Inputs
Enter outdoor appliances, then size using length and pressure assumptions.
Example data table
This example shows common outdoor loads and a single run length.
| Scenario | Gas | Longest length | Loads (BTU/h) | Design margin | What you get |
|---|---|---|---|---|---|
| Backyard grill + patio heater | Natural gas | 60 ft + 10% fittings | 60,000 + 40,000 | 10% | Required ID and nearest schedule 40 size |
| Small greenhouse heater | Propane | 80 ft equivalent | 80,000 | 10% | Recommended copper tubing OD from table |
Real projects need local code tables, regulator specs, and inspection.
Formula used
- Total effective load = Σ (Appliance input × Use%).
- Design load = Total effective load × (1 + margin%).
- Natural gas flow (CFH) = Design load ÷ Heating value (BTU/ft³).
- Equivalent length = Straight × (1 + fitting allowance) + extra length.
- Natural gas sizing uses low- or high-pressure pipe sizing equations to compute required inside diameter, then selects the nearest standard size.
- Propane sizing uses a low-pressure copper tubing capacity table (kBtu/h) at a chosen length.
How to use this calculator
- Choose the fuel type and the sizing method that matches your supply pressure.
- Enter the longest run length to the farthest outdoor appliance.
- Add a fitting allowance or extra equivalent length for bends and valves.
- List each appliance input rating and optional “Use %” value.
- Click Calculate to see the recommended size above the form.
- Use the export buttons to save your result as CSV or PDF.
Demand planning for outdoor zones
List every appliance that can burn gas, then assign a Use % to reflect how often devices run together. The calculator multiplies each input rating by the Use % and totals the diversified load, helping avoid oversizing when a grill and heater seldom operate simultaneously. Add a design margin, such as 10%, to cover startup surges and future additions.
Converting load to gas flow
For natural gas, the tool converts the design load to cubic feet per hour (CFH) using CFH = BTU/h ÷ heating value. With a 100,000 BTU/h design load and a 1,000 BTU/ft³ heating value, the estimated flow is 100 CFH, which becomes the basis for pipe sizing. If entered in kW, it converts using 1 kW = 3,412.142 BTU/h.
Accounting for length and fittings
Pressure loss is driven by run length and restrictions. The calculator builds an equivalent length using straight length × (1 + fitting allowance) + extra length. A 60 ft run with a 10% allowance is treated as 66 ft, and you can add fixed equivalent footage for valves, quick-connects, or bends. Longer equivalent lengths push the recommended size upward.
Choosing a pressure method
Low-pressure systems operate around 7–11 inches water column, so the low-pressure equation uses an allowed drop (ΔH) and equivalent length to estimate the required inside diameter. If you have a higher-pressure supply, the high-pressure option uses upstream and downstream pressures (psig converted to absolute) to model capacity at a larger pressure differential. Selecting the correct method aligns results with your regulator stage.
Using the recommended size
After the required inside diameter is calculated, the tool selects the nearest larger standard schedule 40 size for natural gas, or a copper Type K tubing OD for propane tables. For propane, the table length rounds up to the next listed distance so capacity is not overstated. If your route is exposed or includes many fittings, upsizing one nominal step can add resilience while keeping pressure drop conservative.
FAQs
How do I choose the sizing method?
Use low-pressure when appliances are supplied at inches water column from a final regulator. Use high-pressure when you have a higher psig distribution line before the final regulator and you know upstream and allowed downstream pressure.
Why does equivalent length change the size?
Fittings, valves, and bends add friction similar to extra pipe. Equivalent length increases the modeled run, which raises the required inside diameter for the same flow, reducing the chance of low pressure at the appliance.
What heating value should I enter for natural gas?
Use the value from your utility if available. If you do not have it, 1,000 BTU per cubic foot is a common planning default, but local gas composition can shift the number.
Should I include a design margin?
Yes. A margin such as 10% accounts for startup effects, small future loads, and minor estimation error. Larger margins may be appropriate when trenching is difficult, but excessive margin can increase cost unnecessarily.
Why does propane use a table instead of the equation?
Low-pressure propane systems are often sized from code capacity tables for specific tubing types and pressure drops. The calculator selects the next longer table length to stay conservative and then chooses the smallest tubing that meets demand.
Can I rely on this result for installation?
No. Treat it as a planning estimate. Final sizing must follow your local code, material listings, regulator specifications, and inspection requirements. Always have a qualified gas professional verify the design before installation.