January 11, 2010
By: Greg Tillotson
Gas Log Expert & Webmaster for Hansen Wholesale
We are constantly asked how much it will cost to burn a gas log, or how much gas a particular gas log will consume. In response to these questions, we have recently added the calculator you see below to the left hand navigation of all of our gas log search results pages as well as included the calculated usages and costs on each of our gas log product detail pages.
The amount of gas (Natural or Propane) that a gas log will use is directly related to the BTU rating of the burner system you choose. The BTU rating is in fact the amount of gas that is burned by the gas log set, not the amount of heat that the gas logs generate...particularly when referring to vented gas logs since much of the heat goes up the flue. Ventless gas logs will pretty much produce the same amount of heat in BTUs as the amount of gas that is consumed because they are burned with the damper closed and 99.9% of the heat comes into your room.
However, most consumers do not know just how to translate BTUs into either the amount of fuel used, or the cost attributed to the BTUs, hence the reason we have published this page. In order to translate BTUs into something useful, you must first understand the terminology used by the company you buy your fuel from, whether it be natural gas or propane.
BTU: BTU stands for British Thermal Units, which is a standard measurement of the amount of energy contained in any fuel that is released per hour when it is burned. So a gas log set that has a 40000 BTU burner consumes 40000 BTUs of gas per hour.
Liquid propane is normally sold either by the Pound or by the Gallon. So in order to make use of the BTU rating of a gas log to calculate the amount of propane gas it will consume and attribute a cost to that, we need to know how many BTUs there are in a pound or gallon of LP gas. Here is that information:
1 Pound of LP Gas = 22,000 BTUs
1 Gallon of LP Gas = 91,500 BTUs
Now that you have that information, you can easily calculate the amount of gas any gas log (or gas appliance for that matter) will consume. You simply divide the BTU rating of the burner by the BTUs for the unit of measure you want to check. Here is an example of performing the calculation for a 40,000 BTU gas log:
Pounds of LP Gas Used: 40,000 BTUs divided by 22,000 BTUs = 1.818 Pounds
Gallons of LP Gas Used: 40,000 BTUs divided by 91,500 BTUs = 0.442 Gallons
Calculating the Cost
If you know the cost per pound or gallon of your the LP gas that you purchase, simply multiply this by the calculated usage above. On our website, we actually perform these calculations for you on each one of our gas log product pages...but the calculation we perform is based on the National Average for the cost of Propane Gas, which in fact varies widely by region.
The National Average cost of LP Gas is $2.536 per gallon according to the EIA (U.S. Energy Information Administration) as of January 2010
Using this information, we are able to calculate the average cost in the USA to operate a 40,000 BTU gas log using this formula:
40,000 BTUs divided by 91,500 BTUs/gallon times $2.536/gallon = $1.11 per hour
Natural Gas is normally sold to the residential consumer by the Therm (100,000 BTUs) or Ccf (100 cubic feet = 102,700 BTUs). So in order to make use of the BTU rating of a gas log to calculate the amount of Natural Gas it will consume and attribute a cost to that, we can use these numbers to do the math:
1 Therm of Natural Gas = 100,000 BTUs
1 Ccf of Natural Gas = 102,700 BTUs
Now that you have that information, you can take the BTU rating of a gas log and translate it into useable information by converting the BTUs into Therms or Ccf. To do this, you simply divide the BTU rating of the burner by the BTUs in a Therm or Ccf. Here is an example of performing the calculation for a 40,000 BTU gas log:
Therms of Natural Gas Used: 40,000 BTUs divided by 100,000 BTUs/Therm = 0.40 Therms
Ccf of Natural Gas Used: 40,000 BTUs divided by 102,700 BTUs = 0.389 Ccf
Calculating the Cost
You can find the cost of your natural gas in either Therms or Ccf by looking at your gas bill. If a different unit of measure is used, you will need to convert a little additional math in order to perform the conversion properly. However, according to the EIA, these 2 units of measure are the most commonly used for by gas companies when billing residential consumers. So, take the cost/Therm or Ccf and multiply by the Therms or Ccf used by the gas logs found from the previous calculation above.
On our website, we actually perform these calculations for you on each one of our gas log product pages based on the National Average for the cost of Natural Gas, which varies widely by region.
The National Average cost of Natural Gas is $1.368 per Therm according to the EIA (U.S. Energy Information Administration) for 2008. Based on this information, we are able to calculate the average cost in the USA to operate a 40,000 BTU gas log using this formula:
40,000 BTUs divided by 100,000 BTUs/Therm times $1.368/Therm = $0.55 per hour
Interesting side note: Based on the excersises performed above, we find that the National Average cost of Natural Gas is about half the cost of Propane. So if you have access to both fuels and are contemplating which to choose, then Natural Gas is likely your best choice.