Question from Sunbury: What is a Gas Furnace Draft Hood?

As every Sunbury HVAC contractor knows, a draft hood is a necessary part of any gas burning appliance. For a gas furnace in particular, it ensures steady air flow to the burners in order to avoid flares or the pilot light being put out by fluctuations in temperature and air flow.

What the Draft Hood Does

The draft will change in the chimney as exhaust vents towards it – especially when going from cold air to hot. A draft hood is placed above the upper most part of the gas furnace to draw air into the chimney and makes it possible to draw more or less air through the chimney as necessary to create a constant flow.

This makes it possible for the burner to enjoy consistent air flow without any wind gusts or sudden temperature spikes or drops. Hot air, if not put through a draft hood, would create a strong air flow through the burners.

A draft hood cools the air as it is released by the burners from 500 degrees Fahrenheit to between 300 and 350 degrees Fahrenheit. The cooling needs to be carefully calibrated to avoid condensation build up in the chimney however – a problem that occurs when the temperature gets too low.

Maintaining Pressure

The draft hood is a part of a larger system designed to maintain air flow to the chimney. For every cubic foot of gas burned, the furnace needs to have 15 cubic feet of air for combustion and another 15 cubic feet of air for dilution. A draft hood and the rest of the ventilation system make it possible to put a furnace that has many thousands of BTUs in the basement of your home and still supply it with enough air to burn gas and dilute the exhaust before it enters the chimney.

For all of these reasons, if you see your pilot light flickering irregularly, notice a backflow of exhaust, or a burning smell in your furnace room, it’s important to call a Sunbury professional who can inspect and repair the problem before it becomes any worse. Not only can gas burner exhaust contain high levels of carbon monoxide, it can be bad for the device and the chimney if it doesn’t vent properly.