Here are the steps to verifying correct gas pressure during start-up.

Sizing Gas Line

1. Select correct size piping for each unit to assure there is enough volume of gas to maintain correct gas pressure during operation of burners. 

Requirements for Gas piping

2. Requirements for Gas Heat Note: The unit gas train and optional through-the-base gas shut-off valve are rated at 1/2 PSIG maximum. A pressure reducing regulator is recommended to prevent this maximum from being exceeded. These components must be isolated during field gas piping test that exceed 1/2 PSIG. It is recommended that the field piping be capped prior to the unit gas train or optional through-the-base gas shut-off valve if present. 

• Gas supply line properly sized and connected to the unit gas train. 

• All gas piping joints properly sealed. 

Leak testing and inlet gas pressure requirements

3. Use caution when performing gas line testing to prevent equipment and gas valve damage. Follow guidelines below. After leak test is completed gas pressure will need to be verified with a Manometer. 

• Gas piping leak checked with a soap solution. If piping connections to the unit are complete, do not pressurize piping in excess of 0.50 psig or 14-inch W.C. to prevent component failure. 

• Drip leg Installed in the gas piping near the unit.

• Minimum gas supply pressure should be NAT 4.5-inch W.C. / LP 11-inch W.C.

• Maximum gas supply pressure must not exceed NAT 14.0-inch W.C. / LP 14-inch W.C.

Recommended Inlet and Manifold Gas pressure for operation

4. Locate the pressure settings for the gas on the nameplate or in the IOM of the unit. 

Here is an example of the information found the nameplate for a Two Stage Natural Gas unit. 

Setting the correct Manifold Pressure

5. To make the recommended pressure settings for Single stage or Two stage gas valves you will need to connect a Manometer to the INLET tap for incoming gas pressure setting. Once the incoming gas pressure is set correctly shut the gas off and remove Manometer and reinstall the INLET plug with pipe sealant. After the plug is installed, turn the gas valve back on and leak test tap to make sure it is not leaking.  

  Failure to install the tap after completion of testing correctly can result in a Fire Hazard. 

6. Once the INLET has been set correctly and the plug reinstalled, the Manifold pressure can now be set. Locate the plug for the OUTLET located on the gas valve side for the manifold and connect the Manometer hose and fitting for setting the pressure. 

How to set the OUTLET gas pressure for single stage and two stage equipment.

7. To set the gas pressure on the manifold, locate the Regulator cap cover screws or screws. Remove the cap or caps and insert a flat head screwdriver in the slot of the plastic adjustment screw to make adjustments to meet the correct gas pressure recommended. Make adjustments to Single stage and Two stage gas valves based on information provided with the nameplate and IOM. Place the unit into 1st stage of heat and set Low-fire gas pressure. For single stage gas valves there is only one setting with first stage heat call. Once Low-fire is set place the unit into 2nd stage of heat and set the High-fire pressure. After both stages are set, reinstall the regulator caps. Remove the heat call and shut gas valve off. Remove the Manometer and install the plug 

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.