Are you familiar with how they work? If not, here’s an overview:
How Conventional Water Heaters Work
Conventional water heaters are natural draft tanks. They heat your tank inefficiently. When the burners come on, heat is produced and travels in the form of smoke. These are called the flue gases. They travel through the heat exchanger and then the heat produced is transferred to the water.
Positive vs. Negative Pressure
By the time the flue gases leave the vent, they’re hot. This is called the natural buoyancy effect. Because of this, the gases naturally rise out of the chimney. The venter motor creates positive pressure that forces the flue gases out the chimney. So, conventional heaters are more vulnerable to negative pressures. When exhaust appliances, like the exhaust range hood, bathroom exhaust fan, or dryer, are turned on in the home, this creates negative pressure.
The Dangers of Negative Pressure
Negative pressure causes a vacuum in the home, so the flue gases are not naturally vented out of the chimney. Instead, they're sucked back in and reburned by gas appliances. This causes the burners, which need heat, oxygen, and a fuel source, to be starved of oxygen (the oxygen is no longer pure because flue gases are now in the mix). This is how carbon monoxide is produced.
What Happens Next?
Carbon monoxide is then vented through the chimney again and sucked back into the home, along with the flue gases, through the draft hood area.
If there’s return air (air that circulate back to the furnace) in the room, carbon monoxide will be distributed throughout the home, which is clearly a health risk for homeowners.
Other types of water heaters, like power-vented and tankless, create positive pressure, so the likeliness of carbon monoxide being produced is much lower. If you’re worried about carbon monoxide being present in your home, you may want to consider a type of water heater that is less vulnerable to negative pressures than conventional systems.
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