🎸 The song, “Rock The Casbah”, by The Clash, was a popular hit from the 1980's. Punk rock at its finest. A song widely interpreted as a critique of oppressive regimes and a celebration of freedom and expression. But, what the heck do we mean by don’t rock the “CAZ”-bah?
Known as the Combustion Appliance Zone, the CAZ is very important with regard to the safety of your home. The CAZ does become a bit more relevant depending on the style of your gas-fired mechanical systems. We’ll comment on that shortly. First, let’s understand what the CAZ is and why it’s important.
What Is the CAZ?
The Combustion Appliance Zone (CAZ) refers to any area in a home that contains combustion appliances, such as:
- Gas furnaces
- Water heaters
- Boilers
- Wood or gas stoves
- Fireplaces
- Gas Dryers
This zone is where combustion occurs to create heat, and where the byproducts (like carbon monoxide) must be safely vented out of the home.
Why the CAZ Is So Important
Improperly functioning combustion appliances or poor ventilation in the CAZ can lead to serious health and safety hazards. Here’s why the CAZ matters:
1. Carbon Monoxide Risk
If combustion gases are not vented properly, deadly carbon monoxide (CO) can backdraft into the living space. Testing the CAZ ensures CO stays outside where it belongs.
2. Backdrafting Hazards
A depressurized CAZ can cause combustion gases to flow back into the home instead of up the flue. Weatherization activities (like tightening the building envelope) can unintentionally increase this risk.
3. Draft Pressure Testing
Part of CAZ testing includes measuring draft pressure in the flue during appliance operation. This helps confirm that exhaust gases are moving safely up and out.
4. Spillage Testing
Inspectors also test whether gases are spilling out of the appliance when it runs, especially during worst-case depressurization conditions (all exhaust fans running, doors closed, etc.).
To summarize in simple terms, the CAZ absolutely needs an adequate amount of air for proper combustion, as well as effective venting for the gas burning byproducts.
As I mentioned earlier, there is a difference in how mechanical systems vent out gases. Your furnace or water heater may atmospherically/naturally draft (no fan assistance), or have mechanical assistance, which means a fan is forcing the gas up and out the flue pipe. An atmospherically drafting system relies much more heavily on proper air pressure in the CAZ for safe operation.
What Happens During a CAZ Test?
A qualified technician will:
Turn on all exhaust fans and simulate “worst-case” conditions
Measure room pressures with manometers
Test appliance venting and CO levels
Determine if the CAZ is safe, marginal, or unsafe
The CAZ is where your home breathes fire, and it must be carefully managed.
Ensuring this zone is safe is not just a code requirement; it's a life-saving measure.
If you're working with an energy auditor or weatherization team, make sure CAZ testing is on the checklist...because efficiency and safety should go hand-in-hand.
And one last thing...be sure you have an operational carbon monoxide detector in your CAZ. 👍
- The Weatherized Brat 🛠
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