Cold drafts at home made combustion air supply (C) InspectApedia DA Power Vent Openings & Louvers for Combustion Air
Safety Features on Powered Combustion Air Vents Avoid Combustion Air Problems

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Combustion air openings operated by power louvers or power vent opening mechanisms:

This article describes the requirements for safe operation & control of heating systems whose combustion air is provided by a powerd automatically-opening and closing louver or vent system. The article continues with photographs and comments on an un-safe home-made vent control intended to avoid cold drafts at the combustion air inlet.

This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters. These articles answer most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs.

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Combustion Air Inlet by Automatically Operated Louvers or Dampers

Backpressure sooting at an oil fired furnace (C) Daniel FriedmanWatch out: inadequate combustion air not only causes improper and wasteful operation of heating equipment it can also produce fatal carbon monoxide gas hazards indoors. The quantity of combustion air needed depends on the fuel type, the input BTUh rating of the heating equipment, and additional air needed to assure effective exhaust draft to carry combustion products safely out of the building.

Question: louvered combustion air opening operating sequence

2016/06/22 Keith preddie said:

Can anyone go through the control sequence between louvered openings and the gas fired equipment?


Keith, If I understand the question

  1. Thermostat calls for heat
  2. Motor-operated louvers open to supply combustion air to the bas burner
  3. An end switch should be present that does not allow the burner to turn on until the louvers are fully open (assuring that safe combustion air is provided)
  4. Burner operates
  5. Thermostat is satisfied
  6. Burner turns off
  7. Louvers close

Watch out: automatically operated combustion air louvers or dampers must meet specific safety requirements for wiring and burner control to assure that the burner doesn't fire if the air inlet is not open. If the louvered opening does not open fully as required before the burner starts, fatal carbon monoxide gas could be produced. And if the louvered opening doesn't close when it should cold or even freezing air can cause building damage or even loss of heat.

Air opening size for any combustion air supply inlet should meet the BTUH requirements of the equipment and follow the requirements of the

For gas equipment the full name of the standard is NFPA 54/ ANSI Z223.1, National Fuel Gas Code, for gas-fired boilers

Or the Standard for the Installation of Oil Burning Equipment, NFPA 31.

Fans supplying combustion air must be interlocked with the boiler as should be power-louvered controls over combustion air openings.

Also see ASME CSD-1 2009, Safety Controls and Devices for Automatically Fired Boilers
There paragraph CG-260, Combustion Air includes

(b) Louvers and grilles shall be fixed in the open position or interlocked with the equipment so that they are opened automatically during equipment operation. The interlock shall be placed on the driven member.

See the model code specifications for combustion air inlets cited at COMBUSTION AIR for POWER BURNERS

Combustion Air Inlets vs Cold Drafts

Reader Question: fixing cold drafts coming in at the natural gas furnace combustion air inlet set up by my contractor

Cold drafts at home made combustion air supply (C) InspectApedia DA

[Click to enlarge any image]

2016/04/02 Doug said:

I have a NG forced air furnace and a NG fireplace in my 2004 built home in the WNY area. I have a independent draft regulator venting into my basement. I do not understand why I need this? My understanding at the time by the home builder was that he builds "airtight" homes and that's why I need it.

Fact is my house is far from "airtight", and this vent is on the windy side of my home and this vent allows a steady stream of cold air into my basement making it quite cold threw the winter months. I am planning a basement finishing project know and want to eliminate the source of the cold air. Just curious what the ramifications may be. I do have photos, but this comment section doesn't seem to allow :(

This question was posted originally at DRAFT REGULATOR, DAMPER, BOOSTER

Reply: home made combustion air supply systems may be unsafe


If a gas-fired heating appliance does not have adequate combustion air it can produce fatal levels of carbon monoxide. The draft-hood on your natural gas furnace regulates the draft but does not provide combustion air to the furnace.

Your heating service tech can check your system operation, location, burner adjustment, flue draft, size of the area where it's located, and similar specs and can compare those with the manufacturer's requirements to be sure there is adequate combustion air.

I agree that if the area where the furnace is located is big enough or receives enough natural ventilation and combustion air, you may not need the extra air source.

Cold drafts at home made combustion air supply (C) InspectApedia DA

See found by searching for COMBUSTION AIR REQUIREMENTS

You are welcome to send us photos via the page bottom CONTACT link.

Reader followup:

Thanks for the valuable information. I did send my photos per your link for your edification.



This looks like a home-made jury-rigged combustion air inlet for heating equipment. It looks as if there is a dryer vent, flex duct, and a barometric damper used (backwards) - I can't understand how that setup would work. And even what's there is not correctly installed: both in application, sizing, and installation (out of level).

Cold drafts at home made combustion air supply (C) InspectApedia DA

Usually a Field Controls draft regulator like the one in your photos vents OUT through its opening face, not in to the room where your set-up is shown.

You'll want to see the article I cited above and also COMBUSTION AIR for TIGHT BUILDINGS

One can't guess at what your equipment needs from just those photos (the articles explain the basics of how to figure that out). But it seems unlikely that a clothes dryer vent sized intake provides a meaningful amount of combustion air anyway.

If your heating appliances do not have enough combustion air without ducting in outdoor air, there are systems that will duct the air right to each burner where it's needed, avoiding creating a chilly draft across the floor of the same spaces.

Watch out: inadequate combustion air supply to gas fired heating appliances risks fatal carbon monoxide poisoning.


Continue reading at COMBUSTION AIR SAFETY CHECK or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



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