High Efficiency Furnace Venting: What You Need To Know

Presidential Heating & Air Conditioning

Gaithersburg HVAC Contractors

a filter being replaced for a furnace that has a high efficiency furnace venting systemIf you are thinking of installing a natural gas furnace in your new home or replacing an existing system with natural gas heat, be aware of the importance of high efficiency furnace venting. The process of burning natural gas creates combustion gases as byproducts. For health and safety reasons, these combustion gases must be expelled through the furnace ventilation system out of your home.

A conventional natural gas furnace will vent the dangerous combustion gases through a simple vertical exhaust system that is attached to the furnace. The exhaust system typically uses metal venting, often routed into a chimney stack, to exhaust the combustion gases created in the furnace fire chamber. However, these combustion gases contain residual heat that is lost through the ventilation. You can capture that heat with a high efficiency condensing furnace.

A high efficiency condensing furnace can achieve efficiency ratings of 90 or above. It uses a venting system to extract that heat before venting. What is vented is a residual corrosive condensate of water and carbon dioxide. This residual liquid is highly acidic. It will ruin the standard venting equipment that is used in conventional gas furnace ventilation systems.

To avoid this problem, high efficiency furnace venting requires the use of PVC pipes instead of metal pipes to remove the acidic condensate from your home. These PVC pipes are connected to the furnace and expelled outside. This high efficiency venting system must be installed when you install the new furnace. The PVC pipes are used for air intake, exhaust gas, and to remove the corrosive condensation resulting from the combustion process.

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Other Aspects of High Efficiency Furnace Venting

There are several other important aspects of high efficiency furnace venting. Most specifically:

Electronic Ignition

A high efficiency condensing furnace has an electronic ignition mechanism. It is a hot surface ignition system that uses an electronically controlled resistance heating element, similar to a light bulb filament. The hot surface of the heating element ignites the gas burner. It provides better performance and higher safety than a pilot light. It also provides energy savings due to its superior operating efficiency.

Special Furnace Venting and Drainage

high efficiency furnace venting installed by a Maryland HVAC contractorAs explained above, a high-efficiency condensing furnace has special venting and condensate drainage requirements. It also has special heat exchanger technology that is able to extract heat from the fuel combustion process for a longer period of time. It extracts heat even until the point where the combustion exhaust gases have cooled down and condensed. The resulting condensation drips out of the furnace's heat exchanger and runs into a floor drain or special catch basin. The low-temperature residual flue gases vent outside through special plastic pipes.

Sidewall Venting

When your new high-efficiency condensing furnace is installed, your contractor should take extra precautions to make sure all ventilation systems are properly placed and working correctly. One of the most important safety features of gas-condensing systems is sidewall venting.

Proper sidewall venting requires installing separate vent pipes horizontally so that they vent to the outdoors through a wall of your home. These ventilation pipes should be isolated from the furnace combustion chamber and made airtight to eliminate the possibility of combustion gas leakage. They should be constructed so that any condensate in the pipes drains backward without freezing and drains into the floor drain or catch basin.

A high efficiency condensing furnace, if not properly ventilated, can present two safety hazards. First, the gas byproducts can contain residual carbon monoxide that could leak back into your home unless the ventilation pipes are airtight. Second, improperly venting the exhaust through a chimney (as frequently done with conventional gas furnace systems) can damage chimneys and chimney liners if it accumulates and freezes. Also, the acidic elements in the exhaust can damage unprotected chimney bricks and mortar. For these reasons, exhaust from a condensing furnace should never be vented through a standard chimney.

Two Heat Exchangers

High efficiency furnace venting uses two heat exchangers. (Conventional furnaces use only one.) They use a two-stage process. In the first stage, gas is burned to heat the first heat exchanger. After the first heat exchanger is heated, the second stage begins. In the second stage, the secondary heat exchanger extracts heat out of the hot exhaust gasses. This heat extraction process cools the exhaust gasses to the point that the water vapor in the exhaust gas condenses into water. Any resulting gas byproducts are cool enough to vent them outside through a PVC pipe. The condensed water is run to a floor drain.

Indoor Air Quality Guide

Is Your Furnace Causing Trouble?

Take the Quiz

Is Your Furnace Causing Trouble?

Take the Quiz


an air filter being replaced for a high efficiency condensing furnace

Change The Air Filters Regularly

Change the furnace filters at least every three months. If you have pets, you should do it more frequently. A simple $1 fiberglass filter will protect the blower and blower motor. You can also buy special more expensive filters to filter out smaller particles. Be sure you check the owner’s manual for the manufacturer's recommendations. The more powerful filters can put undue strain on your furnace by restricting airflow too much. Replace the return air filters. If you have a permanent-type filter, follow your manufacturer’s recommendations for cleaning it to remove dust and debris.

Make Sure Ventilation Pipes And Condensation Drains Are Unobstructed.

Keep the vent and drain pipes open. Check them regularly and remove any obstructions.

Schedule Regular Tune-ups With A Professional HVAC Contractor

A high efficiency condensate furnace can save you lots of money on your heating bills. However, you need to make sure the system is operating properly. If the condensate from a high efficiency furnace leaks out of the PVC pipes, or if the pipes are not draining the condensate correctly, you could experience damage to your home and you may not be aware of it until the damage becomes significant. A professional HVAC technician will ensure that your venting pipes are tightly secured and properly installed. The technician will also inspect your system and take care of any potential or minor problems before they become significant.

Contact A Professional HVAC Contractor For More Information About Furnace Venting

Before you select a new furnace system, consider a high efficiency condensate furnace. Contact an experienced HVAC contractor for more information about high efficiency furnace venting as well as furnace installation, repair, or maintenance.

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