Automatic vent dampers:

Here we explain Automatic flue vent dampers, what they are, how they work, and why they can save money on heating bills. This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs.

We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

Automatic Vent Dampers on Heating Equipment Flues

Heating costs can be reduced by any measure that makes sure that as much as possible of the warmth produced by burning a heating fuel (such as natural gas) is sent into the occupied space rather than lost elsewhere.

[Click to enlarge any image]

An automatic vent damper, such as illustrated in Carson Dunlop Associates' sketch here and in our photograph just below, reduces heat loss in buildings where gas-fired heaters are installed.

When the heater is off the electric motor turns the vent damper to the "closed" position so that heat is not lost from the boiler nor the building by natural convection.

When the heater is about to turn on, before the burner is ignited the automatic vent damper motor opens the vent so that combustion gases can flow freely through the flue vent connector and out of the building's chimney.

Don't confuse an automatic flue vent damper with two other "damper" devices: a heating system automatic duct damper or a duct fire damper.

 

Exactly what is an automatic flue damper?

An automatic flue damper is a device which closes the heating flue when the furnace or boiler is "off" so that we won't continue to lose building heat up the chimney - it's a device to reduce heating costs and save on heating oil consumption.

At left we show an automatic flue damper installed on a gas-fired heating boiler in Two Harbors, Minnesota. This is a Weil-McLain automatic vent damper model RGP-KSF / RVGP-KS. For this model the company specifies:

• Damper must be in the open position when the burner fires
• Fire clearance: 6-inches from combustibles
• Complies with ANSI Z21.66 1994, electrically-operated flue vent damper devicve designed for gas fired heating applian ces

When the heating system has turned off at the end of an "on" cycle of burning fuel, the automatic flue damper electric (see sketch above and photo at left) motor turns a baffle inside of the flue vent connector pipe to a position "across" the pipe so that the airflow inside the pipe is blocked or stopped.

We define and describe in more detail the differences between automatic flue dampers, barometric dampers, fire dampers, and draft inducer fans

at TYPES & MODELS of DRAFT REGULATORS

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: it is impossible to adjust burner for peak efficiency without a properly working regulator.

(Sept 10, 2011) lionel scott said:
In my years of servicing oil fired appliances the most neglected part of the heating system is the draft regulator and as your article points out it is impossible to adjust burner for peak efficiency without a properly working regulator.

Reply:

Thanks, Lionel, we agree.

Question: s-120-EDP from 120,000 btu Brand sentry Gas fired boiler vent damper vs draft hood

(Nov 28, 2014) Luis said:
i did buy a gas boiler s-120-EDP from 120,000 btu Brand sentry ,it take combustion air from the button of the boiler, it came with a electric vent damper, and do not came with the draft hood . Do i need to put a draft hood on the flue system?

Reply:

Luis

Are there installation instructions with this heater?

Check the manufacturer's specs.

But to be more specific: an electric vent damper is a completely separate device that closes off a vent to stop heat loss up the flue when the heater is not running. It does not address the draft hood requirement for the system.

Your model is a Sentry Natural Gas Water Boiler 120,000 BTU Input, 88,000 BTU Output Intermittent Ignition. Model # S-120-EDP. Most likely the draft hood is built into the boiler and is an integral part of its exhaust system. That's what you'll see in the product illustrations of the "S" boilers. But the SX boilers and some other models definitely show a separate draft hood installed.

Draft hoods on gas fired heaters are described at

DRAFT REGULATORS / HOODS GAS HEATERS

Check with Slant Fin for help if you're missing the installation specifications.

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Continue reading at BACKDRAFTING HEATING EQUIPMENT or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AUTOMATIC FIRE & SMOKE DAMPERS
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• SAFETY RECALLS CHIMNEYS VENTS HEATERS

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AUTOMATIC VENT DAMPERS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS

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