Secondary Air Flow Restrictor

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Woodcutter Tom

Burning Hunk
Apr 28, 2019
169
Northern Illinois
Throughout last year I could not get the stove top temperatures (and thus heat in my house) that I expected from my Drolet Escape 1500. I was getting very high temperature reading in my stove pipe. ( Over 1000 degrees) Late in the season last it was determined that I had excessive overdraft which caused these readings. I installed a damper assembly in my double wall stove pipe. This helped reduce my draft, but not enough. My manometer readings were still above the .03 - .05 that the manufacture recommended. I experimented with two key dampers in single wall stove pipe, and that helped even more. Since the season was ending and the weather was getting warmer, I felt that I was going to need three dampers along my stove pipe to control the draft. My plan was to purchase a 24" length of double wall stove pipe and a 12 - 18 " length of telescoping double wall. This would allow me to place my damper between the telescoping section and the ceiling adapter. Then I could install 2 key dampers in the solid 24" section along with my manometer probe and my thermometer probe. Manometer at 3" above stove top; key dampers at 7" and 12" above stove top and temp probe at 20" above stove top.
The manufacture suggest various method of slowing down the draft; dampers; restrictors in the secondary burn tubes; and covering part of the secondary air inlet with heat proof tape.
I tried the burn tube restrictors but felt that they were useless for a couple of reasons. 1.) they are washer like devices that are installed into the ends of the burn tubes. They can be installed in either or all of the 4 burn tubes. They are too thin to fit in the tubes without possibly rotating when the tubes are handled. 2.) they do not offer any adjustment when a fire is burning. They can only be modified with a cold stove.
I thought about the tape method, but that seemed to have it's own set of adjusting issues. Pull the ash drawer; add or remove tape under a hot stove in an ackward position.
So all summer I thought about ditching my long double wall telescoping stove pipe for the 24" and the smaller telescoping section. Then a came up with another option. From some metal I had laying around the house, I made a sliding door type device which fits in front of the secondary air intake under the stove. I drilled two small holes in the bottom of the air intake and bolted my door holder to it. I attached a control rod to the sliding door which runs through a hole I drilled in the pedestal base. Now I can adjust the secondary air flow by closing the door. I can do this while a fire is burning without getting burned myself. I placed markings on the control rod so that I can visually see the position of the door from a distance.
I think this will work out better than having three dampers in my stove pipes. I still will have the one damper installed on top. I look forward to keeping the heat in the stove (and in my house) and not going up the chimney. Perhaps this might be helpful to others with excessive draft issues.

Secondary Air Open.jpg Secondary Air Closed.jpg
 
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EbS-P

Minister of Fire
Jan 19, 2019
1,465
SE North Carolina
I’m interested to see how it works out for you. I just installed an 1800 insert with 24’ of nearly straight insulated liner and on a 75 degree day with the basement at 75 to it was drafting. I started thinking how to control it. I had similar thoughts about secondary air control. But I got to thinking I’m sure there is a ratio primarily to secondary that keeps the stove clean burning. Dampers don’t change that ratio. One could probably look at the area of the primary and secondary intake and get a close approximation.

I would think at some point too little secondary air would significantly lower efficiency. But with careful control i think it would work. Once you find the right setting it shouldn’t need much fiddling with. Did you leave the damps or remove them.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,531
South Puget Sound, WA
With that setup I would note the secondary air setting that achieves good, controlled secondary burning on a very cold winter day and then put in a screw to stop it from being closed further or cut back the blade so that that secondary opening is maintained with the control pushed all the way in.
Also, have you experimented with closing off the boost air port(s?) on the stove?
 

Woodcutter Tom

Burning Hunk
Apr 28, 2019
169
Northern Illinois
I’m interested to see how it works out for you. I just installed an 1800 insert with 24’ of nearly straight insulated liner and on a 75 degree day with the basement at 75 to it was drafting. I started thinking how to control it. I had similar thoughts about secondary air control. But I got to thinking I’m sure there is a ratio primarily to secondary that keeps the stove clean burning. Dampers don’t change that ratio. One could probably look at the area of the primary and secondary intake and get a close approximation.

I would think at some point too little secondary air would significantly lower efficiency. But with careful control i think it would work. Once you find the right setting it shouldn’t need much fiddling with. Did you leave the damps or remove them.
I will leave in one damper assembly. I could not install the two key dampers without going to the 24" solid and 12 -18" telescoping stove pipe. My current telescoping section is at it's smallest limit when I install it. Key dampers can only be installed in a section with no overlap.
I'll report back later in the year with how this works out.
 
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Woodcutter Tom

Burning Hunk
Apr 28, 2019
169
Northern Illinois
With that setup I would note the secondary air setting that achieves good, controlled secondary burning on a very cold winter day and then put in a screw to stop it from being closed further or cut back the blade so that that secondary opening is maintained with the control pushed all the way in.
Also, have you experimented with closing off the boost air port(s?) on the stove?
I had thought of putting in a positive stop so that the door can't be closed completely or past a certain point. Experimenting will help me find this point.
For most of last year I did not even know I had boost air ports on this stove. Someone made a post about them for his Drolet stove and I was thinking "What the hell is he talking about?" After asking about the location, I found them on my stove. There are three. They were filled with ash and completely blocked. Once I learned about them I kept them clean and would often see flames shooting out 3 to 4 inches long. There is no mention in the user manual about them. Per your suggestion I asked SBI technical support about why they are not mentioned in the manual. His response was that the manuals are written by the stove engineers and he thinks they are trying to protect a trade secret. Well they were a secret, especially when the manual states to rake the ashes forward in the firebox......right into the ports and blocking them. Since the inlet for the ports is only an 1/8" diameter hole which the primary air plate covers unless 3/4 open, I don't see a method for blocking them unless I do so from the firebox side.
 
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EbS-P

Minister of Fire
Jan 19, 2019
1,465
SE North Carolina