Flue gas booster fan

Unknown

on why it is used.

The Field Type “C” Chimney Top Draft Inducer provides negative pressure to overcome the effects of wind, cold chimneys, insufficient chimney height, and downdraft.

The Type C Draft Inducer is available in four sizes: 6", 8", 10" and 13" and is designed to provide years of trouble-free operation. It is insulated to withstand peak temperatures up to 1300° F and operates continually at 900° F without overheating the motor windings or bearings. It can operate with a standard manual on-off switch, or can be installed with the Field Controls variable speed motor control.

When to use a Chimney Top Draft Inducer

· To Provide Additional Air

A considerable amount of air is necessary to allow for good chimney draft. In many tightly constructed homes, this air is not readily available. The addition of a Type C Draft Inducer will compensate for lack of air by supplementing the chimney's natural draft.

· To Create Draft in Cold Chimneys

A chimney, especially on an outside wall, may be so cold prior to starting a fire that no draft exists. A Type C Draft Inducer switched on before starting the fire will provide draft until the chimney has become hot enough to generate a natural draft.

· To Prevent Occasional or Continuous Spillage

Spillage may be the result of several factors including downdraft caused by adjacent buildings, terrain or trees. Remodeling, new additions, or the addition of an exhaust fan can change airflows and result in poor draft. Or a chimney design inadequacy, such as an undersized flue, may prevent adequate draft.

PBCullen

Flue gas booster fan

I would like some information on booster fans used on top of chimneys. How can they work on gas fired furnaces without affecting efficiency?

Unknown

They are usually

used when a poor draft condition existed. They actually create a draft which improves the efficiency of the system. The entire chimney is in fact at a negative pressure which insures a proper draft.

Natural draft is usually created by delta "T" temperature difference and height. If that is not possible a draft induscer at the top of the vent is one way of insuring proper draft.

All equipment connected into that vent must then be interlocked to insure that they can not fire without the inducer running. Some inducers are set up to run continiously.

mikea23

I just ran into the same thing last week on two water heaters one 500,000 btu the other 200,000 btu. The call was no hot water in unit 1 I replaced the ignitor and pilot tube unit started. I was leting the unit come to temp and felt the draft rolling out. I found that the fans where controlled by a seperate switch that was turned off in Mech room. T urned it back on and unit performed fine. I then by passed the switch so they run 24/7. I also installed two splill switches on each unit for safty.

brad_25

flue boosters

where I live in Illinois some local codes require only an inline flue booster when horizontaly terminating pipes outdoors, my question is after being in this buisness for 11 years i have never come across a fan booster like the one pictured only on a poorly drafting chimney for a fireplace.Why not just fix the real venting problem instead of putting a bandaid on it?

Unknown

Mike that equipment

should not have been able to fire without the booster running. It needs to have an interlock switch installed as it is unsafe as it is now installed. Even though you have made it so the booster runs all the time if it stops due to motor failure the system will still come on and that is very dangerous.

Derheatmeister

Not only is it a dangerous situation it also wasting ALOT of energy having a Daft inducing fan pulling cold air across the heat exchanger and extracting heat from it and blowing it out the chimney.

PBCullen

Booster Fan

This brings me back to my original question about efficiency, how can you size the fan properly especially when there is more than one appliance on the same flue?

I would think make-up air would be very important to help prevent a negative pressure in the buildings envelop allowing unwanted gases to be drawn in.

Unknown

First of all

it has to be installed correctly. That being said the booster should not be running until a call for heat or in the case of a water heater being connected a call for hot water.

Then on any call the booster fan has to be interlocked with both appliances, this will insure that the units will not fire if the booster is not working.

As for sizing it does not change the requirement for the chimney or vent to have been sized correctly for the load. Then the booster is sized to the chimney.

I will not argue with the fact that perhaps a Draft Inducer would have been a better way to go in some cases.

In any case the case involved here is not installed correctly.

There are however many cases on commercial applications that whole chimney venters are used.

PB Cullen "make up air" is required to equalize air volume in buildings that have mechanical exhausting removing air from the building such as attic fans, bathroom fans, dryers and Jenn-Aire units to name a few.

Any gas or oil equipment would then need additional "air for combustion" (air in addition to make up air)which in this case would be needed as these devices only overcomes drafting problems and does not affect pressure in the building. They usually only run at about 1050 to 1550 RPMs.

PBCullen

Booster Fan

Thanks Tim,
You have been very helpfull.

mikea23

Thats why i installed not one but two spill switches at the flue base.

I agree the equipment should have been installed with the fans turning on first then the heaters. The spill switches will turn both units off if flue gas rollout happens.

If I was the origanal contractor I would install nothing but sealed combustion. The application is a large nightclub/resterant and with exhaust fans in not only the club but the kitchen if something happens to the make up air system it will be a neg pressure and will result in draft problems. That is the other reason I installed spill switchs.

In a perfect world I would have replaced both units and that was given as a option but the cost of a 500,000 btu heater and a 200,000 btu heater was lets say over 20K sealed combustion waterheaters for commercial aplications are very expensive. With a building that has ventallation and kept at a small neg pressure natural draft units should never be used.

Jim Davis_3

Never a bandade but a last resort

Booster fans are necessary on some installations where it is impossible to overcome the negative pressure in the building. Sometimes they are used when you have long horizontal runs and need to pull the flue gasses to the vertical chimney. They also are used on short chimneys. When sized properly they do give us the ability to vent into an undersized chimney.

The only time I have ever used the chimney cap inducer was on fireplaces. Inducers will create positive pressure in in cold chimneys and if they are not air tight, smoke and soot could leak out into the building on wood burning appliances.

Inducers if set up properly should help us make equipment more efficient because we now have regulated draft versus unregulated. They are totally unsafe when installed above a drafthood because they can create an "air curtain" affect and prevent venting altogether.

It takes special skills and training to install them and set them up correctly. However the manufacturers that make them don't always provide all the necessary information.

Unknown

Mike you are now

responsible for the job and spill switches are not enough they need to be interlocked.

RJ_4

flue

Get a hold of these guys. www.selkirk.com 800-992-vent (8368).