Poor draft or negative pressure issues?

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EbS-P

Minister of Fire
Jan 19, 2019
1,732
SE North Carolina
OP stated 15+ feet rear vent, A house with negative pressure using a portable AC drawing (air down the oil burner flue) With this info I’m guessing it less than optimal draft with negative pressure due to a tight building envelope or stack effect. Seems like approaching these one at a time. Adding flue height, air sealing the top story to reduce stack effect adding temporary fresh air intake ect. Not sure what the most efficient path is. I’m guessing adding a temporary length to the flue is where I would start. Air sealing can be a weekend project (windows and ceiling penetrations, exterior wall outlets and switches )

Taking a look up the clean out with your phone you can probably figure out if the liner is capped and where.

Hot fires with lots of kindling to start with short sleepers front to back so there is an air path all the way to the back Might help. Epa stove need to run hotter that’s how they get the clean burns to meet emissions.

Just my thoughts
 

neverstop

Member
Oct 11, 2020
108
new hampshire
OP stated 15+ feet rear vent, A house with negative pressure using a portable AC drawing (air down the oil burner flue) With this info I’m guessing it less than optimal draft with negative pressure due to a tight building envelope or stack effect. Seems like approaching these one at a time. Adding flue height, air sealing the top story to reduce stack effect adding temporary fresh air intake ect. Not sure what the most efficient path is. I’m guessing adding a temporary length to the flue is where I would start. Air sealing can be a weekend project (windows and ceiling penetrations, exterior wall outlets and switches )

Taking a look up the clean out with your phone you can probably figure out if the liner is capped and where.

Hot fires with lots of kindling to start with short sleepers front to back so there is an air path all the way to the back Might help. Epa stove need to run hotter that’s how they get the clean burns to meet emissions.

Just my thoughts
I'll check with my phone when I get home, that'll be easier than moving the stove.

The last fire I attempted used more kindling/newspaper and seemed to take off better. With the door closed, all of the kindling burned down and the E/W loaded logs starting to catch the fire died.

By sleepers do you just mean put in short small splits N/S to elevate the larger splits off the bottom of the firebox? This is just to start the fire to establish a nice bed of coals correct?
 

EbS-P

Minister of Fire
Jan 19, 2019
1,732
SE North Carolina
I'll check with my phone when I get home, that'll be easier than moving the stove.

The last fire I attempted used more kindling/newspaper and seemed to take off better. With the door closed, all of the kindling burned down and the E/W loaded logs starting to catch the fire died.

By sleepers do you just mean put in short small splits N/S to elevate the larger splits off the bottom of the firebox? This is just to start the fire to establish a nice bed of coals correct?
If draft is weak and I want to get my reload going fast I will put the short NS sleepers in on a cooler bed of coals too. If the kindling burned well and the bigger spots didn’t use more kindling to get it going. I only use 2 medium splits on a cold start. But my firebox is smallish shallow and sloped back to front. 1.7 cu ft.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
They would have needed to extend the liner after the tee down to the cleanout and then capped the liner at the cleanout so that it could be removed when cleaning. It probably is capped, but if it is not capped, that's a problem. It could ruin draft.

OP stated 15+ feet rear vent, A house with negative pressure using a portable AC drawing (air down the oil burner flue) With this info I’m guessing it less than optimal draft with negative pressure due to a tight building envelope or stack effect. Seems like approaching these one at a time. Adding flue height, air sealing the top story to reduce stack effect adding temporary fresh air intake ect. Not sure what the most efficient path is. I’m guessing adding a temporary length to the flue is where I would start. Air sealing can be a weekend project (windows and ceiling penetrations, exterior wall outlets and switches )

Taking a look up the clean out with your phone you can probably figure out if the liner is capped and where.

Hot fires with lots of kindling to start with short sleepers front to back so there is an air path all the way to the back Might help. Epa stove need to run hotter that’s how they get the clean burns to meet emissions.

