What Size Gas Line For Garage Heater? Answered!


I understand that choosing the right gas line size for your garage heater can be overwhelming. It’s important to ensure your safety and the optimal functioning of your heater. 

So, what size gas line for a garage heater do you need exactly?

You need a gas line with ½ inch diameter if your garage is attached to your home and  your heater capacity is 35,000BTU. If the heater capacity is more than 35,000 BTU and less than 80,000BTU you need a ¾ inch diameter gas pipe. For garages detached from the home you will need a longer pipe with a greater internal diameter.

Is that all you need to know about the size of the gas line you need? Not really. So let’s dig in and find out!

What Size Gas Line for Garage Heater Should I Get? An In-Depth Answer.

This process involves math. Go to the subsequent section for an easier generic answer.

what size gas line for garage heaterSource: Youtube

Step 1: Determine The BTU of the Garage Heater

To determine the BTU of the garage heater follow this process:

  1. Determine the volume of the garage using a measuring tape in feet. Simply measure the length, breadth and width of the garage and multiply them.
  2. Multiply the obtained garage volume with 0.133.
  3. Multiply that with the desired temperature increase

Example: A 4,000 cubic feet garage will require a 30,000 BTU heater for a 56 F increase.

Step 2: Convert the BTU to CFH

CFH or Cubic Feet Hour is a measurement of the gas flow rate. BTU or British Thermal Unit, on the other hand, is a measure of energy. BTU can be converted to CFH using the heating value of the gas being used.

1 CFH of natural gas typically generates 1037 BTU of energy. So, to convert the BTU to CFG, simply divide it by 1037. In the previous example, a 30,000 BTU heater will require 28.92 CFH. This is the capacity of the natural gas pipe.

Step 3: Determine the length of the gas pipe 

Take a measuring tape and determine the distance between the gas source and the heater in the garage. This is the length of the gas pipe that you need. As the length increases the diameter would need to be increased to accommodate for the increased pressure drop.

Step 4: Determine the inside diameter of the pipe 

After determining the length of the gas pipe you now need to determine the inside diameter of the pipe. You can easily do this using the capacity of the natural gas pipe determined in Step 2. 

For this purpose you need the Spitzglass formula. Here is the Spitzglass formula that you need:

q = 3550 k ( H / (L x SG))1/2


q = the capacity of the natural gas pipeline. The unit for this is CFH

k = [d5 / (1 + 3.6 / d + 0.03 d)]1/2

d = internal diameter of the pipe in inches

L = length of the pipe in feet

SG = Specific gravity of natural gas. The specific gravity of natural gas can range from 0.5 to1. It is typically considered around 0.6.

H = pressure drop. It is calculated in inches of water column. Its value will usually be around 0.5 inches.

So in our previous example, the value of q will be 28.92 CFH for the 30,000 BTU garage heater. let the pressure drop be 0.5 inches and the specific gravity be 0.6. So if the length of the pipe is assumed to be 100 ft the value of d will be 0.567 inches. 

Doing back calculation may be easier for you in this case. You could also take help from an online calculator for internal diameter calculation of the natural gas pipe.

What Size Gas Line for Garage Heater Should I Get? In Short 

Follow these steps to quickly determine what the size of the gas line for your garage heater should be:

Step 1: Determine The BTU of The Garage Heater

The size of the gas line will depend on the garage heater capacity. Once you know the BTU capacity, you can easily determine the required gas line size. This is done by multiplying the garage volume with 0.133 and the needed temperature increase. 

A typical one car will need about a 10,000 BTU garage heater. But if the garage has an insulated ceiling less heating capacity will be needed.

Step 2: Garage: Attached Or Detached From Home

The size of the gas line can vary based on whether your garage is attached or detached from your home. If your garage is far from your home, the length of the gas line will be significantly longer than 100 feet. 

However, if it’s closely attached to your home, the length may be less than 100 feet.

Step 3: Determine The Length Of Your Gas Pipeline

The diameter of your gas line for your garage heater depends on the BTU capacity and the length of the gas line. For gas lines with a capacity of more than 35,000 BTU and a length of 10 to 20 feet, a 1/2 inch diameter gas line will suffice. 

However, if the gas line capacity > 80,000 BTU, and your garage is separate from your home, a longer gas line is required. In this case, a 3/4 inch diameter gas line should be used, even if the BTU capacity is close to 80,000.

Step 4: Selecting The Ideal Pipe Size

After considering all the relevant factors, it’s time to determine the appropriate size of the gas line for your garage heater. If your garage is close to your home and the gas line won’t be very long use a 1/2 inch pipe. But it should be able to handle up to 35,000 BTU. For higher BTU capacities, a 3/4 inch pipe will be more suitable.

However, if your garage is located far away from your home, you’ll need a longer gas line. In this case, a 3/4 inch pipe with a larger diameter will be necessary. The good news is that this size of gas line can handle both high and low BTU capacities. 

But if your garage is over a buried power line you should take some precautions when installing the gas line.


Can You Go From A Smaller Gas Pipe To A Larger One?

Yes, you can go from a smaller gas pipe to a larger one. This will cause no problem with the gas flow. But the larger pipe will cost more, require adapters and will need more time for the installation.

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