Barometric Damper General Questions

[longboarder2]

i posted the other day about installing a baro damper to my harman sf-160 (not a gasser). i have some actual readings now and have some questions.

the issue: i feel as though i am burning too much wood too fast and not heating the water to it's potential.

equipment: harman sf-160 add-on boiler, 48" tall 6" smokepipe riser to 30' 7" all-fuel flue to open topper.

what i've done to extend burn times: added steel plates on top of firebox grates to reduce air intake and maintain embers/coals. have lower air intake door just under halfway open.

what i know about baro dampers: they exist. they are meant to equalize/reduce draft between the flue and the unit.--have no idea how to fine tune it or what the desired effects would be for my application (numbers wise)

draft readings: over the fire: .07 (probe put in draf knob opening on loading door) @ the flue collar on back of unit: .08

my questions: 1.) is the baro damper the answer to my problem? (burning too much too fast)

2.) what kind of draft numbers should i be seeing?

3.) how far above the collar on the riser should it be installed?

4.) when starting the fire and getting the unit going (sometimes twice a day) do i need to prop the damper shut until establishing draft to keep smoke from pouring into the house?

5.) as the fire dies out and draft diminishes, will smoke leak out of the damper door into the house?

6.) by slowing the draft am i creating more of a potential for creosote buildup?

the wood boiler has been effective in heating the house and reducing my oil bills---just need some fine-tuning on my wood intake.

any info would be greatly appreciated as harman continues to be a mediocre source of tech advice at best and there's not a lot of guys around here operating these things to gather info from.

thanks!

 

[BoilerBob]

(broken link removed to http://hearthnhome.com/downloads/installManuals/SF160_SF260_SF360.pdf)
LB - I don't know if you have the manuel,

It talks about draft and damper.

 

[longboarder2]

yeah, i have it. they recommend a min. draft of .06. so, will adding the damper and tuning my draft down to .06 make a significant difference in how much wood i burn?

 

[91LMS]

my boiler manual mentions the same thing about a barometric damper. my worry is that a damper would mix room temp air cooling the chimney and cause creosote build up.

 

[BoilerBob]

I have the same issues. I have no creosote problems now, but I know too much heat is going up the chimmney.

Trying to convince myself to try it, only $30 if I have to remove it.

 

[maple1]

From my experience (none of which is with a Harman):

1) - Maybe

2) - You should see what your unit specs. (0.6 in this case).

3) - Doesn't really matter.

4 & 5) - No.

6) - Maybe. There will likely be buildup around the damper, but it is relatively easy to scrape out through the damper opening. Most of my buildup when I was running a smoker & a baro was at the top of the chimney. You can minimize or eliminate buildup around the baro by placing it out of the smoke stream (e.g. on the bottom of a T at the bottom of your chimney, or on the end of a T at your boiler outlet)

Was the .08 reading in the middle of a typical burn? Is your chimney exposed to wind? I think if you watched the readings over a period of time while there was any wind at all happening, you might see some very higher readings. And on the tuning, you simply adjust/set the draft by screwing in or out a weighted disk on the back of the damper flap.

 

[Clarkbug]

If you are seeing .07 and .08, and the minimum is .06, I would be hesitant to think that is your problem at this point. Especially since its so cold out right now, which tends to improve your draft.

I would take some of the advice from maple and measure over the course of the next few weeks to see what you really have for a draft during various stages of a burn, and during several different types of weather.

Can you provide any other info as far as to why you think that you arent getting the heat out of your boiler? Is your wood good and seasoned? What sort of pumping do you have through the boiler?

 

[91LMS]

4 & 5) - No.

6) - Most of my buildup when I was running a smoker & a baro was at the top of the chimney.

that is what would make me skeptical. i cold start my boiler daily and keep an eye on the top of the chimney now where it doesnt stay hot enough all the time. the baro damper will cool it down quite a bit right?

 

[longboarder2]

where is the more important draft reading; at the firebox or the flue collar?

 

[maple1]

that is what would make me skeptical. i cold start my boiler daily and keep an eye on the top of the chimney now where it doesnt stay hot enough all the time. the baro damper will cool it down quite a bit right?

The baro would cool the chimney down so when it is open, yes - whether or not that is enough to make significantly more creosote in your chimney would likely depend on the individual situation. Which is why I said 'maybe'. If I was putting a baro in I would do so knowing that it might, and adjust my chimney maintenance procedures & timings accordingly.

Do you get creosote buildup in your chimney now? How often do you need to sweep? I swept in early October before firing up, then usually late December or early January, then again towards the end of heating season mid-March or so. I'm glad that routine is now history for me. I think most of my creosote builup was from an inefficient boiler - if I ran it 'wide open', there wasn't much creosote but I wasn't getting much heat out of my wood either. If I damped the draft down I would get more heat out of it, but started getting into Creosote City.

 

[maple1]

where is the more important draft reading; at the firebox or the flue collar?

I think it is most always in the flue when talking wood burners - I think 'over the fire' is most often an oil burner thing. They most likely wouldn't differ that much anyway unless there are excessive draft restrictions in the heat exchanging that would 'soak up' the draft between the flue & firebox. My boiler specs flue draft. Plus it must be kind of harder to get an over fire draft reading in a wood firebox when it's burning?