Just my thoughts
There is a cap on it apparently.
20211119_182221.jpg
 
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begreen

Mooderator
Staff member
Nov 18, 2005
91,384
South Puget Sound, WA
Good deal, cross that one off the list. Does the fire behavior improve notably if a nearby door or window is open 1"?
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Good deal, cross that one off the list. Does the fire behavior improve notably if a nearby door or window is open 1"?
I was able to try another burn. I didn't notice a visual change when a window was open/not. Although I was only burning 2 medium sized splits and stove top maxed out at 450. Outside temp at start was 37 degrees. Clear skies.

I used sleepers on the bottom, then medium splits, then kindling, then paper, and wood scraps on top. Used a heat gun then newspaper above the baffle to warm the flue. Lit the paper and left the door cracked until kindling caught well then latched it.

It took off well, and the fire didn't die after the kindling fell. This was 11 minutes in:

30 minutes in it was about 375 stove top and looked like this: (also no visible smoke from chimney)

20211120_092558.jpg 20211120_093606.jpg 20211120_095021.jpg 20211120_095245.jpg
Primary air was 100% open the whole time, bypass open. After 3 hrs had coals and 300 degree stove top temp.

Now this was by far the best burn I've had so far, I attribute that to the sleepers. I have to check wood on a fresh split but outside is 11%. Smoke still came out of the door after kindling caught. Once the fire was more established I couldn't tell if smoke was coming out but standing above the door it smelt like fire. Once it was coals I pulled them forward and some ash flew out. Still had the same smell but no smoke.

With this result I wouldn't be so paranoid about it, but I have a newborn so I'd like to mitigate all smoke exiting into the room. The other concern i have is that if the fire doesn't take off I can't open the door to remedy it without smoke billowing out. The vigilant I could start it with the doors open and screw around with it as much as I neded to without any concerns. Is that just a difference with the epa stoves?
 

EbS-P

Minister of Fire
Jan 19, 2019
1,732
SE North Carolina
I was able to try another burn. I didn't notice a visual change when a window was open/not. Although I was only burning 2 medium sized splits and stove top maxed out at 450. Outside temp at start was 37 degrees. Clear skies.

I used sleepers on the bottom, then medium splits, then kindling, then paper, and wood scraps on top. Used a heat gun then newspaper above the baffle to warm the flue. Lit the paper and left the door cracked until kindling caught well then latched it.
View attachment 285876
It took off well, and the fire didn't die after the kindling fell. This was 11 minutes in:
View attachment 285877
30 minutes in it was about 375 stove top and looked like this: (also no visible smoke from chimney)
View attachment 285878
View attachment 285879
Primary air was 100% open the whole time, bypass open. After 3 hrs had coals and 300 degree stove top temp.

Now this was by far the best burn I've had so far, I attribute that to the sleepers. I have to check wood on a fresh split but outside is 11%. Smoke still came out of the door after kindling caught. Once the fire was more established I couldn't tell if smoke was coming out but standing above the door it smelt like fire. Once it was coals I pulled them forward and some ash flew out. Still had the same smell but no smoke.

With this result I wouldn't be so paranoid about it, but I have a newborn so I'd like to mitigate all smoke exiting into the room. The other concern i have is that if the fire doesn't take off I can't open the door to remedy it without smoke billowing out. The vigilant I could start it with the doors open and screw around with it as much as I neded to without any concerns. Is that just a difference with the epa stoves?
Don’t think it’s realistic to eliminate ALL the smoke smoke. If you smell it you’re getting smoke in the house. I’m running two HEPA filters and adding a MERV 13 box fan filer.

So it sounds like you are making progress. I would leave the window cracked for a an hour. You probably won’t SEE any difference in flame but burn rate might improve. So I think the next step is to see how it drafts on a hot reload. I add two pieces of kindling first in the bottom of my re load and two more on the top. I want to re establish a good draft ASAP and get the secondaries burning fast as well

Wish a good hot coal bed I see different burn characteristics than I do with a cold start but but if I’m not careful to get a good air flow channel the relaod can struggle.

