Heating / August 18, 2023

3 Common Problems that Affect Gas Furnace Manifolds

Despite being one of the most heavily used home appliances when cold weather rolls around, gas furnaces hold up admirably against general wear and tear. Yet problems may still occur that compromise the ability of a furnace to adequately heat your home. A gas furnace contains numerous components, any one of which can develop a debilitating problem that will need repairs.

One vital yet overlooked component is the manifold. The manifold acts as a crucial point of connection between the gas valve and the burner assembly. If you would like to learn more about the problems that afflict manifolds, keep reading.

What Could Cause Gas Pressure to Drop?

This article outlines three symptoms of low gas pressure to your furnace you might experience as a homeowner.

  1. Incorrect Pressure
  2. Insect Infestation
  3. Corrosion

What is a gas furnace manifold?

The manifold functions as the intermediary between the furnace’s gas valve and the actual burner inside the combustion chamber. The burner consists of a series of open tubes that contain an internal nozzle known as a spud.

Natural Gas Pressure for Furnace

When it comes to heating our homes, natural gas is a popular choice for many homeowners. It is clean-burning, cost-effective, and readily available. However, maintaining the proper natural gas pressure for your furnace is crucial for ensuring optimal performance and safety. Using a gas regulator to control the gas flow is essential for regulating the inlet pressure and maintaining the right outlet pressure in the combustion chamber.

Natural gas pressure refers to the force with which gas is delivered from the main supply line to your furnace. It is important to note that there are two pressure levels to consider – the supply pressure and the working pressure. The supply pressure is the pressure of gas as it enters your home from the main line, typically regulated by the utility company. The working pressure, on the other hand, is the pressure of gas as it is delivered to your furnace, regulated by the gas valve.

Proper natural gas pressure is essential for the efficient combustion of gas within your furnace. Too low of a pressure can result in incomplete combustion, causing your furnace to run inefficiently and potentially release harmful byproducts like carbon monoxide. On the other hand, excessive pressure can put unnecessary strain on your furnace, leading to premature wear and potential safety hazards. It is important to regularly monitor the gas valve and ensure the inlet pressure is at the optimal level.

To ensure the correct natural gas pressure for your furnace, it is recommended to consult with a qualified HVAC technician. They can check the pressure levels using specialized tools such as a manometer and make any necessary adjustments to the furnace gas valve or natural gas regulator. Additionally, regular maintenance and inspection of your furnace can help identify and address any pressure-related issues before they become major problems.

In conclusion, maintaining the proper natural gas pressure for your furnace is vital for both performance and safety. With the help of a professional, you can ensure that your furnace gas valve is operating at its best, keeping your home warm and comfortable while minimizing the risk of any potential issues.

Incorrect Pressure

In order for the burner to work efficiently, the gas pressure coming from the manifold must be carefully regulated.

The ideal pressure level depends on a number of factors.

  • The fuel source plays a key role, with natural gas and propane requiring different pressures.
  • Likewise, the size and capacity of the furnace affect the necessary pressure.

Symptoms of Low Gas Pressure to Furnace

What happens when there is incorrect furnace gas pressure?

What should gas pressure be for a furnace?

A professional HVAC technician can measure and adjust the manifold pressure of your gas valve if necessary. In most cases, a gas furnace should have a manifold pressure of around 3.5 inches of water, or 3.5 WC (water column) for short. The ideal pressure setting can also be found on the rating plate

Insect Infestation

You likely only need to run your furnace 3-5 months of the year depending upon what area of San Diego you live. The rest of the time, the furnace sits idle. Unfortunately, this downtime gives unwanted pests plenty of opportunities to take up residence inside of your furnace and its components.

While birds and rodents can create problems inside your duct system, your furnace gas valve itself remains more prone to insect infestations. Should these insects build their nests inside your furnace’s manifold, the resulting debris may create problems once winter rolls around, creating blockages that negatively affect flow and pressure.

Your chances of dealing with insect problems go up if you choose to turn off your gas furnace’s pilot light in the summer. A non-functioning pilot orifice provides the perfect point of entry for unwanted critters. The gas valve for your furnace can help regulate the flow of gas in your heating system.

Keeping your pilot light on throughout the summer will cost you far less than having to have your burner assembled and manifold disassembled for a thorough cleaning.


Over time, a gas furnace manifold may develop corrosion that inhibits the proper flow of gas. Such corrosion forms naturally as the result of the combustion gas reaction, which allows water vapor to condense as the furnace cools down after a heating cycle. The gas valve plays a crucial role in regulating the flow of gas in the heating system.

Likewise, excessive soot buildup also hastens the rate of rust formation. Fortunately, in a well-maintained furnace, the manifold pressure should experience relatively little corrosion compared to other components.

Always hire a professional to inspect and tune up your system prior to each winter. The technician can remove any existing corrosion to reduce the likelihood of the problem growing out of control.

Need Your Furnace Inspected or Repaired?

The manifold plays a huge role in the overall working of your furnace. If your furnace is not acting properly and might be in need of repair, contact us or book an appointment for our specialists in San Diego to come to take a look.

Mauzy Knowledge

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