Sealed Combustion Heaters: What are they and do I want one?

December 19, 2016

One of the common phrases used today in the residential heating industry is ‘sealed combustion.’ It is relevant to the discussion of forced air furnaces, hot water boilers, space heaters and even water heaters–but what does the term mean and how does it relate to how we heat our homes and our hot water?

Sealed Combustion Defined

The simple definition of a sealed combustion heater is that the equipment uses only outside air for the fuel-burning (combustion) process that takes place in the equipment. A pipe is used to bring outside air into the gas burning appliance, and another pipe sends the exhaust products to the outdoors. What makes this unique and important is that the gas burning process is sealed and isolated from the indoor air of your home.

Sealed combustion heater mechanic

Advantages of Sealed Combustion Equipment

Sealed combustion equipment offers you the following advantages:

  • More efficient than similarly designed but non-sealed equipment, because it does not take air from inside the house, which has already been heated, to use in the burning process. Therefore, heated indoor air is not pulled into the unit and then lost to the outdoors.
  • Quieter operation than non-sealed equipment because the burners, and often the system’s exhaust fan, are located in a tightly sealed compartment inside the equipment. In the case of non-sealed combustion equipment, these components are open to the surrounding area, making the operating noise more noticeable.
  • Sealed combustion equipment is also safer, because this type of design isolates unhealthy exhaust gas products from your indoor breathing air. It would take a breach of normal operating conditions for combustion products to enter into your indoor air. Regular annual servicing of your system helps ensure that the system continues to work as designed!

Where Are Sealed Combustion Designs Used?

Sealed combustion designs are available in most current 90% AFUE efficient (or higher) forced air furnaces, as well as a variety of central hot water heat boilers, wall-mounted gas heaters, specialty tank type water heaters, and also a variety of tankless water heaters. In many cases, the exhaust and fresh air pipes are terminated through the sidewall of your home.

Sealed Combustion venting design

What Does Sealed Venting Look Like?

The type and orientation of the pipes used for the exhaust and air intake is varied. Sealed combustion furnaces most often employ two separate schedule 40 PVC pipes, terminated through the sidewall or roof of the home, one exhausting warm flue gases to the outdoors and the other bringing fresh outside air into the furnace for combustion. The pipes typically have a two or three inch inside diameter, and are sometimes combined at the wall or roof termination into a concentric, pipe-in-pipe design for cosmetic purposes, so that there is only one clean penetration to the outdoors.

In some cases, you may instead see a combination of stainless steel exhaust pipe and PVC combustion air piping. In other cases, and common with many high efficiency water heaters, the concentric design described above is used from start to finish. Regardless of how it’s accomplished, the vent system must be rated to handle the equipment’s maximum exhaust temperature and also allow adequate outdoor air into the heater for clean, proper fuel burning.

There are very specific requirements for how long the vent pipes can run, how many elbows can be used, and at what angles the pipes can be routed. Each manufacturer provides detailed venting parameters for their equipment in their printed installation instructions. Sealed combustion equipment should be installed by a licensed professional, and requires a permit from the local building authority. The permit provides for an onsite final inspection to make sure the work was performed properly, and to ensure homeowner safely.

Outdoor vent terminationIf you are in the market for a new furnace or boiler, or are considering upgrading your water heater or adding a space heater, we recommend that you consider sealed combustion equipment.

In the Denver and Boulder, Colorado area, you can count on Save Home Heat Company to make heating recommendations that make the most sense for your home and your family, now and in the future. Our highly skilled and experienced technicians and estimators will be glad to discuss options in a low pressure fashion, and let you know if a sealed combustion system makes sense for your unique situation!