Thread: booster fan

The wood stove today had an electric booster fan at the top of the flue. It seems like a pretty tough environment for an electric component, but it was working. There was no fire today. What problems can this cause, and why would this be installed? I'm assuming that there was a problem with the wood stove not drafting properly. Would you leave it on after the fire was good and hot? Never seen this one before.

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Chimney Top Draft Inducers | Field Controls

Jim, I would be concerned first of all about that chimney. Is it listed to UL 103HT or is it air cooled chimney for a factory built fireplace?

Anytime a chimney requires an exhaust fan for solid fuel, it must have an alarm with battery backup to alert upon the loss of power.

Any more pics/ info. on the rest of the chimney and stove installation?

It is a Dura Plus HT flue. It is enclosed outside, with adequate air spaces to combustible inside the enclosure. The only listing I saw on it is 247J, but that may be an internal Duravent model number. They don't appear to manufacture Dura Plus any longer.

I found a few similar draft inducers, but as usual you are exactly right on that model. That's the one.

There is no battery back up or alarm. Do you think they need it (the fan) after the fire is going? It's the only one I've ever seen in this area, and lots of people have a similar set up. The flue is a little high, but not that big of a deal. Certainly not unusual in the overall height of the flue. It's connected to a Lopi Endeavor wood stove.

Originally Posted by Jim Robinson

It is a Dura Plus HT flue. It is enclosed outside, with adequate air spaces to combustible inside the enclosure. The only listing I saw on it is 247J, but that may be an internal Duravent model number. They don't appear to manufacture Dura Plus any longer.

I found a few similar draft inducers, but as usual you are exactly right on that model. That's the one.

There is no battery back up or alarm. Do you think they need it (the fan) after the fire is going? It's the only one I've ever seen in this area, and lots of people have a similar set up. The flue is a little high, but not that big of a deal. Certainly not unusual in the overall height of the flue. It's connected to a Lopi Endeavor wood stove.

What? SDP DuraPlus in 6, 7 & 8" all fuel chimney (UL 103 HT) Trip wall isn't made anymore? I hadn't heard that...where did you get that from?

Max (supported) vert. hgt. 35', 2" clearance from combustibles. UL File No. MH7399. Here's a link to the file (clickable link): DDXU.MH7399 - Chimneys, Residential Type and Building-heating Appliance

The double asterik (**) on the table is indication of HT (UL 103HT) listing.

Here's a snippet from the file:

These chimneys shall be installed with all required Listed parts specified in the Installation and Maintenance Instructions provided with each chimney system.

Residential Type Chimneys shall be installed with the specified minimum clearance (air space) to combustible enclosing walls, and roof structure, and with clearances at floors, joists, and ceilings as established by the installation of designated factory furnished supports and firestop spacers.

Chimneys for use with offsets shall incorporate no more than the maximum number of elbows with the related maximum chimney height as specified in the installation instructions. The chimney heights indicated in the following table represent a specific support system that provides for the maximum chimney height. The maximum chimney height shall not exceed the specified height for the support system indicated in the instructions.

The battery back-up is not for the fan, its for the audible alarm which must sound signaling a power failure. If not running presence is obstructive to draft.

[quote=H.G. Watson, Sr.;216461]What? SDP DuraPlus in 6, 7 & 8" all fuel chimney (UL 103 HT) Trip wall isn't made anymore? I hadn't heard that...where did you get that from?

My bad, I do see it on their web site now. For some reason I was having a hard time finding it earlier.

The fan instructions don't mention the alarm. That's funny, because it sure seems like it would obstruct the flue if it weren't spinning electrically. Is that part of the mech codes for a draft assist fan?

They actually did a nice job of supporting and providing clearance for the flue. The stove is another matter, but when isn't it?

http://www.duravent.com/docs/product/L119_Oct10.pdf

This pipe if I remember is double walled air cooled with an internal blanket of ceramic fiber wrapped around the inner flue. Note the instructions call for a ventilated chase flashing. It also states not to modify their pipe or it voids the warranty and listing. By blocking the top of the chimney with a storm collar traps heated air inside the chimney pipe thus making it hotter. Even with an exhaust fan pulling flue gases, this chimney could over heat.

At the very least, the AHJ would have to approve this installation based upon some type of test reports showing how to adapt this exhaust fan without compromising the listing.

Originally Posted by Bob Harper

http://www.duravent.com/docs/product/L119_Oct10.pdf

This pipe if I remember is double walled air cooled with an internal blanket of ceramic fiber wrapped around the inner flue. Note the instructions call for a ventilated chase flashing. It also states not to modify their pipe or it voids the warranty and listing. By blocking the top of the chimney with a storm collar traps heated air inside the chimney pipe thus making it hotter. Even with an exhaust fan pulling flue gases, this chimney could over heat.

At the very least, the AHJ would have to approve this installation based upon some type of test reports showing how to adapt this exhaust fan without compromising the listing.

I'm sorry Bob, but I believe you're mistaken about DuraPlus being a doulbe-walled chimney. DuraPlus (R) is triple walled all-fuel chimney. Perhaps you are thinking of DuraPlus HTC (R) which is double-walled all-fuel chimney; or another stove chimney system, such as DuraTech?

DuraPlus(R):

Meets UL 103 HT,

.016” 430 stainless steel outer wall or .018” galvanized steel outer wall.
.018” aluminized steel intermediate liner.
.016” 430 stainless steel inner liner.
Insulated layers of ceramic blanket plus ventilated air space.


DuraPlus HTC (R) "C" as in Canada, meets the ULC S629 Standard (2100 @ 10 mins) in addition to UL 103 HT) and IT is a double-walled pipe:

Thermal Tech II insulation (silica-ceramic blanket) encased between
inner and outer walls of .020” 430 stainless steel.


