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What BTU is appropriate for a fire pit? This question has been asked countless times, and the answer isn’t always simple.
There are many factors to consider when choosing a BTU rating for your fire pit. The size of the area you’re heating determines how much space there is to heat with each log that’s burned in the fire, which will determine what size of a fire pit you need.
The type of fuel that can be used (natural gas or propane) and the type of material that makes up your furniture also make a difference in how much warmth you get from burning logs.
Finally, there are even things like wind speed and the ambient temperature outside!
This blog post discusses all these factors so let’s start
What Is A BTU?
A BTU is used as a measuring unit for energy. It stands for British Thermal Unit and it’s the amount of heat needed to raise one pound of water by one degree Fahrenheit.
Simply put, it’s the amount of energy needed to raise the temperature of one pound (.454 kilograms) of water by one degree Fahrenheit (.555 degrees Celsius).
In fact, there are several different types of BTUs. One British Thermal Unit (BTU), which equals about .293 watt-hours or joules per hour and approximately equal to ten 100-watt incandescent light bulbs running for an hour.
Another common unit of measurement is millions of BTUs per day – enough power in a single day to heat up three gallons ()of water from freezing point (-17.778 degrees Celcius)to boiling point (100 degrees Celsius).
What BTU Is Appropriate For A Propane Fire Pit?
A BTU of between 40,000 and 150,000 BTUs is ideal for a fire pit. 40,000 BTUs is best for most small patios or decks. If you have a med-large patio or deck then you should choose between 60,0000 and 100,000 BTUs. A 150,00-BTU fire pit will work the best on a large patio or deck.
The amount of BTUs a fire pit has is measured in terms of how much heat it can generate.
It basically tells you the power output and not the size or what heating element should be used for your outdoor fireplace equipment.
In general, there are three types of BTU levels: low, medium, and high.
There are quite differences between each type so let’s take a look at them individually to find out which one works best with your needs.
Low-BTU Pit Equipment
This category includes most portable propane models but does not include any freestanding options because they have too many moving parts to make sense for this category.
These units usually have about 14,000 BTUs and are good if you want to cook over the pit but still need a little bit of warmth for your outdoor living space such as an open patio or deck.
Medium-BTU Pit Equipment
This is where it gets fun with fire pits because there are so many great options available in this category that can be used on decks and patios up to 200 square feet.
If you use propane burners in your equipment then these models will generate around 18,000 BTUs while natural gas models may range from 22,000 – 36,300 BTUs depending on what type of heating element they use.
High-BTU Pit Equipments
This category includes dedicated free-standing fire pits with large stainless steel burners and huge glass panels.
They generally range from 30,000 – 60,000 BTUs depending on the brand you buy and can generate enough heat to warm up a space of over 350 square feet.
How Much BTU Do I Need For My Propane Fire Pit?
The BTUs should be high enough for providing warmth during the nighttime. On average, a 30-inch fire pit will require 50k – 70k BTU while larger models can go up to 100 k or more.
You need to check how much heat it throws off before buying one of them because if you buy something that has very low heating power then it won’t do justice in your patio area which means you might not like this product after using it once or twice.
How Much BTU Do I Need To Cover My Area?
(These numbers are an estimation, many factors could reduce numbers)
|10,000 BTUs||150 sq ft|
|20,000 BTUs||250 sq ft|
|40,000 BTUs||550 sq ft|
|60,000 BTUs||800 sq ft|
|80,000 BTUs||1,200 sq ft|
|160,000 BTUs||2,500 sq ft|
What Type Of Fire Pit Generates The Highest BTU?
There are several types of fire pits available in today’s market which include wood, propane, and natural gas.
Wood Fire Pit
30,000 to 100,000 BTUs Wood burning fire pits are an extremely common choice for consumers.
They provide a traditional look and feel to the patio, plus they create a warm cozy environment that people of all ages can enjoy.
There is something so calming about staring at bright flames licking against the night sky while listening to the crackling wood. If I had to choose one type of fire pit to have in my backyard, it would hand down be this type.