It’s in my clipboard so I’m just gonna post this saying it’s the best money I’ve spent on my stove.
With kids life gets hectic and I like knowing there is a temp alarm I get called away from the stove.


Edit check that split face MC %. It may surprise you.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Don’t think it’s realistic to eliminate ALL the smoke smoke. If you smell it you’re getting smoke in the house. I’m running two HEPA filters and adding a MERV 13 box fan filer.

So it sounds like you are making progress. I would leave the window cracked for a an hour. You probably won’t SEE any difference in flame but burn rate might improve. So I think the next step is to see how it drafts on a hot reload. I add two pieces of kindling first in the bottom of my re load and two more on the top. I want to re establish a good draft ASAP and get the secondaries burning fast as well

Wish a good hot coal bed I see different burn characteristics than I do with a cold start but but if I’m not careful to get a good air flow channel the relaod can struggle.

It’s in my clipboard so I’m just gonna post this saying it’s the best money I’ve spent on my stove.
With kids life gets hectic and I like knowing there is a temp alarm I get called away from the stove.


Edit check that split face MC %. It may surprise you.
Just split a relatively large split. Inside surface measured 15%. The end was 12%. I threw 1 small split i had in on the coals and it caught within a couple of minutes with the door closed. Its 45 degrees now, so the window has been open for awhile to keep the house temp down in low 70s. I'll check out that thermometer thanks.
 
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EbS-P

Minister of Fire
Jan 19, 2019
1,732
SE North Carolina
Just split a relatively large split. Inside surface measured 15%. The end was 12%. I threw 1 small split i had in on the coals and it caught within a couple of minutes with the door closed. Its 45 degrees now, so the window has been open for awhile to keep the house temp down in low 70s. I'll check out that thermometer thanks.
Another item checked off. I just got the wireless version for my basement stove. Super handy. Regular for upstairs.
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,384
South Puget Sound, WA
As the weather cools down you will want to be loading the stove with 4-5 splits for a longer burn.
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,384
South Puget Sound, WA
Yes, next fire try at least 3 splits and for sure close the bypass to engage the cat. A cat thermometer would help with determining when, but based on the pictures above I would guess it would be ok at around the 15 minute point with a similar burn.

It's not conclusive, but there is growing evidence that this stove and its sibling the GM60 need a strong draft. A test would be to temporarily remove the chimney cap and stick a 3 ft length of cheap 6" warm air duct, crimp-down, into the top of the liner. If that makes a big difference in the way the stove burns then extending the chimney should be considered.
 
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neverstop

Member
Oct 11, 2020
108
new hampshire
Yes, next fire try at least 3 splits and for sure close the bypass to engage the cat. A cat thermometer would help with determining when, but based on the pictures above I would guess it would be ok at around the 15 minute point with a similar burn.

It's not conclusive, but there is growing evidence that this stove and its sibling the GM60 need a strong draft. A test would be to temporarily remove the chimney cap and stick a 3 ft length of cheap 6" warm air duct, crimp-down, into the top of the liner. If that makes a big difference in the way the stove burns then extending the chimney should be considered.
The stove has a cat thermometer that has an active zone on it. I'll try that next burn.

Don't know when I'd have time to check the extended chimney. If it wouldn't be too much $$ I might just go ahead and extend it to play it safe.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Too warm for a burn today, but would the stove not being level have any effect on smoke rollout or performance? I used a level and the back of the stove was definitely higher than the front. It is now level after adjustment.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Yes, next fire try at least 3 splits and for sure close the bypass to engage the cat. A cat thermometer would help with determining when, but based on the pictures above I would guess it would be ok at around the 15 minute point with a similar burn.

It's not conclusive, but there is growing evidence that this stove and its sibling the GM60 need a strong draft. A test would be to temporarily remove the chimney cap and stick a 3 ft length of cheap 6" warm air duct, crimp-down, into the top of the liner. If that makes a big difference in the way the stove burns then extending the chimney should be considered.