You can review the information HERE:

Link for DuraPlus (R) Product page (clickable link): DuraVent : Old Browser Notification

DuraPlus (R) Install guide (more recent, 2011): http://www.duravent.com/docs/product...de2011_web.pdf

DuraPlus(R) sales brochure: http://www.duravent.com/docs/product..._broch11_w.pdf


Link for DuraPlus HTC (R) Product page: DuraVent : Old Browser Notification

DuraPlus HTC (R) Install guide (2012): http://www.duravent.com/docs/product..._Apr2012_W.pdf



That having been shared, I'm still somewhat confused about what you've said about the Chimney Top draft inducer not being appropriate. This is a Class A Chimney, is it not? Is it the transition to the triple wall chimney that is in question? The Wood Stove below, or the Chimney system itself? Does Field Controlls have a Listing of some kind for this device? Is there a specific transition piece supplied by them? Is it an item specified by the stove manufacturer? What or which Class A chimneys is the inducer approved or listed for? (and who has "approved" or "listed" it?)

From: http://www.fieldcontrols.com/pdfs/04052900.PDF

The Type "C" Chimney Top Draft Inducer is designed for installation on smoke pipes, Type "B" vents, Type "L" vents and factory built Class "A" chimneys. The Type "C" Draft Inducer is installed on the top of the vent system outside of the building.

BTW, that pine looks awfully close to that chimney termination, and over the roof itself; and a complete Level II inspection should always be advised when property is changing hands.

HG thx for the links. I didn't have time to pull them to refresh my memory and I couldn't tell from the pics. The third pipe is barely visible in the cooling slots at the pipe ends.

A triple walled chimney works on a thermosyphon. As the chimney is fired, the inner flue is warmed. The air in the concentric space is heated, becomes buoyant and establishes a draft. Since the bottom of the middle pipe does not close off at the base but communicates with the outer cooling space, it draws in cooling air. The hotter the flue, the more cooling air is drawn in. Bob Thulman patented this design back about 1949 and it was later adapted to factory built fireplaces around 1955. Heatilator used solid packed chimneys of the day until about 1985 when they switched to air cooled.

As long as this chimney is listed to 103HT, the chimney as designed would be compatible with a woodstove but not a wood insert into a factory built Fp.

The chimney was listed with their cap. You can usually spot triple walled chimneys by the three distinct separations at the termination, which is what fooled me on this one. The third air slot is more hidden. However, when you remove the listed cap and cram this fan down on it then cover those slots with a storm collar, you defeat the thermosyphon cooling system. Therefore, unless Field Controls has some data showing their fan tested on this particular chimney, there is a strong case to call for its removal. It also tells you they have some other serious issues if this is a tall chimney and they have draft issues. It may be the particular stove in question as modern stoves do require a good draft.

I agree Bob, can't being fitting products on chimneys unless it is tested and listed for it.

Anyone else have a problem with the wiring?

Originally Posted by Mike Kleisch

I agree Bob, can't being fitting products on chimneys unless it is tested and listed for it.

Anyone else have a problem with the wiring?

You mean such as the temperature rating of the insulation?

And possibly some other items?

Originally Posted by Bob Harper

HG thx for the links. I didn't have time to pull them to refresh my memory and I couldn't tell from the pics. The third pipe is barely visible in the cooling slots at the pipe ends.

A triple walled chimney works on a thermosyphon. As the chimney is fired, the inner flue is warmed. The air in the concentric space is heated, becomes buoyant and establishes a draft. Since the bottom of the middle pipe does not close off at the base but communicates with the outer cooling space, it draws in cooling air. The hotter the flue, the more cooling air is drawn in. Bob Thulman patented this design back about 1949 and it was later adapted to factory built fireplaces around 1955. Heatilator used solid packed chimneys of the day until about 1985 when they switched to air cooled.

As long as this chimney is listed to 103HT, the chimney as designed would be compatible with a woodstove but not a wood insert into a factory built Fp.

The chimney was listed with their cap. You can usually spot triple walled chimneys by the three distinct separations at the termination, which is what fooled me on this one. The third air slot is more hidden. However, when you remove the listed cap and cram this fan down on it then cover those slots with a storm collar, you defeat the thermosyphon cooling system. Therefore, unless Field Controls has some data showing their fan tested on this particular chimney, there is a strong case to call for its removal. It also tells you they have some other serious issues if this is a tall chimney and they have draft issues. It may be the particular stove in question as modern stoves do require a good draft.

Thank you for the follow-up Bob.

I guess I wasn't entirely clear. I'm having difficulty finding any sort of data, approvals, or listing for the FC chimney-top fan itself, for any application.

Is or was there ever a "listing" (or for that matter any 3rd party certification/testing) of the Field Controls "chimney top draft inducer" for ANY application (and did that ever include a manufactured chimney, liner, or vent system of any kind) or just a self-declared "design"/intent?

HG, I'm not aware of any application specific listing for exhaust fans. Any listing on this appliance is probably just an electrical listing.

As Dale Feb likes to point out, a toaster oven may be UL listed for toasting bread but not as a chimney cap.

As for the application of this product to another mfd. listed product, are there any test reports? If this fan was installed in a masonry chimney or singled walled unlisted metal vent or smokestack, there would be no listing conflict. But installing it in an air cooled chimney is because no matter what you do, you change the dynamic of the cooling system. Even installing it in solid packed chimney changes thing. At higher speeds, this fan may actually result in cooler surface temps. around this chimney but that's my conjecture--not a tested result.

People use such fans all the time on solid packed chimneys serving wood fired pizza ovens with no problems. My main point is that when you adapt some other termination on air cooled chimneys, even a fan, you run the risk of causing a fire, voiding the warranty and listing of that chimney and any attached appliance.