How to Measure For Gas Fireplace Logs

Gas Logs from Home of Decor

With a few simple measurements and calculations you can quickly determine your options for gas logs.  Once you know the size and BTU’s that best fit your fireplace and room size, you can choose the gas fireplace log arrangement that best fits your decorating style.

Measure the Firebox

It’s important to choose the right sized log set for your firebox; choosing one which is too large will greatly reduce the efficiency of the system, while one which is too small won’t be as beautiful as one which fills the space completely. 

The first step is measuring your firebox, or the actual place where the fire will occur.  There are four basic measurements to collect:

  1. The front opening from edge to edge
  2. The rear width of the firebox from corner to corner.  Frequently this number may be smaller because some fireboxes angle inward.
  3. The depth of the firebox from the front opening to the rear wall.
  4. The height of the firebox opening.

Make A Few Necessary Adjustments

These measurements give you the dimensions of your firebox, but must be adjusted for other factors before choosing your log set. 

  • A minimum space of 2” must be maintained between the log set and the side walls of the fireplace.
  • If you are using a vent free or propane gas system, you’ll need an additional 4” of clearance for the required safety pilot kit.  The kit is optional for natural gas systems.  Safety pilot kits are much more convenient than standard on/off valves which require you to manually light the logs each time you want a fire. 
  • Including a remote control for your gas logs means that you will need to reduce the maximum front size of the gas logs by an additional 6-8” to allow for the system.  Remote systems can range from a simple wall switch to a wireless system that allows you to increase or decrease the flame size from across the room.

Calculate the Number of BTU’s

Once you’ve calculated the final maximum size of your gas log set, the next step is determining the maximum number of BTU’s (British Thermal Units) for your room size.  Begin by calculating the total cubic feet of the room (multiple the room length x width x height).  Divide this number by 50, then multiply by 1000 for the recommended BTU amount for the room.  If there is an adjacent room that is not separated by a door, include that area in the total as well.

Now armed with these important numbers, you can calculate the size of your gas log set using the chart below.  Each manufacturer’s sizing is slightly different, so confirm with the company before making your final purchase. 

Log Set Size

Front Width

  Rear Width 

   Depth  

BTU Range

12"

12"

12"

9"

25,000

16"

16"

12"

9"

30,000 - 50,000

18"

18"

15"

12"

40,000 - 75,000

19"

19"

15"

12"

40,000 - 75,000

20"

20"

15"

12"

40,000 - 75,000

24"

24"

20"

12"

50,000 - 90,000

30"

30"

24"

12"

65,000 - 90,000

36"

36"

30"

13"

90,000 - 120,000

42"

42"

36"

20"

105,000 - 150,000

48"

48"

42"

20"

105,000 - 150,000

54"

54"

48"

20"

105,000 - 150,000

60"

60"

54"

20"

105,000 - 150,000



The next step is choosing a gas log set.

Selected Merchants
Home of Décor offers a complete range of RH Peterson Real Fyre gas logs for vented and ventless fireplaces.  Once you have your fireplace size and fuel type, you can quickly see a comprehensive selection of gas fireplace logs which will fit your firebox.  Their prices are great, and they frequently offer free shpping.

HomeClick.com It’s easy to find the right logs on this site, since you can refine your source by gas log type (vented or vent free gas logs), firebox width, fuel type, or price range.  Prices on HomeClick.com are among the lowest you’ll find, and they frequently offer great sales, free shipping, and even financing options.