I was able to burn again tonight with temps in the high 30's. I took an actual measurement of the chimney today, it is 17 ft from stove flue exit to the top of the liner.

I got lazy with the top down load and probably didn't add enough kindling and fought starting the fire for 45 minutes. Wasn't able to open the door past 2" crack without smoke rollout during this so it made it hard. Had sleepers N/S, 2 larger splits E/W, 1 small split on top, then paper/kindling on top and paper stuffed throughout where there were gaps.

Once the fire actually caught I waited until the cat thermometer (doesn't have #'s just sections, inactive, active, overfire) reached the middle of the active range then closed the by-pass. I left the primary 100% open for 20 minutes per the manual. Then I closed it down to what should have been a "medium-low burn" per the manual (primary 1/4" pulled out from lowest setting). Stove top settled to around 500F for 45min-1hr. Fuel was probably the limiting factor here as by the time I closed it down the larger splits were almost in the coal stage. I don't know how long it burnt as I went to bed 2.5hrs after I was finally able to start the fire.

Here are some videos of the stove burning. Should there be more secondary combustion occurring?

By-pass open primary 100% - stove top was around 400F at this point



By-pass closed primary 100% - stove top was around 525F at this point



Below are sequential images after I just the primary down to "medium-low burn" (time from 1st image to last is maybe 30-45 minutes):

20211122_223705.jpg 20211122_214648.jpg 20211122_212458.jpg 20211122_213906.jpg

I observed some large flames and burning appear every once in awhile when it was transitioning to the coal stage and there were no constant visible flames. Is this normal?

Is there anything of concern from the pictures/videos, or does everything seem to be burning and working correctly?
 

EbS-P

Minister of Fire
Jan 19, 2019
1,732
SE North Carolina
What I’m seeing looks pretty good. A larger fuel load will mean you can cut the primary air more and really get the secondaries going. This is about 4-6 cold starts worth of kindling for me. I stuff it clear full to the baffle with kindling. Get everything good and hot and good coal bed. Once it’s all hot and going bypass closed you can start cutting the air back and playing with burn rate and temps. I’m terrible at loading consistently ie same amount, size, species. Now I know my stove better it’s not an issues but when first learning it makes a things easier to learn.

More kindling is always better in my opinion. If the splits don’t take off you needed more.

8134B27E-8675-4360-AEC6-E6FFD1086BBA.jpeg
 
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neverstop

Member
Oct 11, 2020
108
new hampshire
What I’m seeing looks pretty good. A larger fuel load will mean you can cut the primary air more and really get the secondaries going. This is about 4-6 cold starts worth of kindling for me. I stuff it clear full to the baffle with kindling. Get everything good and hot and good coal bed. Once it’s all hot and going bypass closed you can start cutting the air back and playing with burn rate and temps. I’m terrible at loading consistently ie same amount, size, species. Now I know my stove better it’s not an issues but when first learning it makes a things easier to learn.

More kindling is always better in my opinion. If the splits don’t take off you needed more.

View attachment 286135
Oh the secondaries kick in when the primary is closed down? That makes sense; I guess I never really thought about that. So basically the primary is restricted so the draft pulls in air via the secondaries?

I didn't want to load too much wood into the stove as it was about 8pm when I started the fire. I was concerned about burning overnight since I don't have a lot of experience under my belt with the stove. I had more kindling I just got lazy I guess. I need to change my mentality that the purpose of the startup is to establish a coal bed first and foremost. Wasting kindling is way better than babysitting the fire for 30+ minutes to get it to light.
 