Propane Fire Pit
40,000 and 150,000 BTUs: A propane fire pit is a type of outdoor fire pit that uses propane gas as fuel instead of wood or charcoal. It’s more similar to a portable grill than it is to an ordinary campfire, so some purists might not even classify it as such.
Natural Gas Fire Pit
30,000 to 60,000 BTUs: A natural gas fire pit is a type of outdoor fireplace, which is used for both heating and cooking. Being highly portable, these can be installed pretty much anywhere from backyards to patios and balconies.
They are fueled by natural gas or propane, depending on your preference.
The BTU ratings on fire pits are usually only an approximation. This is because there are so many different variables in their usage that can cause them to require more or less energy at any given time.
Such as how much smoldering material you have in your pit, the rate at which it’s burning, and what type of fire pit you are you’re using.
Some people ask me this question and I always say, “It depends.”
There is no answer that fits all fire pits because what type of fire pit generates the highest BTU rating really depends on a couple of factors: specifically, how big it is and what kind of fuel you’re using.
Some very large propane burning fire pits may actually put out more heat than some wood-burning pits. This is because they burn at such a high temperature (around 3600 degrees Fahrenheit).
So even though there might be fewer total BTU’s released from the wood-burning unit; those same BTUs are much hotter when they come out.
This makes for quite an impressive display as you can see in the picture to the right.
For reference (and for this discussion) we’ll go with a typical wood-burning fire pit that has a thermal output of 100,000 BTU’s.
You must remember that this number is based on the outside air temperature and wind conditions because even though it may be 90 degrees Fahrenheit outside; if there’s a 20 mile per hour breeze you could lose up to half of your total BTUs due to frictional heat loss.
On average one cord of green, seasoned hardwood will burn approximately 3 hours at max blaze when burned in an open-air environment.
This type of fire pit is typically suitable for mild climates where winter lows stay above 30-40 degrees Fahrenheit and summer highs rarely exceed 100 degrees Fahrenheit.
However, if you’re in a hotter climate where the mercury climbs well into the triple digits during summer months then you should consider a large propane burning fire pit instead because it won’t lose nearly as many BTUs to frictional heat loss due to wind.
In other words, your 50,000 BTU propane fire pit will only lose half of that (25,000) due to wind; whereas your 100,000 BTU wood-burning pit will most likely lose upwards of 80% (80,000).
The 4 basic factors that determine how much heat is released by any given fuel are oxygen supply; mass; surface area; and exposure time.
The greater the exposure time is for any given element; the greater amount of heat is released. The surface area for any given element is also important because the larger than the surface is; the more BTUs are released.
However, if one factor (like oxygen supply) remains constant then you can divide by that number to determine how much energy will be expended in a given time frame.
Therefore, if you take your 100,000 BTU wood-burning fire pit and divide it by 3 hours – you wind up with ~33,333 BTU’s per hour.
Conversely, if your 50,000 BTU propane fire pit was only exposed to air for 1 hour it would expend approximately 16,668 BTU’s per hour.
Again, this is strictly hypothetical because we do not know exactly what the wind conditions will be in any given environment. In a typical scenario, this propane fire pit would probably expend around 20% less BTUs due to frictional heat loss from wind.
So which type of fire pit is hotter? Well, that one really depends on your specific situation and intended usage.
If you’re in a windy area then using a large propane burning unit may not be a good idea because you could lose anywhere from 30-70% of its total BTU output.
However, if you’ve got a smaller wood-burning pit – especially when operated at night when it’s cool enough for all four elements (oxygen supply, mass, surface area, and exposure) to remain constant – then there’s a chance that wood-burning fire pit could actually be hotter than its propane brother.
The BTU number is a measure of how much energy your fire pit needs to produce in order to maintain an average temperature.
If you have low temperatures, then the higher the BTU rating will be necessary for maintaining a warm environment.
Conversely, if you live in a warmer part of the country, it might not require as high a BTU rating but may need additional measures such as insulation or increased air circulation at night so that colder winds don’t cause problems with cooling down.