Sealed-Combustion Equipment Located in Conditioned Space

Sealed-Combustion Equipment Located in Conditioned Space


There are concerns that exhaust vents (bathroom, kitchen, etc.) can depressurize a tight home and cause by-products of combustion from appliances to be drawn into the home. If installing combustion space and water heating appliances, minimize the back drafting potential by choosing direct vent (sealed combustion) or mechanical/induced draft (power-vented) equipment. All space and water heating appliances must meet these criteria to receive points.

Note: Points can be obtained for this guideline by mixing equipment types. For instance, direct vent space heating equipment and an induced draft water heater can be installed and receive credit.

Additional Information/How to Implement

Combustion appliance manufacturers offer equipment with various means of exhausting by-products:

  1. Unvented equipment (a.k.a., ventless, vent-free) where by-products are exhausted into the home;
  2. Natural draft equipment (a.k.a., atmospherically vented) where environmental pressure and temperature differences cause by-products to be drawn up a chimney which is directly connected to the equipment;
  3. Mechanical draft equipment (a.k.a., induced draft, power vented) where by-products are exhausted through a vent due to pressure differences created by a fan, blower, or ejector located in the vent, or
  4. Direct vent equipment where all combustion takes place in a sealed chamber. Combustion air is drawn directly from the outdoors into the chamber. Products of combustion are then vented directly outdoors. Direct vent space heating equipment also has an energy benefit as compared to natural draft or mechanical draft equipment. The Annual Fuel Utilization Efficiency (AFUE) of direct vent equipment is typically above 85%.

Direct vent water heaters remain quite expensive. Mechanically vented or electric water heaters may be the most practical option for many builders wishing to comply with this guideline. Some local codes may require an outdoor source of combustion air for mechanical draft equipment.

An alternative to direct vent equipment includes isolating combustion equipment from the conditioned space such as constructing a combustion closet.

Diagram of house venting


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