On the face of it, I'd agree with Clarkbug - 0.07 doesn't sound that out to lunch compared to a 0.06 spec. But that 0.06 might be a maximum spec, and the 0.07 you measured is likely the minimum seen. I actually would have expected more than 0.07 from a 30' chimney with a fire going - your chimney sounds almost identical to mine and I never see less than 0.1 with a fire going, with no effort put into sealing of pipe joints.

 

[BadgerBoilerMN]

This is what we follow for gas and oil. It explains the concept. Your particular boiler specs should come from the manufacturer as they should know the draft. Each installation is different so experimentation is necessary. Kudos for reading the draft.

(broken link removed to http://www.cbs.state.or.us/bcd/programs/boiler/boilerdampers.pdf)

 

[91LMS]

Do you get creosote buildup in your chimney now? How often do you need to sweep? I swept in early October before firing up, then usually late December or early January, then again towards the end of heating season mid-March or so. I'm glad that routine is now history for me. I think most of my creosote builup was from an inefficient boiler - if I ran it 'wide open', there wasn't much creosote but I wasn't getting much heat out of my wood either. If I damped the draft down I would get more heat out of it, but started getting into Creosote City.

i wouldnt say i get a lot of creosote. i swept after 6 weeks and a cord of wood on a virgin chimney. i noted a glazed look on my flue where the wind blows the smoke around. after i swept i didnt get enough creosote to even talk about in the cleanout. black flakey but had a glaze above the roof line. nothing built up just glossy.(this was a month ago) last night tore the pipe off the boiler to look and saw light brown fuzz inside the pipe and on the distance of flue i can see with a strong flash light and mirror (between 1/16th -1/8th"). i will sweep again this weekend to be sure. wish i could make the glaze at the top go away and fear of building more and possibly having problems..... stack temps 325-375 confirmed with ir gun on initial burns and fall off to 300 as the wood burns the gasses off.

 

[taxidermist]

what was the weather like when you took the readings? They say a min of .06 and your seeing .07 .08 then I would say your fine if the weather was not windy. Now if you take a reading when its really cold and windy and you readings are .10 to .12 then I would say your pulling the heat from your boiler up the chimney.

 

[longboarder2]

the last two days have been the coldest here to date in the teens with wind chills in the single digits. the wind conditions are blustery---worse yesterday than today, but definitely a steady 5-10 with 15-20 gusts. the readings were taken yesterday and today in those conditions.

 

[maple1]

My guage would likely be hitting in the area of 0.2 under those conditions.

OK, I just checked. It's -19c here right now with light wind gusts. Sounds like we have very similar conditions, and very similar chimneys. My fire right now is on the tail end of a burn. I held my baro closed and the guage went to 0.18". I would have expected your draft to be higher than 0.07-0.08 under those conditions - that's sort of backed up by my boiler manual & literature that specs 0.08" draft, and in another place calls for a 7m chimney. Anybody else have experience to share?

 

[taxidermist]

the last two days have been the coldest here to date in the teens with wind chills in the single digits. the wind conditions are blustery---worse yesterday than today, but definitely a steady 5-10 with 15-20 gusts. the readings were taken yesterday and today in those conditions.

Then I would say your fine.

 

[longboarder2]

next, i was going to wait for a little rise in the temps here and try to shut the air door at the bottom, except for the idle holes and try to control the fire with the draft knobs on the loading door---anyone doing that?

 

[AndrewPEI]

I have a Harman 260 boiler, first year with it, and have tried controlling the fire with the draft knobs, no noticeable difference in burn time, although I didn't run many tests like this, as I was afraid if the power was off while I was away or sleeping it could boil over. Was also unable to get the flue temp over 250 with using the front knobs, which would build the creosote up fast. The best I have found so far is to block off the front 1/3 or so of the grates blocked off with Firebrick, and cut my wood to about 18" -20" even though it can take 24", and keeping them as close to the door as possible. Doing this extended burn times a bit, the biggest plus was that it now keeps coals for many hours after the fire is out. I do not have a baro damper, but I think this is what I will try next. I have burned about 4 cord from the first week of October to now, Maple and birch with 25% softwood mixed in as well, no other heat source, heating 2000 Sq feet in Eastern Canada, so not too bad, on track to burn 6.5-7 before the first of May.

 

[AndrewPEI]

A neat modification that I want to try someday, probably a summertime modification is to take the draft knobs off and take the damper off of the ash pan drawer, pick up a second one and put them over the door knob drafts and use them to control the fire, shutting off the air from below. I think wood burns more efficiently when most/all of the air is supplied over/at the fire as opposed to under it. Under the fire air seems to push the heat up the flue faster, and burn the wood up quicker.

 

[BoilerMan]

A neat modification that I want to try someday, probably a summertime modification is to take the draft knobs off and take the damper off of the ash pan drawer, pick up a second one and put them over the door knob drafts and use them to control the fire, shutting off the air from below. I think wood burns more efficiently when most/all of the air is supplied over/at the fire as opposed to under it. Under the fire air seems to push the heat up the flue faster, and burn the wood up quicker.