Proper Gas Piping to a Rooftop HVAC

Redundant Valves

• Gas valves are one of the key parts of the HVAC system. They regulate when the rooftop units receive gas and how much gas flows into the burners. According to most manufacturer installation instructions, the gas valves should be in a redundant configuration. This means that at least two valves should be used on the same line leading up to the roof. This allows multiple options for shutting down the gas line in emergencies from either end of the HVAC system, increasing safety.

Entering Unit and Burners

• Gas piping leading up to a rooftop furnace or heater should enter the unit through only one location, on one horizontal side of the furnace. Branching gas lines are a bad idea, even if the gas needs to access multiple burners. The more gas inlet holes in the heating unit, the greater chance for leaks, corrosion and gas line damage. Installation requirements force simplicity by requiring only one entry point on one side of the rooftop unit.

Pressure

• Gas pressure is a key concern when piping fuel gas to furnace. The longer the pipes, the more the pressure drops and rooftop HVAC systems require lengthy piping from the main line. For this reason, contractors and installers use charts that show how large pipes need to be based on pressure drop information. Pipe that needs to go 50 feet to reach a rooftop HVAC unit may need to be 2 inches in diameter, but gas pipe that needs to be laid for 100 feet may require a smaller size to keep gas pressure stronger and more stable. Altitude also has an effect on pressure drop, so separate calculations may need to be factored in based on the elevation of the location.

Decentralized Controls

• Rooftop HVAC units can be difficult to access for maintenance or repairs. To make work on these systems more simple, another installation requirement is often a decentralized control panel located on the unit itself. This allows for more detailed work and control when working up on the roof while also increasing safety parameters in case of electrical failure.