bigealta

Feeling the Heat
May 22, 2010
349
Utah, NJ
I posted this Top down set up on a few other threads. But posting it here to show how high the firebox can be filled. To get it to start faster use smaller splits on the 2nd row of splits and perhaps more kindling in the middle as well. The goal is to light it close the door and not reopen the door till reload time.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
I posted this Top down set up on a few other threads. But posting it here to show how high the firebox can be filled. To get it to start faster use smaller splits on the 2nd row of splits and perhaps more kindling in the middle as well. The goal is to light it close the door and not reopen the door till reload time.
thank you for the link, any reason you don't use newspaper or another starter?
 

neverstop

Member
Oct 11, 2020
108
new hampshire
I finally heard back from hearthstone about smoke spillage and any relevant baffle redesign between it and the GM60. They said the baffle change was unrelated to smoke spillage and to allow for the rear exit of the Shelburne. The GM60 and Shelburne share baffles.

The did say the following though:
For rear exit connection, the recommended minimum chimney height is 19 feet (5.8m) off the floor or 16 feet 6 1/8 inches (5.2m) from the top of the stove. The recommended maximum chimney height is 30 feet (9m).
Based on my re-measurements I'm currently at: 16' 8" from the top of the flue and 18' 2" from the floor. 1.5' of that is from the terracotta tile and the cap. So it seems even though my burning results look to be "good" I should add chimney height because I'm below minimum.

I have questions about the easiest way to go about this. I'm thinking removing the terracotta tiles above the chimney, adding this transition plate flex to class a, and then adding on however much class A pipe I need to remedy the smoke rollout issue on cold starts. Would that be a good solution? I'd also insulate the liner.
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,384
South Puget Sound, WA
I finally heard back from hearthstone about smoke spillage and any relevant baffle redesign between it and the GM60. They said the baffle change was unrelated to smoke spillage and to allow for the rear exit of the Shelburne. The GM60 and Shelburne share baffles.

The did say the following though:

Based on my re-measurements I'm currently at: 16' 8" from the top of the flue and 18' 2" from the floor. 1.5' of that is from the terracotta tile and the cap. So it seems even though my burning results look to be "good" I should add chimney height because I'm below minimum.

I have questions about the easiest way to go about this. I'm thinking removing the terracotta tiles above the chimney, adding this transition plate flex to class a, and then adding on however much class A pipe I need to remedy the smoke rollout issue on cold starts. Would that be a good solution? I'd also insulate the liner.
Yes, that's the proper way to do it. The chimney height guidance is helpful, but there are factors that can affect this. Things like locatoin of the stove in the house, location of the house relative to the terrain, and altitude can also affect draft. The manual's listed draft requirement of .08 to .15 wc is quite high compared to other stoves, so adding 3 ft to the chimney is not unreasonable.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Yes, that's the proper way to do it. The chimney height guidance is helpful, but there are factors that can affect this. Things like locatoin of the stove in the house, location of the house relative to the terrain, and altitude can also affect draft. The manual's listed draft requirement of .08 to .15 wc is quite high compared to other stoves, so adding 3 ft to the chimney is not unreasonable.
Anything under 5' doesn't need to be additional bracing right?
 

begreen

Mooderator
Staff member
Nov 18, 2005
91,384
South Puget Sound, WA
Right.
 

bigealta

Feeling the Heat
May 22, 2010
349
Utah, NJ
thank you for the link, any reason you don't use newspaper or another starter?
Didn’t use any paper or firestarters just to show neither are needed. You can use whatever you want. I like skipping those aids, guess I’m a bit of a pyro. I’ll be putting together a few more variations on different style top down set ups this winter..
The key is light it, close the door and don’t reopen door till reload.
 

neverstop

Member
Oct 11, 2020
108
new hampshire
Didn’t use any paper or firestarters just to show neither are needed. You can use whatever you want. I like skipping those aids, guess I’m a bit of a pyro. I’ll be putting together a few more variations on different style top down set ups this winter..
The key is light it, close the door and don’t reopen door till reload.
Oh ok. And yes that is the ideal outcome to not open until reload is needed.

I tested opening the door when the fire was raging and I still got flames escaping the firebox. Fire burns well once established.