Clogged duct?

Old 08-30-03, 09:09 PM
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Clogged duct?

Hi there,

I've just installed a new gas water heater but I'm suspicious that the vent duct in the ceiling might be clogged. I tested it with a piece of burning paper to see if smoke gets sucked in and it didn't. I did the same thing with the duct for the dryer which is located a few inches above floor and it, too, didn't seem to be drawing any air in.

Are they connected together behind the wall or are they two separated ducts that are terminated in the roof?

Shouldn't I be able to feel a fairly strong draft with my fingers placed over the duct opening? I've read that fumes from the burning gas in water heater are actually very harmful. But how do I make sure that fumes are safely sucked in and are not escaping out and filling the small closet?

Old 08-31-03, 09:03 AM
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Hello Eko. Welcome to my Gas Appliances forum and our Do-It-Yourself Web Site.

Bear with me, I'm thinking through the testing method and attempting to put it into words. Not always an easy task nor a brief method and to do so properly.

It is imperative {highly important} to note details and procdures in exactly the correct testing method. The description below is the first time ever attempted in this forum. It is highly descriptive and detailed.

Often repeated words and phrases used in several ways for clearity must be used. Many other members are also reading this forum and this topic. Therefore and as a result of, it is incumbent upon myself as a professional to be very clear, concise and well understood in & on matters such as this.

In most cases it is easier to print this information. The printer friendly version option is below. Using it may be helpful.

A venting system not functioning correctly can be highly dangerous. Fumes can & will contain carbon monoxides. The amounts vary. None is exceptable in the living envirnoment once the vent pipe heats up.

If there is suspicions of fumes entering the living area as a result of a blocked and or restricted venting system, it is highly recommended & suggested to have a professional test the system.

Most gas companies, natural or propane, do this simple test to ensure public safety. As do plumbers & installers of water heaters and room/house heating agents, etc.

In order for drafting to take place, the venting system has to have hot gases attempting to escape up the vent pipe. The roof top vent cap does not allow much outside air to enter down the vent pipe.

If the roof top vent cap on the outside rooftop vent pipe is installed correctly, by this I mean not pushed down too much on the exposed pipe end, the cap will do it's job.

Allow hot fumes and gases to escape out to the outside but not allow outside air forced by winds to backflow down the vent pipe.

The down draft diverter cap installed correctly on the top of the water heater will set up on it's legs. The vent pipe onto it. The open space just beneath the cap and that above the water heaters built in flue pipe, is the space where inside air enters to the vent pipe to help dilute the hot escaping gases and fumes.

Once the water heater, a non power vented type, is warmed up after being on for 5 minutes max time, that space should be drawing in and upwards air very close to it.

The test to verify if inside air is being drawn upwards into the space between the water heaters flue and the down drafters cap, is to strick a stick match. Once a flame is established on the match, put the flame close to that open space.

Allow the flames to from the match to be drawn towrds the flow of air without being so close the air snuffs the match. The match flames should tilt inwards towards the cap.

This simple test shows the air flow direction. The flames can be allowed to burn down the match stick without going out until the flame gets close to your fingers.

Usually the flame can be blown out by the person doing this test before the flames consume half the stick. Carefully blowing out the match stick flame, without moving the match, one must note the direction of the smoke too.

The blown out match flames smoke must also be drawn into the space between the water heaters flue and into the open space beneath the down drafter diverter.

If any of the above does not happen exactly as noted above, redo the test to be sure it is being done correctly. Practice makes perfect.

If the reverse happens in the test, the flames snuff out, the match may be too close and or too far. If the match is held in the close to area but not inside the area space and the flames snuff out or point away from the space, the venting system is defective.

The defect may be caused by several conditions. Most commonly is an incorrectly installed vent cap on the outside vent pipe. As noted in detail above. The other may be a clogged, bent, damaged and or somehow restricted venting pipe.

In rare but possible instances, an interior inside the room and or closet space the appliance is in can cause a reverse venting effect. Another much too long and detailed reply to post. Professional help is highly suggested.

If you need further assistance, use the REPLY button to add any additional information or questions, etc. Using this method also moves the topic back up to the top of the list automatically.

Regards & Good Luck.
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Neither appliances ducting systems should be interconnected ever. Each appliance, water heater and dryer in this case, must have independent and seperate operating venting systems.

Once again, the reasons for and the detailed explainations of why are much to complicated to explain in full details in one reply.

Dryers have a fan to draw in warm air from the burner compartment and force it through the drum and out the ducting system. The entire venting system can be removed from the dryer and cleaned out and or replaced. Which ever is required.

The venting system has a vent hood installed on the exterior. Within it is a flapper valve. That flapper valve/door must be able to freely move outwards/open. If it is not able to do so the condition must be corrected.

Read the existing questions on the subject of dryers. Doing so will quickly provide you with answers to questions & provide additional information on how to resolve problems.
Old 08-31-03, 01:27 PM
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Smile Thank you!

Thank you very much for the fast and insightful reply.

Your detailed explanation is very much appreciated!

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