Gas Log Sizing Calculator

Size gas logs with clear measurements accurately. Compare heat output, fuel demand, and fit limits. Build a safer fireplace plan before ordering today online.

Enter Fireplace and Fuel Details

Inches across the fireplace front.
Inches across the fireplace back.
Measure from front to back.
Opening height in inches.
Space left on each side.
Space behind the burner.
Space before the burner.
Feet.
Feet.
Feet.
Percent estimate.
Feet above sea level.
Feet from supply point.
Nominal inside size in inches.

Formula Used

Usable width = smaller fireplace width − two side clearances.

Usable depth = firebox depth − back clearance − front clearance.

Suggested log width = usable width × selected fill factor.

Room volume = room length × room width × room height.

Room heat estimate = room volume × selected BTU factor.

Log input estimate = suggested log width × BTU per inch × flame factor.

Altitude derate = 1 − altitude adjustment.

Recommended input = larger heat estimate × altitude derate.

Natural gas use = BTU per hour ÷ 1030.

Propane gallons = BTU per hour ÷ 91500.

How to Use This Calculator

Measure the front width, back width, depth, and height of the fireplace opening. Enter clearances recommended by the log set or burner maker. Choose the fuel type, vent type, heat goal, and preferred fill style. Add room dimensions for a heat estimate. Press the calculate button. Review the suggested log width, nearest common log size, BTU estimate, fuel use, and warning notes. Use the result as a planning guide before purchase.

Example Data Table

Front Width Back Width Depth Fill Style Suggested Size Estimated Input
36 in 30 in 20 in Balanced 18 in About 35,000 BTU/hr
42 in 36 in 22 in Full 24 in About 46,000 BTU/hr
30 in 26 in 17 in Compact 12 in About 24,000 BTU/hr

Gas Log Sizing Guide

Gas log sizing starts with the firebox, not the log set. A good set must sit inside the opening with safe space around the burner, grate, flames, and controls. The smallest width, usually the back width, controls the fit. Depth matters too, because many burners need room at the front and rear.

Measure Before Choosing

Use a tape measure on the inside opening. Measure the front width, back width, height, and depth. Keep the tape level. Write each value in inches. Do not guess from the old grate. Old parts may be bent, oversized, or unsafe for a new burner.

Clearance and Fit

The calculator subtracts side, rear, and front clearances. This creates a usable area. The selected fill style then controls how much of that area should be covered by logs. A compact style leaves more visible space. A full style gives a wider look, but it needs better clearance.

Heat Planning

The tool also estimates room heat demand. It uses room volume and a selected heat goal. Decorative use needs less output. Strong heating needs more output. The calculator compares room demand with an estimated burner input. This helps you avoid a set that looks right but heats poorly.

Fuel Use

Fuel use is estimated from the input rating. Natural gas is shown in cubic feet per hour. Propane is shown in gallons and pounds per hour. These values help compare running cost, tank needs, and supply capacity.

Safety Review

This calculator is not a final installation approval. Gas appliances need correct venting, pressure, pipe sizing, combustion air, and approved fittings. Vent-free products may have extra room volume limits. Vented products need a suitable chimney or flue. Always follow the appliance manual and local rules. Hire a qualified gas technician when connecting fuel lines, testing leaks, or changing appliance parts.

FAQs

1. What size gas logs do I need?

Measure the fireplace front width, back width, depth, and height. The correct size is usually smaller than the opening because clearances must be maintained around the burner and logs.

2. Should I use front width or back width?

Use the smaller width for sizing. Many fireplaces taper toward the back, so the back width often controls the largest safe log set.

3. What does fill style mean?

Fill style controls how much of the usable width is occupied. Compact leaves more open space. Balanced suits most layouts. Full gives a larger appearance but needs more clearance.

4. Are vented and vent-free logs sized differently?

Yes. Vent-free sets often have stricter room, clearance, and oxygen rules. Vented sets depend more on chimney condition and draft. Always check the product manual.

5. Can this calculator size gas pipe?

No. It gives a simple line load score for planning. Final pipe sizing needs fuel pressure, pipe material, fittings, appliance demand, and local code tables.

6. Why is room volume included?

Room volume helps estimate heat demand and combustion air needs. A small room may overheat quickly or require extra review before using certain appliances.

7. Does altitude affect gas log sizing?

Altitude can reduce appliance performance. The calculator applies a simple derate estimate. Product manuals and local rules should guide final input ratings.

8. Is the result safe for installation?

No calculator can approve installation alone. Use this result for planning. Confirm all dimensions, ratings, clearances, venting, and gas connections with a qualified professional.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.