Enter Fireplace and Gas Log Details
Example Data Table
Use these sample rows to test different fireplace sizes and fuel conditions.
| Firebox Width | Depth | Log Width | Fuel | BTU/Inch | Annual Hours | Expected Use |
|---|---|---|---|---|---|---|
| 32 in | 16 in | 18 in | Natural gas | 1,450 | 120 | Light decorative use |
| 36 in | 18 in | 24 in | Natural gas | 1,600 | 180 | Normal living room use |
| 42 in | 22 in | 30 in | Propane | 1,750 | 220 | Large decorative fireplace |
Formula Used
Gross burner input: Log width × BTU per inch × Burner design factor
Altitude adjusted input: Gross input × (1 − Altitude derate)
Useful room heat: Adjusted input × Estimated room efficiency
Vent loss: Adjusted input − Useful room heat
Natural gas use: Adjusted input ÷ 100,000 therms per hour
Propane use: Adjusted input ÷ 91,500 gallons per hour
Annual cost: Fuel units per hour × Annual hours × Fuel price
Flue area: π × (Flue diameter ÷ 2)²
Suggested maximum log width: Firebox width − 2 × Side clearance
How to Use This Calculator
- Measure the firebox front width, opening height, and usable depth.
- Enter the log set width you want to test.
- Select natural gas or propane.
- Enter a burner input rate per inch from the product sheet.
- Add local fuel price and expected yearly operating hours.
- Enter flue, pipe, pressure, and altitude values.
- Press the calculate button.
- Review fit, draft, pipe capacity, heat, and cost results.
- Download CSV or PDF records for project notes.
Vented Gas Log Planning Guide
Why Sizing Matters
Vented gas logs are mainly decorative appliances. They create a flame pattern that looks close to a wood fire. Much of the heat goes up the chimney. A correct size still matters. Oversized logs can crowd the firebox. They can also place flames too close to masonry, screens, or trim. Undersized logs may look weak and uneven. This calculator compares the log width with usable firebox width. It also checks depth, draft area, gas flow, and yearly cost. These checks help during early construction planning.
Fuel and Heat Review
The calculator estimates burner input from log width and input per inch. It then adjusts for altitude. Vented sets often deliver low useful room heat. That is why the tool separates burner input from useful heat. Natural gas cost is estimated in therms. Propane cost is estimated in gallons. The result shows hourly fuel use, annual fuel use, and annual operating cost. This helps compare decorative use with frequent seasonal use.
Draft, Pipe, and Safety
A vented log set needs a working chimney. The flue must stay open during operation. The draft check uses a simple opening-to-flue area comparison. The pipe check uses a simplified capacity table with a safety margin. These values are planning guides. They are not a replacement for local code, manufacturer instructions, or a licensed gas fitter. Always verify gas pressure, connector size, clearances, damper clamp needs, and carbon monoxide alarm placement before use.
Best Use Cases
Use this tool before buying a log set. Use it while comparing several burner sizes. Use it when planning a remodel, masonry fireplace update, or gas line extension. Keep the final product manual nearby. Manual ratings should override generic assumptions. A professional inspection is still needed before installation.
FAQs
1. What is a vented gas log calculator?
It estimates log size, burner input, fuel use, draft needs, pipe capacity, and yearly cost for a vented fireplace setup.
2. Are vented gas logs efficient?
No. They are mainly decorative. Much heat leaves through the chimney, so useful room heat is usually far lower than burner input.
3. How much clearance should gas logs have?
Clearance depends on the product manual. This calculator uses side clearance as an input, so you can match the manufacturer’s requirement.
4. Can I close the damper with vented gas logs?
No. Vented gas logs need an open damper during operation. Many installations require a damper clamp to prevent accidental closure.
5. Does this calculator replace a professional inspection?
No. It supports planning only. A qualified installer should verify venting, gas pressure, pipe size, combustion air, and local code compliance.
6. Why does altitude reduce the burner estimate?
Higher elevations can reduce available oxygen and appliance input. The calculator applies a simple derate after 2,000 feet.
7. Which fuel price should I enter?
Enter natural gas price per therm or propane price per gallon. Use your current utility bill or supplier invoice for better estimates.
8. Why is pipe capacity important?
An undersized gas line can cause weak flames, pressure drop, poor ignition, and unsafe operation. Final sizing should follow approved gas tables.