	25,000 BTU’s
450 sq. ft.	10,000 BTU’s	1,900 sq. ft.	28,000 BTU’s
550 sq. ft.	12,000 BTU’s	2,700 sq. ft.	36,000 BTU’s

 

For the most part square footage recommendations are usually correct, however there are some variables you need to pay attention to when determining how many BTUs your ideal air conditioner needs to have.

Say for instance, you want to use the air conditioner in a two-story building. In this scenario, the second story has a higher temperature as it receives direct sunlight. It is recommended that you have up to 10% more of the recommended BTU as this will help you get a better approximation of how much cooling power you need.

However, if the space you’ll be using the air conditioning in has lots of shade, but not a lot of sunlight exposure you’ll want to find an air conditioner that has 10% less the recommended BTU. Even though this isn’t always recommended it’s better to have an AC unit that has more than BTUs needed than have one that has insufficient BTUs.

If you’re using the AC for a space that will be hosting more than one person, you should add an additional 600 BTUs to the recommended number of BTUs.

Perhaps you plan to have the air conditioning system installed in the kitchen where there are appliances that generate heat, you will require to add 4,000 BTUs to what’s recommended for that square footage.

Finally, you want to consider whether the space you’ll be installing the AC unit is closed off or open. The square footage recommendations made above are for closed areas. This is important to note because if the space you intend the AC for opens up to another area within the house without the option of a door, then you need to think of the two spaces as one.

Recommended BTUs for Your Furnace

BTUs aren’t only used in air conditioners but in furnaces as well as water heaters. The recommended BTUs for furnaces are different from those of air conditioners so you can’t use the table above for load calculations.

Even though calculating how many BTUs your furnace needs requires complex calculations, there are basic rules that can guide you get the best BTU estimate for your home.

If you live in climate that’s cool, you need to go for a furnace that produces anywhere between 40 and 45 BTUs for every square foot. This means that you’ll require a furnace that produces a maximum of around 112,500 BTUs to produce sufficient heat for a 2,500 square foot home.

A more efficient way of calculating a furnace’s BTU estimate is by using the degree-day calculation. You’ll need to use the month of July as a factor. This though only applies for gas-powered furnaces. Natural gas used in a furnace is charged by the therm. Therms are usually listed on your home’s gas bill. To determine the number of BTUs a furnace is likely to produce within an hour use the following formula:

50 x furnace efficiency x heating therms = load in BTUs/hour

For instance, let’s say that you use 1,500 therms annually. If the number of therms used in the month of July is 25 and the furnace has an efficiency of 82%, this is how you would calculate your recommended furnace size:

Subtract your July therm usage for the annual figure, that is,

1500 - (25x12)

Then do:

50 x 0.82 x (1500 – (25x12)) = 50,000 BTU

According to this calculation your home needs a furnace with a rating of 50,000 BTU to keep your home sufficiently heated.