Any appliance or mechanical system that uses natural gas, propane, oil, or wood, creates combustion gases. Properly sealed systems pose no risk of combustion spillage, but systems that are not sealed pose a risk of combustion spillage into the home. Combustion gases can also come from an attached garage, especially if poorly constructed or improperly sealed. These gases pose a threat to the occupants and to anyone working in the home.

Mechanical Systems can cause pressurization or depressurization in a house while operating. By mechanically moving air around a house you effectively move moisture, heat and sound as well. Exhausting air may create a back drafting situation for fuel fired appliances

Concerns

Several types of by-products are of major concern:

• Nitrogen Dioxide
  
• Carbon Monoxide
• Organic Pyrolysis products from incomplete combustion

Nitrogen Dioxide is a product of normal combustion and can be introduced into the indoor air stream through unvented gas stoves and heaters. Significant amounts can be released into the air simply through the operation of pilot lights on gas appliances. For a safer home, use appliances with electronic ignition, not a pilot light and ensure the appliance is properly vented to the outdoors.

Carbon Monoxide is the product of incomplete combustion and is addressed by following standard safety procedures in installing and operating combustion appliances. Carbon monoxide poisoning occurs after breathing in too much carbon monoxide (CO).

Symptoms of mild poisoning include:

• Light-headedness
• Confusion
• Headache
• Feeling like the world is spinning
• Flu-like effects

Larger exposures can lead to acute poisoning. Symptoms of acute poisoning include:

• Toxicity of the central nervous system and heart
• In some cases - death

Combustion Spillage

Signs of Combustion Spillage include:

• Discolouration around burner air inlet, draft hood or dampers
• Darkened paint on heating appliance
• Melted plastic grommets around cold and hot water pipes on top of water heater; melted pipe insulation
• Water stains, rusted connectors to chimney, dripping on top of water heater or on top of baffle inside air inlet of furnace
• Smoke stains on front of brick fireplace

Factors that Cause Combustion Spillage:

• Where exhaust appliances induce a negative pressure on the house
• Where wind creates a negative pressure in the area of the house where a spillage susceptible appliance is located
• Where a house is relatively air tight and no combustion or make-up air is supplied to the spillage susceptible appliance

How to Avoid or Reduce Likelihood of Combustion Spillage

• Avoid using spillage-susceptible appliances in the house
• Ensure balanced ventilation system
• Provide exterior combustion air
• Avoid high flow exhaust equipment

To Prevent or Reduce Combustion Spillage:

• Use appliances with electronic ignition
• Ensure the appliance is properly vented to the outdoors
• Supply combustion air to fuel fired appliances
• Provide make-up air for appliances with no combustion air supply

Smoke/CO Detectors - NBC 9.32.3.9

• CO detectors must be installed if:
  • There is a fuel burning appliance in the dwelling unit
  • Or, the dwelling unit shares a wall, floor or ceiling with a garage
• CO detectors to be installed outside bedroom doors within 5 m, or inside each bedroom

Natural Air Supply / Exhaust-Only Systems

Many mechanical systems such as furnaces and wood stoves rely on natural air to use as supply air. A system like this will use the air in the home for combustion, which leads to outside air being sucked into the home, and sometimes back down the flue of the system, causing combustion spillage.

Whenever there is a negative pressure inside a house, there is a risk that combustion gases from naturally vented/aspirated appliances can be drawn into the living space rather than out the chimney or exhaust.

If an upgrade makes the house more air tight, then make-up air or a ventilation system, may need to be installed if there is no ventilation system.

Things to Consider….

When working in a home with active mechanical systems, consider if they have a balanced air supply and exhaust, are sealed properly, or are they naturally aspirated (no supply).

Consider the effects of the renovation on the home:

• What other work is being performed on the house while I am insulating?
• Will it effect my insulating or sealing job?
• Will it effect how the air in the home flows?
• Is the house going to be more air tight?